A comparison of the kinetic properties of the common and rare variants of adenosine deaminase

Adenosine deaminase activity has been measured in red cells from individuals of known ADA phenotype (ADA 1, ADA 2-1, ADA 3-1, ADA 3-2) using adenosine and 2'-deoxyadenosine as substrates. No significant differences were observed among the phenotypes in their relative deaminase activity with the two substrates. However, evidence suggests the occurrence of an uncommon allele designated ADA1w determining low levels of ADA activity. The deaminase activities of the phenotypes were in the order ADA 1 greater than ADA 2-1 greater than ADA 3-1 greater than ADA 3-2 with both substrates. The relative activities of the alleles were estimated to be: ADA1 100%, ADA2 89%, ADA3 28% and ADA1w 67% with adenosine, and ADA1 100%, ADA2 87%, ADA3 39% and ADA1w 66% with 2'-deoxyadenosine. The Michaelis constants for adenosine and 2'-deoxyadenosine were determined for the different phenotypes. There were no significant differences in these values among the phenotypes.