Use of the integrated steady state rate equation to investigate product inhibition of human red cell adenosine deaminase and its relevance to immune dysfunction.

W.R Osborne,S.H Chen,C.R Scott

doi:10.1016/s0021-9258(17)38204-2

W.R Osborne, S.H Chen + Show 1 more

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https://doi.org/10.1016/s0021-9258(17)38204-2

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Abstract

The analysis of progress curves using the integrated rate equation was applied to the adenosine deaminase-catalyzed conversion of adenosine to inosine. Adenosine deaminase was purified from human red blood cells of phenotypes ADA 1, ADA 2, and ADA 2-1. For all three types, no measurable product inhibition by inosine was observed. These results do not confirm the hypothesis that inosine accumulation in purine nucleoside phosphorylase deficiency causes adenosine deaminase inhibition, resulting in a common mechanism for the immune defects related to these two enzyme deficiencies.

Highlights

These results do not confirm the hypothesis that inosine accumulation in purine nucleoside phosphorylase deficiency causes adenosine deaminase inhibition, resulting in a common mechanism for the immune defects related to these two enzyme deficiencies
In the system of purine reutilization, the inosine produced by the adenosine deaminase reaction is converted to hypoxanthine and ribose l-phosphate by the enzyme purinenucleoside phosphorylase (EC 2.4.2.1) [4]
Progress Curves -Experiments using the three purified adenosine deaminase phenotypes were conducted with initial substrate concentrations of 60, 90, and 120 PM in 0.1 M phosphate buffer, pH 7.0, and human serum albumin at a final concentration of 0.1 mglml

Summary

Introduction

These results do not confirm the hypothesis that inosine accumulation in purine nucleoside phosphorylase deficiency causes adenosine deaminase inhibition, resulting in a common mechanism for the immune defects related to these two enzyme deficiencies. The analysis of progress curves using the integrated rate equation [13, 14] is not subject to this limitation and was used to test for any product inhibition of the adenosine deaminase reaction. Heat Denaturation -The first order rate constants for heat denaturation of a purified ADA 1 preparation, with and without the addition of various amounts of human serum albumin, were performed at 54” in 0.1 M phosphate buffer, pH 7.0.

Results

Conclusion