Scholz T D, Koppenhafer S L, tenEyck C J, Schutte B C
Department of Pediatrics, University of Iowa, Iowa City 52242, USA.
Am J Physiol. 1998 Mar;274(3):C780-8. doi: 10.1152/ajpcell.1998.274.3.C780.
Developmental downregulation of the malate-aspartate shuttle has been observed in cardiac mitochondria. The goals of this study were to determine the time course of the postnatal decline and to identify potential regulatory sites by measuring steady-state myocardial mRNA and protein levels of the mitochondrial proteins involved in the shuttle. By use of isolated porcine cardiac mitochondria incubated with saturating concentrations of the cytosolic components of the malate-aspartate shuttle, shuttle capacity was found to decline by approximately 50% during the first 5 wk of life (from 921 +/- 48 to 531 +/- 53 nmol.min-1.mg protein-1). Mitochondrial aspartate aminotransferase mRNA levels were greater in adult than in newborn myocardium. mRNA levels of mitochondrial malate dehydrogenase in adult cardiac tissue were 224% of levels in newborn tissue, whereas protein levels were 54% greater in adult myocardium. Aspartate/glutamate carrier protein levels were also greater in adult than in newborn tissue. mRNA and protein levels of the oxoglutarate/malate carrier were increased in newborn myocardium. It was concluded that 1) myocardial malate-aspartate shuttle capacity declines rapidly after birth, 2) divergence of mitochondrial malate dehydrogenase mRNA and protein levels during development suggests posttranscriptional regulation of this protein, and 3) the developmental decline in malate-aspartate shuttle capacity is regulated by decreased oxoglutarate/malate carrier gene expression.
在心脏线粒体中已观察到苹果酸-天冬氨酸穿梭的发育性下调。本研究的目的是确定出生后下降的时间进程，并通过测量参与该穿梭的线粒体蛋白的心肌mRNA和蛋白质稳态水平来确定潜在的调控位点。通过使用与苹果酸-天冬氨酸穿梭的胞质成分饱和浓度孵育的分离猪心脏线粒体，发现穿梭能力在生命的前5周内下降了约50%（从921±48降至531±53 nmol·min-1·mg蛋白-1）。成人心肌中线粒体天冬氨酸转氨酶的mRNA水平高于新生心肌。成年心脏组织中线粒体苹果酸脱氢酶的mRNA水平是新生组织中的224%，而成人心肌中的蛋白质水平高54%。天冬氨酸/谷氨酸载体蛋白水平在成体中也高于新生组织。新生心肌中氧代戊二酸/苹果酸载体的mRNA和蛋白质水平增加。得出的结论是：1）出生后心肌苹果酸-天冬氨酸穿梭能力迅速下降；2）发育过程中线粒体苹果酸脱氢酶mRNA和蛋白质水平的差异表明该蛋白存在转录后调控；3）苹果酸-天冬氨酸穿梭能力的发育性下降是由氧代戊二酸/苹果酸载体基因表达降低所调节的。
