成年微小膜壳绦虫（绦虫纲）中的磷酸烯醇丙酮酸分支点：丙酮酸激酶和磷酸烯醇丙酮酸羧激酶的研究

The phosphoenol-pyruvate branchpoint in adult Hymenolepis diminuta (Cestoda): a study of pyruvate kinase and phosphoenol-pyruvate carboxykinase.

作者信息

Moon T W, Mustafa T, Hulbert W C, Podesta R B, Mettrick D F

出版信息

J Exp Zool. 1977 Jun;200(3):325-36. doi: 10.1002/jez.1402000303.

DOI:10.1002/jez.1402000303

Abstract

The properties of pyruvate kinase (PK) and phosphoenol pyruvate carboxykinase (PEP CK), two enzymes that determine the preferrential accumulation of either succinate or lactate as endproducts of carbohydrate metabolism, are described in adult Hymenolepis diminuta. PK activity at Vmax and Km levels of PEP was unaffected by ATP, alanine, FDP4, OR H+ ions, but was inhibited by 50% at 6.3 mM L-lactate and 30 mM HCO3. The addition of 30 mM HCO3 increased the Km(PEP) by 6-fold but did not alter the Vmax. The inhibition of PK by HCO3 cannot be explained entirely by an effect of ionic strength, but probably represents a specific modulator-enzyme interaction. Under similar conditions PEP CK was maximally activated. Although L-lactate inhibited PEP CK (Ki(lac) = 1.8 mM), this effector may play a minor role in regulation of PEP flux. These results implicate the poise of the HCO3-:CO2 system as a major determiner of endproduct accumulation in H. diminuta.

摘要

本文描述了成年微小膜壳绦虫中丙酮酸激酶（PK）和磷酸烯醇丙酮酸羧激酶（PEP CK）这两种酶的特性，这两种酶决定了碳水化合物代谢终产物琥珀酸或乳酸的优先积累。PEP的Vmax和Km水平下的PK活性不受ATP、丙氨酸、FDP4或H⁺离子的影响，但在6.3 mM L-乳酸和30 mM HCO₃存在时被抑制50%。添加30 mM HCO₃可使Km（PEP）增加6倍，但不改变Vmax。HCO₃对PK的抑制不能完全用离子强度的影响来解释，可能代表一种特定的调节物-酶相互作用。在类似条件下，PEP CK被最大程度激活。虽然L-乳酸抑制PEP CK（Ki（lac）= 1.8 mM），但这种效应物在调节PEP通量中可能起次要作用。这些结果表明，HCO₃⁻:CO₂系统的平衡是微小膜壳绦虫终产物积累的主要决定因素。