Author(s): SHEN KUNG-MOU SHEN YUEN-KANG
Pages: 185-189
Year: 1957 Issue:  2
Journal: Acta Physiologica Sinica
Keyword:  磷酸化酶; 抑制作用; 作用速度; 淀粉酶; 引子; 酶作用; 主要作用; 酶分解; 不同来源; 溶液;
Abstract: It is wellknown that the phosphorylase activity in starch synthesis requires the presence of certain amount of starch as primer and that β-amylase has powerful ability to hy- drolyze starch.If both enzymes are present and the concentration of starch is low,the reaction rate of phosphorylase will be retarded by the destruction of the primer.Porter claimed that,be- sides primer destruction,β-amylase exerts a direct inhibitory action on phosphorylase.But her evidence was not conclusive.The experiments were repeated under conditions similar to that used by Porter,but with varying concentrations of starch and β-amylase.It was found that: (1)While the reaction rate of phosphorylase is retarded to different degrees by different concentrations of β-amylase,it can be partially or fully restored by increasing the initial starch concentration in the digest.The higher the concentration of β-amylase present in the digest,the greater is the starch concentration needed to restore the reaction rate of phosphorylase(Fig.1). (2)If the experiments are carried out under a definite β-amylase concentration and varying starch concentration,the retardation of phosphorylase reaction begins to appear progressively later with increasing starch concentration.The initial reaction rate of phosphorylase is exactly the same in all cases(Fig.2). From the results obtained it is obvious that the“inhibition”of phosphorylase by β-amylase can be fully accounted for by the destruction of the starch primer.Porter's experimental results can be completely explained by this mechanism together with the presence of α-amylase in the phosphorylase preparation.