Document Type
Article
Publication Date
11-2005
Keywords
coproporphyrinogen oxidase, porphyria, Km, Kcat, substrate analog, ABNORMAL HEME-BIOSYNTHESIS, ACTIVE-SITE, METABOLISM, PORPHYRIAS, IV, Research & Experimental Medicine
Abstract
Background: The enzyme coproporphyrinogen oxidase (copro'gen oxidase) converts coproporphyrinogen-Ill (GIII) to protoporphyrinogen-IX via an intermediary monovinyl porphyrinogen. The A ring isomer coproporphyrinogen-IV (C-IV) has previously been shown to be a substrate for copro'gen oxidase derived from avian erythrocytes. In contrast to the authentic substrate (GIII) where only a small amount of the monovinyl intermediate is detected, C-IV gives rise to a monovinyl intermediate that accumulates before being converted to an isomer of protoporphyrinogen-IX. No kinetic studies have been carried out using the purified human copro'gen oxidase to evaluate its ability to process both the authentic substrate as well as analogs. Material/Methods: Therefore, purified, cloned human copro'gen oxidase was incubated with GIII or C-IV at 37 degrees C with various substrate concentrations (from 0.005 mu M to 3.5 mu M). The Km (an indication of molecular recognition) and Kcat (turnover number) values were determined. Results: The Km value for total product formation was about the same with either C-III or C-IV indicating the same molecular recognition. However, the catalytic efficiency (Kcat/Km) of the enzyme for total product formation was not more than two fold higher using GIII relative to C-IV. Conclusions: Since the Km values are about the same for either substrate and the total Kcat/Km values are within two fold of each other, this could correlate with the increase of severity of porphyrias with monovinyl accumulation. The ability of the increased levels of C-IV to compete with the authentic substrate has important implications for clinical porphyrias.
Recommended Citation
Jones, Marjorie A.; Cooper, Christopher L.; and Lash, Timothy D., "Kinetic evaluation of human cloned coproporphyrinogen oxidase using a ring isomer of the natural substrate" (2005). Faculty Publications – Chemistry. 1.
https://ir.library.illinoisstate.edu/fpchem/1
Comments
This article is the copyright property of the Medical Science Monitor and may not be used for any commercial or other private purpose without specific written permission of the Medical Science Monitor.