Abstract
Proteostasis, the control of all aspects of assembly, turnover and removal of proteins within the cellular proteome by a proteostasis network of ∼2000 proteins present in all tissues, is achieved through both acute, nutritionally-sensitive, within tissue mechanisms, throughout the diurnal-cycle of feeding and fasting and through more long-term, between-tissue interactions, especially between long-bone length growth and muscle growth, both subject to adequate protein intakes. As part of proteostasis, protein turnover is mediated by several proteolytic systems especially lysosomal autophagy and the ubiquitin-proteasome system and is studied with various isotope tracer models which have revealed much about its extent and its physiological implications. Regulation of protein turnover operates at the levels of gene expression, ribosomal concentrations and translational activity and proteolysis, and is mediated mainly by amino-acids and insulin which together ensure efficient postprandial protein-utilization.