title: Co-operativity in seminal ribonuclease function: binding studies.
abstract: Binding of nucleotides to bovine seminal RNAase was studied by differential spectrophotometry and equilibrium dialysis. Cytidine 3'-phosphate, the reaction product of the hydrolytic, rate-limiting step of the reaction, was found to be capable, in contrast to related nucleotides, of discriminating between the two structurally identical active sites of the enzyme. Negative co-operativity, with a 'half-of-sites' reactivity, was found at lower concentrations of ligand, whereas at higher concentrations positive co-operativity was detected. These findings exclude that the non-hyperbolic kinetics previously reported for the hydrolytic step of the reaction are due to hysteretic effect. A model of mixed-type co-operativity is proposed for interpreting the binding data.
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003568:Cytidine Monophosphate / Q000378:metabolism; D003956:Dialysis; D007536:Isomerism; D007700:Kinetics; D008297:Male; D008956:Models, Chemical; D011485:Protein Binding; D012260:Ribonucleases / Q000378:metabolism*; D012661:Semen / Q000201:enzymology*; D013053:Spectrophotometry
chemical_list: D000249:Adenosine Monophosphate; D012260:Ribonucleases; D003568:Cytidine Monophosphate