Schwartz C F, Carter C E
J Parasitol. 1982 Apr;68(2):228-35.
Glycogen synthase and phosphorylase were characterized from the cephalopedal region of the snail, Biomphalaria glabrata. Glycogen synthase exhibited increases and decreases in its activity ratio (-G6P/+G6P) under conditions that are known to cause conversion of the two forms of the enzyme from mammalian systems, implying that the snail's synthase also possesses interconvertible forms. Each form had a distinct pH optimum, with the G6P-independent form (synthase alpha) exhibiting maximum activity at pH 7.4, whereas the G6P-dependent form (synthase beta) had optimal activity at pH 8.3. Both synthase alpha and beta displayed classical Michaelis-Menten kinetics for the substrates UDP-glucose and glycogen, and the beta form displayed sigmoidal kinetics for its modulator, G6P. Only UDP-glucose could function as a glucosyl donor in the synthase-catalyzed reaction. ADP, GDP, UDP, and ATP were all competitive inhibitors of synthase alpha, although at varying degrees of efficiency. Glycogen phosphorylase also demonstrated interconversion of its two forms (alpha and beta), as evidenced by changes in its activity ratio (-AMP/+AMP). AMP elicited hyperbolic kinetics from this enzyme. Concentrations of KF above 20 mM were found to inhibit glycogen synthase alpha while stimulating phosphorylase beta, thus causing erroneous activity ratios for both enzymes.
从光滑双脐螺的头足部区域对糖原合酶和磷酸化酶进行了表征。在已知会导致哺乳动物系统中该酶两种形式发生转化的条件下，糖原合酶的活性比（-G6P/+G6P）出现升高和降低，这意味着蜗牛的合酶也具有可相互转化的形式。每种形式都有一个独特的最适pH值，不依赖G6P的形式（合酶α）在pH 7.4时表现出最大活性，而依赖G6P的形式（合酶β）在pH 8.3时具有最佳活性。合酶α和β对底物UDP-葡萄糖和糖原均表现出典型的米氏动力学，并且β形式对其调节剂G6P表现出S形动力学。在合酶催化的反应中，只有UDP-葡萄糖可以作为葡萄糖基供体。ADP、GDP、UDP和ATP都是合酶α的竞争性抑制剂，尽管抑制效率各不相同。糖原磷酸化酶也表现出其两种形式（α和β）的相互转化，这通过其活性比（-AMP/+AMP）的变化得以证明。AMP使该酶呈现双曲线动力学。发现KF浓度高于20 mM时会抑制糖原合酶α，同时刺激磷酸化酶β，从而导致两种酶的活性比出现错误。
