Measuring in vivo intracellular protein degradation rates in animal systems

¹ Program in Cellular and Molecular Biosciences, Department of Animal Sciences, Auburn University, AL 36849-5415

^* To whom correspondence should be addressed. E-mail: bergewg{at}auburn.edu.

	Abstract

Continual synthesis and breakdown or remodeling of proteins (also called protein turnover) is a principal characteristic of protein metabolism. During animal production, the net differences between synthesis and breakdown represent the actual marketable muscle foods. Because protein synthesis is a highly endergonic and protein breakdown is metabolic energy-dependent as well, efficiency of production can be markedly enhanced by lower muscle protein breakdown rates. Herein various methodological approaches to studying protein breakdown, with particular emphasis toward food producing animals, are presented. These include whole animal tracer amino acids infusions in vivo, quantifying marker amino acid release from muscle proteins, and in vitro amino acid release-based methodologies. From such methods, protein synthesis rates and protein breakdown rates (mass units/time) may be obtained. The applications of such methods and new innovations based on traditional methods are discussed. Whole animal, in vivo approaches are resource intensive and often not easily applied to high throughput, metabolic screening. Over the last twenty five years, biochemical mechanisms and molecular regulation of protein biosynthesis and protein breakdown have been extensively documented. Proteolysis is dependent in part on the extent of expression of genes for components of cellular proteolytic machinery during skeletal muscle atrophy. It is proposed that high throughput methods, based on emerging understanding about protein breakdown, may be useful in enhancing production efficiency.

Key Words: Marker amino acids, proteolysis, protein synthesis, tracer methodology, transcriptional and translational control, ubiquitin-proteasome