Catabolism and synthesis of amino acids in skeletal muscle: their significance in monogastric mammals and ruminants

Abstract

The enhanced rate of synthesis and catabolism of amino acids in, and their release from, skeletal muscle, particularly during fasting, exercise and metabolic acidosis, highlight the integrative role of muscle in protein-energy metabolism. This review discusses aspects of such changes in muscles of monogastric mammals and ruminants. The glucose-alanine cycle, as it was originally proposed, has been well substantiated by studies using human and rat muscles. An alternative proposal, which suggested that other amino acids make a major contribution to the carbon skeleton of alanine synthesized in muscle, is less convincing, since some of the inhibitors and substrates used in relevant studies have been demonstrated to have multiple rather than specific effects. In the ruminant, the glucose-alanine cycle is quantitatively less significant than in human. The probable reason for this difference is the limited available pyruvate in ruminant muscle for transamination to alanine. This may be due to a lower carbon flux through the glycolytic pathway and/or to significant activity of the anaplerotic enzyme, pyruvate carboxylase. It is suggested that glutamine is the more important carrier of carbon and nitrogen out of skeletal muscle and that alanine may serve only as an ancillary vehicle to transport carbon and nitrogen when the availability of pyruvate for transamination in muscle is high. The more diverse role of glutamine (cf. alanine) in acid-base balance, as a respiratory fuel in the cells of the immune system and the epithelia of the small intestine, where it may also be converted to alanine for subsequent gluconeogenesis in the liver, is consistent with this suggestion.

Effect of Feeding Alfalfa and Concentrate on Meat Quality and Bioactive Compounds in Korean Native Black Goat Loin during Storage at 4°C

“…Increased histidine: lysine ratios (0.64) and histidine contents in diet increased the carnosine and anserine contents in chicken muscle and blood ( Lackner et al, 2021 ). Although goats (ruminant) have a different amino acid metabolism than chickens (monogastric) ( Teleni, 1993 ; Vernon, 1980 ), we postulated that the high histidine: lysine ratio in the concentrate (0.51; Zhang et al, 2020 ) helps improve the histidine-dipeptide contents in loin meat from the KLA group, compared to that in alfalfa (0.36; Kaldy et al, 1980 ). However, further analysis is required to evaluate the effect of histidine supplementation on carnosine and anserine contents, as well as the underlying metabolic mechanism in goat meat.…”

Quantitative aspects of blood and amino acid flows in cattle

“…It accounts for 25% of the whole body 0 2 -uptake while the liver itself represents only 1.5% of total body mass in lactating cows (Huntington, 1990 (Teleni, 1993). It therefore appears necessary to study the net amino acid release by muscle tissues in order to predict the quantity available for other organs.…”

Gastric digestion of protein through pancreozyme action optimizes intestinal forms for absorption, mucin formation and villus integrity

“…Glutamine is the most abundant amino acid in circulation and maintained by degradation of muscle proteins which can be substantial by virtue of available mass (Change and Goldberg 1978;Teleni, 1993 the Kreb's cycle forms glutamic acid which then leads to glutamine by via glutamine synthetase (Wu and Thompson, 1987a,b;Wu et al, 1989;Thompson and Wu, 1991). The by-product ketone body (2-oxoisocaproate, KIC) is also released to serve as an energy source for the mucosa and complement glutamine.…”