Malaisse-Lagae F, Zähner D, Malaisse W J
Laboratory of Experimental Medicine, Erasmus Medical School, Brussels Free University, Belgium.
Int J Biochem Cell Biol. 1995 Sep;27(9):905-9. doi: 10.1016/1357-2725(95)00064-v.
The present study explores the possible channelling of pyruvate generated by either pyruvate kinase or NADP-malate dehydrogenase to lactate dehydrogenase in cross-linked and permeabilized erythrocytes. The generation of both unlabelled and 14C-labelled pyruvate and lactate was measured in rat erythrocytes, which were prepared for cross-linking with dimethyl suberimidate and permeabilization by digitonin and then exposed to unlabelled or 14C-labelled malate and/or phospho-enol-pyruvate. Rat erythrocytes were found to display NADP-malate dehydrogenase activity. Under conditions in which the generation rates of pyruvate from either phospho-enol-pyruvate (15 microM) or malate (0.5 mM) were not vastly different from one another, a greater fraction of the 2-keto acid was converted to lactate when produced from phospho-enol-[1-14C]pyruvate rather than [U-14C]malate. This difference was most obvious when the availability of exogenous NADH was close to or somewhat below that theoretically required to ensure full conversion of endogenously formed pyruvate to lactate. These findings are compatible with the view that pyruvate generated at the pyruvate kinase level is converted to lactate more efficiently than pyruvate produced in the reaction catalysed by NADP-malate dehydrogenase.
本研究探讨了在交联和透化的红细胞中，由丙酮酸激酶或NADP-苹果酸脱氢酶产生的丙酮酸可能向乳酸脱氢酶的传递途径。在大鼠红细胞中测定了未标记和14C标记的丙酮酸和乳酸的生成情况，这些红细胞用辛二酸二甲酯进行交联，并用洋地黄皂苷进行透化处理，然后暴露于未标记或14C标记的苹果酸和/或磷酸烯醇丙酮酸。发现大鼠红细胞具有NADP-苹果酸脱氢酶活性。在磷酸烯醇丙酮酸（15 microM）或苹果酸（0.5 mM）产生丙酮酸的速率彼此差异不大的条件下，当由磷酸烯醇-[1-14C]丙酮酸而非[U-14C]苹果酸产生2-酮酸时，更大比例的2-酮酸被转化为乳酸。当外源性NADH的可用性接近或略低于理论上确保内源性生成的丙酮酸完全转化为乳酸所需的水平时，这种差异最为明显。这些发现与以下观点一致，即丙酮酸激酶水平产生的丙酮酸比NADP-苹果酸脱氢酶催化的反应中产生的丙酮酸更有效地转化为乳酸。
