CALF SPLEEN PURINE NUCLEOSIDE PHOSPHORYLASE - PURIFICATION, SEQUENCE AND CRYSTAL-STRUCTURE OF ITS COMPLEX WITH AN N(7)-ACYCLOGRANOSINE INHIBITOR

Calf spleen purine nucleoside phosphorylase was purified to homogeneit y and its amino acid sequence was determined, The complex of the enzym e with an N(7)-acycloguanosine inhibitor crystallized in the cubic spa ce group P2(1)3, with unit cell dimension a = 94.02 Angstrom and one m onomer in the asymmetric crystal unit, The biologically active trimer is formed by the crystallographic three-fold axis, The structure was s olved by molecular replacement methods, using the model of the human e rythrocyte enzyme, and refined at a resolution of 2.9 Angstrom to an R -factor of 0.21, The orientation of the inhibitor at the active site i s examined in relation to the catalytic activity of the enzyme in the phosphorolysis of N(7)-beta-D-purine nucleosides.