Dillard W L, Graf L, Schweiger H G
Eur J Cell Biol. 1983 Jan;29(2):145-9.
The kinetic properties of UDPG pyrophosphorylase (glucosyl-1-phosphate uridyl transferase, EC 2.7.7.9) suggest that it may play a key role in the regulation of metabolism in Acetabularia mediterranea. The enzyme-catalyzed reaction is readily reversible in vitro, and has been assayed in both directions. The enzyme shows substrate inhibition by UDPG and UTP at substrate concentrations in excess of 2 mM. The kinetic behavior of the enzyme is consistent with the hypothesis that it catalyzes an ordered bisubstrate biproduct reaction in which G-1-P is the leading substrate, and UTP is the leading product. A plot of initial velocity vs. PPi concentration is sigmoid, indicating a cooperative homotropic effect. PGAL inhibits the reaction in the direction: UTP + G-1-P leads to UDPG + PPi It has no effect on the reverse reaction. The responses of the enzyme may serve to regulate the allocation of G-1-P between anabolic and catabolic pathways.
UDPG焦磷酸化酶（葡糖-1-磷酸尿苷酰转移酶，EC 2.7.7.9）的动力学特性表明，它可能在地中海伞藻的代谢调节中起关键作用。该酶催化的反应在体外很容易逆转，并且已经在两个方向上进行了测定。在底物浓度超过2 mM时，该酶表现出对UDPG和UTP的底物抑制作用。该酶的动力学行为与以下假设一致：它催化一种有序的双底物双产物反应，其中G-1-P是主要底物，UTP是主要产物。初始速度与PPi浓度的关系图呈S形，表明存在协同同促效应。PGAL在UTP + G-1-P → UDPG + PPi方向上抑制该反应。它对逆反应没有影响。该酶的这些反应可能有助于调节G-1-P在合成代谢和分解代谢途径之间的分配。
