Purine nucleoside phosphorylase polymorphism in sheep erythrocytes

A polymorphism of purine nucleoside phosphorylase is described in sheep erythrocytes. Two isozymes were distinguished electrophoretically, one with high activity (NP-1) and one with low activity (NP-2). Breeding data suggest that the two isozymes are the product of two codominant alleles, NP1 and NP2. The Km's for inosine did not differ between NP-1 and NP-2; however, NP-2 had a lower pH optimum and was relatively unstable when incubated at 48 C.