Allophycocyanin
From Proteopedia
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Interestingly, the λmax of the chromophore can be tuned depending upon the protein binding it. For allophycocyanin, the λmax is 650 nm; in another phycobiliprotein, phycocyanin, the λmax is 625 nm, even though it uses the same chromophore. Phycocyanobilin is a highly flexible, linear tetrapyrrole that is covalently attached to the protein by a <scene name='Allophycocyanin/Cys/1'>thiol linkage</scene> to a cysteine in the protein. Allophycocyanin holds the <scene name='Allophycocyanin/Pigment/1'>pigment</scene> in place through a number of intermolecular interactions. <scene name='Allophycocyanin/Asn73/1'>Asn72</scene> forms hydrogen bonds with an amine in the pigment, while <scene name='Allophycocyanin/Arg86/1'>arginine 86</scene> interacts with a carboxylic acid that is exposed to the solvent. A key <scene name='Allophycocyanin/Asp87/2'>aspartic acid</scene> also holds the molecular planar. These interactions stabilize the pigment in the protein and hold the pigment planar. When the protein is unfolded, the pigment is no longer planar, and loses the ability to transfer red light to chlorophyll. | Interestingly, the λmax of the chromophore can be tuned depending upon the protein binding it. For allophycocyanin, the λmax is 650 nm; in another phycobiliprotein, phycocyanin, the λmax is 625 nm, even though it uses the same chromophore. Phycocyanobilin is a highly flexible, linear tetrapyrrole that is covalently attached to the protein by a <scene name='Allophycocyanin/Cys/1'>thiol linkage</scene> to a cysteine in the protein. Allophycocyanin holds the <scene name='Allophycocyanin/Pigment/1'>pigment</scene> in place through a number of intermolecular interactions. <scene name='Allophycocyanin/Asn73/1'>Asn72</scene> forms hydrogen bonds with an amine in the pigment, while <scene name='Allophycocyanin/Arg86/1'>arginine 86</scene> interacts with a carboxylic acid that is exposed to the solvent. A key <scene name='Allophycocyanin/Asp87/2'>aspartic acid</scene> also holds the molecular planar. These interactions stabilize the pigment in the protein and hold the pigment planar. When the protein is unfolded, the pigment is no longer planar, and loses the ability to transfer red light to chlorophyll. | ||
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| - | '''Fructose bisphosphate aldolase''' is an enzyme in glycolysis and gluconeogenesis. Glycolyis is responsible for the conversion of glucose into two three-carbon pyruvate molecules without the need for oxygen. The process generates two net ATP. The overall reaction is: | ||
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| - | Glucose + 2 NAD+ + 2 ADP + 2 Pi --> 2 pyruvate (3-carbon product) + 2 NADH + 2 ATP + 2 H20 + 4 H+ | ||
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| - | Gluconeogenesis is responsible for maintaining the appropriate levels of blood glucose in animals by generating glucose from non-carbohydrate precursors. Gluconeogenesis can make glucose from lactate, pyruvate, citric acid cycle intermediates and from most amino acids (the exceptions being leucine and lysine). The common intermediate for all of the precursors on their way to becoming glucose must be oxaloacetate. | ||
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| - | The aldolase catalyzes the reversible cleavage of fructose-1,6-bisphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GAP). Different isozymes of aldolase can also catalyze the cleavage of fructose 1-phosphate to diydroxyacetone and glyceraldehyde (GA). Different isozymes exhibit preferences for either or both of the substrates, depending on the role of the aldolase (i.e. gluconeogenesis versus glycolysis).<ref name="book">Voet, D, Voet, J, & Pratt, C. (2008). Fundamentals of biochemistry, third edition. Hoboken, NJ: Wiley & Sons, Inc.</ref> | ||
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Revision as of 14:38, 27 February 2013
Blue-green algae such as Spirulina maximize their light harvesting ability by using phycobiliproteins to absorb light over a broader spectrum. One of these proteins, allophycocyanin, can be seen on the right. It contains a chromophore called .
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Allophycocyanin is a primarily protein. It contains , which each have one phycocyanobilin. Allophycocyanin has a complex quaternary structure. First, form in a circular fashion, then on top of each other to form an antenna-like structure called the phycobilisome.
Interestingly, the λmax of the chromophore can be tuned depending upon the protein binding it. For allophycocyanin, the λmax is 650 nm; in another phycobiliprotein, phycocyanin, the λmax is 625 nm, even though it uses the same chromophore. Phycocyanobilin is a highly flexible, linear tetrapyrrole that is covalently attached to the protein by a to a cysteine in the protein. Allophycocyanin holds the in place through a number of intermolecular interactions. forms hydrogen bonds with an amine in the pigment, while interacts with a carboxylic acid that is exposed to the solvent. A key also holds the molecular planar. These interactions stabilize the pigment in the protein and hold the pigment planar. When the protein is unfolded, the pigment is no longer planar, and loses the ability to transfer red light to chlorophyll.
3D Structures of Allophycocyanin
1all – APC – Arthrospira platensis
1b33 – APC – Mastigocladus laminosus
1kn1 – APC – Porphyra yezoensis
2v8a – APC – Thermosynechococcus elongatus
2vjt – APC – Gloeobacter violaceus
3dbj - APC – Thermosynechococcus vulcanus
