Kinetic properties of the common electrophoretic variants of human S-adenosylhomocysteine hydrolase (AHCY): the effect of four nucleoside analogue inhibitors

Red blood cell S-adenosylhomocysteine hydrolase (AHCY) from individuals of 1, 2-1 and 3-1 phenotypes was partially purified and K _m and V _max determined in the absence and in the presence of the following inhibitors: 3-deaza-adenosine (DZA), 3-deaza-aristeromycin (DZAry), 2–chloro adenosine (2-Cl-ado) and purine riboside (or nebularine). The three phenotypes 1, 2-1, 3-1 showed similar K _m (32·58, 39·22 and 34·84 μ m respectively), but the ratio K _m/ V _max was statistically different. DZA and DZAry appeared to be strong competitive inhibitors. The AHCY 1 phenotype was more resistant to their action, while the 3-1 variant was more sensitive. 2-Cl-ado and purine riboside were weaker inhibitors; the type of inhibition varied among the three phenotypes, but, again, the AHCY 1 phenotype was less sensitive than the other two.