Regulatory properties of nucleoside phosphotransferase from mucosa of chicken intestine

Nucleoside phosphotransferase from chicken intestinal mucosa is an associated multisubunit protein which can dissociate into components of lower molecular weight. The associated and the dissociated forms have the same substrate specificity but the first (A) shows a higher V(max) and a lower S(0.5) value than the second (B), whichever phosphate donor or nucleoside acceptor was employed. Moreover with form A the interaction coefficient in the Hill plots; as measured with a phosphate donor, varied: they always showed a higher result (about 2) than with form B (about 1). A brief preincubation at 37°C of form A modified the values both of the inactivation constant and of the enzyme kinetic parameters, which became similar to those reported for form B. Form B of nucleoside phosphotransferase is, unlike form A, only moderately sensitive to the regulatory effects of nucleoside diphosphates.