The enzymes of lactose biosynthesis I. Purification and properties of UDPG pyrophosphorylase from bovine mammary tissue

Abstract

UDPG pyrophosphorylase (UTP:α-d-glucose-1-phosphate uridyltransferase EC 2.7.7.9) has been purified from bovine mammary gland acetone powder. The enzyme is specific for UTP and glucose 1-phosphate. The enzyme is inhibited by anions and galactose 1-phosphate is a competitive inhibitor, $\text{K}{}_{\mathrm{i}}\text{= 8·10}{}^{\mathrm{-3}}\text{M}$. The enzyme requires Mg²⁺ for activity. The $\text{K}{}_{\mathrm{m}}$ for all the substrates have been determined and they are a function of the Mg²⁺ concentration. The pH optimum is between 8 and 9.