title: Kinetics of intracellular degradation of newly synthesized collagen.
abstract: The objective of this work was to determine the time dependence of the basal component of intracellular degradation of newly synthesized collagen. Chick embryo tendon fibroblasts were incubated with [14C]proline, and degradation was quantified by measuring hydroxy[14C]proline in a low molecular weight fraction. When cultures were pulse labeled for 15 min and then incubated under chase conditions for 105 min, the amount of degraded collagen attained a value equal to approximately 20% of the amount synthesized during the labeling period; the data were fit with a simple exponential function that had a 40-min rise time and a 12-min lag time. In continuously labeled cultures, the rates of collagen synthesis and secretion reached constant values within 15 and 45 min, respectively. Degradation products were first detected 6-9 min after collagen synthesis began and were transported out of the cells more rapidly than intact collagenous molecules; however, percent degradation increased slowly and did not reach a constant value even after 240 min of incubation. Since collagen degradation lags collagen synthesis, it follows that degradation is a posttranslational, rather than a cotranslational, process, and since degradation and secretion are kinetically distinguishable, it follows that they occur in parallel pathways. A simple nonlinear model for posttranslational processing of collagen is proposed.
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D002642:Chick Embryo; D003094:Collagen / Q000096:biosynthesis / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D007700:Kinetics; D011392:Proline / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D013710:Tendons / Q000378:metabolism*; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D014316:Tritium; D003094:Collagen; D011392:Proline