Ann Taylor Sandbox 7 - Revision history

Peter A. Duden at 06:21, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:21:45 GMT

←Older revision		Revision as of 06:21, 8 October 2013
Line 6:		Line 6:
	Adenosine deaminase is involved in the degradation of purine nucleotides. It is especially active in lympocytes, and mutation of adenosine deaminase results in severe immunodeficiency. Adenosine deaminase contains an eight stranded parallel alpha/beta barrel with the active site in a deep pocket at the beta-barrel COOH-terminal end. <ref>PMID:1925539 </ref> The active site contains a <scene name='36/365340/Zinc_cofactor/1'>zinc cofactor</scene>, which coordinates to the 6-hydroxyl of the transition state analogue, 6-hydroxyl, 1,6-dihydropurine ribonucleoside. The <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> is coordinated to three histidine residues and an aspartic acid residue.		Adenosine deaminase is involved in the degradation of purine nucleotides. It is especially active in lympocytes, and mutation of adenosine deaminase results in severe immunodeficiency. Adenosine deaminase contains an eight stranded parallel alpha/beta barrel with the active site in a deep pocket at the beta-barrel COOH-terminal end. <ref>PMID:1925539 </ref> The active site contains a <scene name='36/365340/Zinc_cofactor/1'>zinc cofactor</scene>, which coordinates to the 6-hydroxyl of the transition state analogue, 6-hydroxyl, 1,6-dihydropurine ribonucleoside. The <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> is coordinated to three histidine residues and an aspartic acid residue.

-	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.	+	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the <scene name='36/365340/Purine_ring/1'>purine</scene> portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and <scene name='36/365340/Zinc_cofactor/1'>zinc</scene>, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated <scene name='36/365340/Glu217/1'>Glu217</scene> or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.		ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and <scene name='36/365340/Zinc_cofactor/1'>zinc</scene>, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated <scene name='36/365340/Glu217/1'>Glu217</scene> or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:17, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:17:02 GMT

←Older revision		Revision as of 06:17, 8 October 2013
Line 4:		Line 4:


-	Adenosine deaminase is involved in the degradation of purine nucleotides. It is especially active in lympocytes, and mutation of adenosine deaminase results in severe immunodeficiency. Adenosine deaminase contains an eight stranded parallel alpha/beta barrel with the active site in a deep pocket at the beta-barrel COOH-terminal end. <ref>PMID:1925539 </ref> The active site contains a <scene name='36/365340/Zinc_cofactor/1'>zinc cofactor</scene>, which coordinates to the 6-hydroxyl of the transition state analogue, 6-hydroxyl, 1,6-dihydropurine ribonucleoside. The zinc is coordinated to three histidine residues and an aspartic acid residue.	+	Adenosine deaminase is involved in the degradation of purine nucleotides. It is especially active in lympocytes, and mutation of adenosine deaminase results in severe immunodeficiency. Adenosine deaminase contains an eight stranded parallel alpha/beta barrel with the active site in a deep pocket at the beta-barrel COOH-terminal end. <ref>PMID:1925539 </ref> The active site contains a <scene name='36/365340/Zinc_cofactor/1'>zinc cofactor</scene>, which coordinates to the 6-hydroxyl of the transition state analogue, 6-hydroxyl, 1,6-dihydropurine ribonucleoside. The <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> is coordinated to three histidine residues and an aspartic acid residue.

	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

Peter A. Duden at 06:16, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:16:25 GMT

←Older revision		Revision as of 06:16, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and <scene name='36/365340/Zinc_cofactor/1'>zinc</scene>, , while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated <scene name='36/365340/Glu217/1'>Glu217</scene> or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and <scene name='36/365340/Zinc_cofactor/1'>zinc</scene>, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated <scene name='36/365340/Glu217/1'>Glu217</scene> or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:16, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:16:00 GMT

←Older revision		Revision as of 06:16, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated <scene name='36/365340/Glu217/1'>Glu217</scene> or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and <scene name='36/365340/Zinc_cofactor/1'>zinc</scene>, , while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated <scene name='36/365340/Glu217/1'>Glu217</scene> or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:14, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:14:45 GMT

←Older revision		Revision as of 06:14, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene>. orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated <scene name='36/365340/Glu217/1'>Glu217</scene> or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:12, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:12:21 GMT

←Older revision		Revision as of 06:12, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and His 238 orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene>. orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:11, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:11:54 GMT

←Older revision		Revision as of 06:11, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. Asp295 and His 238 orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and His 238 orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:11, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:11:21 GMT

←Older revision		Revision as of 06:11, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. ~~<scene name='36/365340/~~Asp295~~/1'>Asp295</scene>~~ and His 238 orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. Asp295 and His 238 orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:09, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:09:21 GMT

←Older revision		Revision as of 06:09, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and ~~<scene name='36/365340/His_238/1'>~~His 238~~</scene>~~ orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and His 238 orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.

Peter A. Duden at 06:09, 8 October 2013

Peter A. Duden — Tue, 08 Oct 2013 06:09:21 GMT

←Older revision		Revision as of 06:09, 8 October 2013
Line 8:		Line 8:
	The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.		The transition state analogue held in place mostly by polar interactions. The ribose group is close to the opening of the pocket, with the purine portion deeper in the pocket, close to the zinc. Nine hydrogen bonds stabilize the transition state-enzyme complex.

-	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>~~His238~~</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.	+	ADA is very stereoselective for the 6R isomer. This specificity is due to the location of the <scene name='36/365340/Zinc_cofactor/1'>catalytic zinc</scene>, <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His238</scene>. Interestingly, one face of the purine ring is exposed to polar groups and zinc, while the other face is only exposed to nonpolar residues. The proposed catalytic mechanism has <scene name='36/365340/Asp295/1'>Asp295</scene> act as a general base, while the <scene name='36/365340/Zinc_cofactor/1'>zinc</scene> acts as an electrophile to activate the water molecule. <scene name='36/365340/Asp295/1'>Asp295</scene> and <scene name='36/365340/His_238/1'>His 238</scene> orients the water and stabilizes the charge of the attacking hydroxide. The protonated Glu217 or the water hydrogen bonded to it could donate or share a proton with the N1 of the substrate.