Foster J D, Nelson K L, Sukalski K A, Lucius R W, Nordlie R C
Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine, Grand Forks 58202.
Biochim Biophys Acta. 1991 Dec 11;1118(1):91-8. doi: 10.1016/0167-4838(91)90445-6.
Carbamyl-P:glucose and PPi:glucose phosphotransferase, but not inorganic pyrophosphatase, activities of the hepatic microsomal glucose-6-phosphatase system demonstrate a time-dependent lag in product production with 1 mM phosphate substrate. Glucose-6-P phosphohydrolase shows a similar behavior with [glucose-6-P] less than or equal to 0.10 mM, but inorganic pyrophosphatase activity does not even at the 0.05 or 0.02 mM level. The hysteretic behavior is abolished when the structural integrity of the microsomes is destroyed by detergent treatment. Calculations indicate that an intramicrosomal glucose-6-P concentration of between 20 and 40 microM must be achieved, whether in response to exogenously added glucose-6-P or via intramicrosomal synthesis by carbamyl-P:glucose or PPi:glucose phosphotransferase activity, before the maximally active form of the enzyme system is achieved. It is suggested that translocase T1, the transport component of the glucose-6-phosphatase system specific for glucose-6-P, is the target for activation by these critical intramicrosomal concentrations of glucose-6-P.
氨基甲酰 - P：葡萄糖和焦磷酸：葡萄糖磷酸转移酶，而非无机焦磷酸酶，肝脏微粒体葡萄糖 - 6 - 磷酸酶系统的活性在以1 mM磷酸盐为底物时，产物生成呈现出时间依赖性滞后。葡萄糖 - 6 - 磷酸水解酶在[葡萄糖 - 6 - 磷酸]小于或等于0.10 mM时表现出类似行为，但无机焦磷酸酶活性即使在0.05或0.02 mM水平也未出现这种情况。当通过去污剂处理破坏微粒体的结构完整性时，滞后行为消失。计算表明，无论是对外源性添加的葡萄糖 - 6 - 磷酸做出反应，还是通过氨基甲酰 - P：葡萄糖或焦磷酸：葡萄糖磷酸转移酶活性进行微粒体内合成，在达到酶系统的最大活性形式之前，必须使微粒体内葡萄糖 - 6 - 磷酸浓度达到20至40 microM之间。有人提出，转位酶T1，即葡萄糖 - 6 - 磷酸酶系统中对葡萄糖 - 6 - 磷酸具有特异性的转运成分，是这些关键的微粒体内葡萄糖 - 6 - 磷酸浓度激活的靶点。
