Molecular properties and a nonidentical trimeric structure of purine nucleoside phosphorylase from chicken liver

Some molecular properties of crystalline purine nucleoside phosphorylase (purine nucleoside: orthophosphate ribosyltransferase, EC 2.4.2.1) from chicken liver were investigated and discussed. The molecular weight of the native enzyme was determined to be 89 000 by gel filtration and sedimentation coefficient, and 90 000 by sedimentation equilibrium, respectively. The enzyme was assumed to be a trimer consisting of one large subunit and two identical small subunits. The molecular weights of two different sized subunits were determined to be 32 000 and 28 000 by sodium dodecyl sulfate gel electrophoresis, and 30 000 and 27 000 by 6 M guanidine hydrochloride gel filtration. The amino acid composition was determined and the partial specific volume was estimated to be 0.735 ml/g.