Wildenthal K, Griffin E E, Ingwall J S
Circ Res. 1976 May;38(5 Suppl 1):I138-44.
Isolated hearts of fetal mice in organ culture maintain active protein synthesis and protein degradation. Rates of degradation exceed rates of synthesis and as a result, the hearts are in state of negative protein balance as evidenced by net loss of protein and release of amino acids. Several hormones can alter amino acid metabolism and protein balance by altering synthesis or degradation, or both. In cultured fetal mouse hearts, insulin, the most extensively studies of the hormones increases the rate of protein synthesis by 13 +/- 3.7% and decreases the rate of protein degradation by 22 +/- 4.1% (p less than 0.01 for both). Together, these changes account for a 30-40% reduction in the loss of cardiac protein and in the release of phenylalanine from the heart. These changes are accompanied by a decrease of 21 +/- 2.7% in the total activity of the lysosomal proteinase cathepsin D. and by a reduction in the proportion of the enzyme that is present in the nonsedimentable fraction of the issue homogenate. This suggests that the possibility that insulin may function in part by altering lysosomal enzyme activity or availability, or both. The effects of insulin on protein degradation, amion acid release, and cathepsin D activity persist even when protein synthesis has been inhibited by cycloheximide. These results suggest that insulin plays an important role in the control of cardiac protein synthesis and degradation.
器官培养中分离出的胎鼠心脏维持着活跃的蛋白质合成和蛋白质降解。降解速率超过合成速率，因此，心脏处于蛋白质负平衡状态，这表现为蛋白质净损失和氨基酸释放。几种激素可通过改变合成或降解，或两者皆改，来改变氨基酸代谢和蛋白质平衡。在培养的胎鼠心脏中，胰岛素是对激素研究最广泛的一种，它使蛋白质合成速率提高了13±3.7%，并使蛋白质降解速率降低了22±4.1%（两者p均小于0.01）。这些变化共同导致心脏蛋白质损失和心脏中苯丙氨酸释放减少30 - 40%。这些变化伴随着溶酶体蛋白酶组织蛋白酶D的总活性降低21±2.7%，以及该酶在组织匀浆不可沉淀部分中所占比例的降低。这表明胰岛素可能部分通过改变溶酶体酶活性或可用性，或两者兼而有之来发挥作用。即使蛋白质合成已被放线菌酮抑制，胰岛素对蛋白质降解、氨基酸释放和组织蛋白酶D活性的影响仍然存在。这些结果表明胰岛素在心脏蛋白质合成和降解的控制中起重要作用。
