The Relevance of Whole-Body Protein Metabolism to Measured Costs of Maintenance and Growth in Mytilus edulis

Publisher Website
Google Scholar
Abstract
Protein synthesis, heat loss, and the deposition of protein and nonprotein substrates within tissue and shell were measured directly and shown to co-vary in significant positive relations with experimentally controlled rates of energy intake in mussels supplied a diet of the same proximate composition. The total costs of growth were independent of ration and represented losses as heat of 23% of metabolizable energy surplus to the requirements for maintenance at energy equilibrium. Correction for the known costs of nonprotein deposition indicated a constant total cost of 1.43JJ⁻¹ protein deposited. Such constancy was reflected by rates of protein turnover that remained unchanged irrespective of ration and thus did not contribute to the costs of growth. Instead, heat losses of 17.65 J accompanied each milligram of protein turnover during maintenance alone, when requirements for turnover synthesis represented at least 20% of energy expenditure. This contribution, as well as a linear relation indicating an increase of 11.4J total heat loss mg⁻¹ protein synthesis, is shown to be remarkably consistent with previous data for mammals. We discuss evidence that associated costs of integrated processes may be the basis of these relations and suggest that whole-body turnover synthesis represents a general index of the energy requirements for maintenance.