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Publication Abstract from PubMed

X-ray crystal structures of dehaloperoxidase-hemoglobin A (DHP A) from Amphitrite ornata soaked with substrate, 2,4,6-tribromophenol (2,4,6-TBP), in buffer solvent with added methanol (MeOH), 2-propanol (2-PrOH) and dimethylsulfoxide (DMSO) reveal an internal substrate binding site deep in the distal pocket above the -edge of the heme that is distinct from the previously determined internal inhibitor binding site. The peroxidase function of DHP A has most often been studied using 2,4,6-trichlorophenol (2,4,6-TCP) as a substrate analog because of the low solubility of 2,4,6-TBP in aqueous buffer solution. Previous studies at low substrate concentration pointed towards the binding of substrate 2,4,6-TCP at an external site near the exterior heme - or -edge as observed in the class of heme peroxidases. Here we report that the turnover frequencies of both substrates 2,4,6-TCP and 2,4,6-TBP deviate from Michaelis-Menten kinetics at high concentration. The turnover frequency reaches a maximum in the range 1400-1700 M with a decrease in rate at higher concentrations that is both substrate and solvent dependent. The X-ray crystal structure is consistent the presence of an internal active site above the heme -edge, in which the substrate would be oxidized in two consecutive steps inside the enzyme, followed by attack by H2O via a water channel in the protein. The physiological role of the internal site may involve interactions with any of a number of aromatic toxins found in benthic ecosystems where A. ornata resides.

Structural and kinetic study of an internal substrate binding site of dehaloperoxidase-hemoglobin A from Amphitrite ornata.,Zhao J, de Serrano VS, Zhao J, Le PD, Franzen S Biochemistry. 2013 Mar 12. PMID:23480178^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.