The cost of enzyme synthesis in the genetics of energy balance and physiological performance

Abstract

The study of metabolism has traditionally focused upon factors that influence metabolic rate, at levels of both the metabolic pathway and the whole organism. This paper focuses on the cost, and thereby the efficiency, of metabolic processes. The genotype-dependent cost of enzyme turnover is proposed as a biochemical genetic mechanism for relating genetic variation at single genes to phenotypic variation in quantitative traits of energy metabolism. Decreased costs of maintenance metabolism can accompany artificial selection for increased production (e.g. growth, reproduction, etc.) and lower maintenance is correlated with multiple locus heterozygosity in outbred populations. In both cases, high production has been associated with lower rates of protein turnover. Several factors influence the ATP-equivalent cost of enzyme turnover. These factors are used to calculate the cost of turnover for a single enzyme. This cost can conservatively constitute up to several percent of the total daily mass-specific energy demands of maintenance metabolism. Genetic variants of an enzyme can differ in the cost of turnover. These differences can constitute the basis for metabolic changes associated with artificial selection for production and the metabolic differences that are associated with individual levels of heterozygosity. The metabolic and evolutionary significance of genotype-dependent turnover costs is a function of individual energy balance. The strength of selection against increases in cost will be an inverse function of individual energy balance and is therefore influenced by both environmental and genetic factors.KEY WORDS:-Energy metabolism -protein turnover ~ enzyme synthesis -polymorphisrnmaintenance-heterozygosity.

Lipid remodeling in wild and selectively bred hard clams at low temperatures in relation to genetic and physiological parameters

“…For example, mussel stocks susceptible to summer mortality had a lower degree of heterozygosity and showed higher oxygen consumption rates than mussels from resistant stocks, thus suggesting that the energy expenditure for maintenance was higher for mussels from susceptible stocks (Tremblay et al, 1998;Myrand et al, 2002). These results are in agreement with several other studies on molluscs that indicated that more heterozygous individuals show more efficient protein synthesis and a higher scope for growth compared to more homozygous individuals (Hawkins et al, 1989), which results in higher growth and survival rates (Zouros and Foltz, 1987;Koehn, 1991;Mitton, 1993). There are similarities between our study and previous work done on mussels: there is high seasonal mortality, populations are characterized by a heterozygote deficit, and relationships exist between the genetic make-up and physiology.…”

Linking Post-Translational Modifications and Variation of Phenotypic Traits

“…At this stage the enzymatic pool allocated to the fermentation proteome, which represents one third of the total proteome, appeared to be constant over the media and strains considered. Previous work has suggested that enzyme concentrations cannot increase indefinitely and are probably bounded because of cellular constraints in space and energy (55), avoiding macromolecular crowding (56) and lowering the energetic cost associated with enzyme transcription, translation, and maintenance under limited resources (57,58). Although our data demonstrated the existence of such a constraint at the level of the whole fermentation proteome, we have also shown that the AF enzymes have reduced variance compared with non-AF proteins, highlighting the existence of evolution- FIG.…”

Enzyme heterozygosity, metabolism, and developmental stability

“…The half-life of soluble enzymes is on the order of 24 h (Koehn, 1991), so that many of the thousands of enzymes needed to control metabolism must be replaced each day. Consequently, a substantial portion of basal metabolic cost, perhaps 20% to 40%, is spent to break down damaged proteins and synthesize new proteins.…”