Incorporation of C¹⁴-amino acids into protein of isolated diaphragms: an effect of insulin independent of glucose entry

Abstract

The effect of glucose concentration and insulin on protein synthesis was investigated using the isolated rat diaphragm and C14-labeled amino acids. When the donor rat has been well fed, the incorporation of histidine-2-C14, lysine-2-C14, phenylalanine-3-C14, and alanine-1-C14 into muscle protein is uninfluenced by glucose concentration in the medium over the range 0–600 mg %. Insulin leads to an increase in C14-amino acid incorporation into muscle protein in the absence of glucose in the medium. This positive effect of insulin in the absence of added glucose is still observed when the diaphragms are pre-incubated for 2 hours prior to adding insulin. These findings suggest an effect of insulin on protein metabolism independent of its action in promoting glucose entry.

Effects of insulin on ovine fetal leucine kinetics and protein metabolism.

“…Evaluation of fetal protein metabolism requires measurement of two of the three variables related as follows: Synthesis = breakdown + accretion (growth) (1) The following formulas were therefore used to estimate the rate offetal protein synthesis. Synthesis (nonoxidative disposal) = leucine disposal -leucine decarboxylation, where leucine disposal was defined as:…”

“…In vitro studies have shown that insulin promotes both amino acid uptake (1) and protein breakdown in rat muscle (2). In vivo, however, insulin's effects are somewhat different.…”

Metabolic and Ultrastructural Changes Induced in Adipose Tissue by Insulin

“…Not the least of these components might be those that comprise the cell's surface membrane which, as a result of vesicle formation, might be undergoing constant renewal. In this connection it should be noted that the addition of insulin in vitro has been found to increase the rate of incorForation of labeled amino acids into proteins (40)(41)(42)(43) and of radioactive phosphorus into phospholipids and nucleic acids (35). In the case of amino acid incorporation into protein, the accelerating action of insulin has been demonstrated under conditions in which an increased entry of the amino acid into the tissue has been excluded as an explanation for this effect (43).…”

The Impact of Streptozotocin-induced Diabetes Mellitus on Cyclic Nucleotide Regulation of Skeletal Muscle Amino Acid Metabolism in the Rat

“…This may be contributed by the catabolism of other, protein-derived amino acids, b)y pyruvate formed by glycolysis, or by a combination of 1)oth processes (4,(7)(8)(9)(10)(11)(12)(13). Because insuilini promiiotes mutscle protein synthesis and also inhibits mutscle protein degradation (14)(15)(16), increased alatnine release wotuld be expected in an insulin deficiency state stuch as diabetes mellitts. However, the impact of the diabetic state on otlher, noninstulin-dependent mechanismiis that regulate inmuscle protein and aiiiino acid metabolism hals not been investigated in detail.…”