Metabolism of rabbit skin collagen. Differences in the apparent turnover rates of type-I- and type-III-collagen precursors determined by constant intravenous infusion of labelled amino acids

Abstract

Growing rabbits were infused for up to 10 h with labeled proline, tyrosine and leucine to achieve plateau conditions within body free pools: for [3H]proline infusion, blood free-proline specific radioactivity remained constant after about 1 h. For individual animals, type-I and type-III-collagen precursors were isolated by precipitation with (NH4)2SO4 and DEAE-cellulose chromatography. Infusion of 3H- and 14C-labeled proline and tyrosine concurrently for different periods of time showed that type I procollagen reached plateau specific radioactivity within 3 h and 90% of the plateau value after 2 h, corresponding to a calculated apparent t1/2 [half time] of less than 26 min. For Type I procollagen plateau values were taken as precursor amino acid pool specific radioactivities. The type-III-collagen-precursor fractions consistently showed lower rates of label incorporation and, assuming type I and type III collagens are synthesized from the same amino acid pools, kinetic analysis revealed an apparent t1/2 for the isolated type-III-collagen precursors of 3.9 h. For proline, there were large variations between animals in the ratio between the collagen synthesis precursor pool collagen synthesis and the skin homogenate free pool (0.31 .+-. 0.13, mean .+-. SD), so that collagen synthesis rates based solely on total tissue free-pool values for proline are subject to large and inconsistent errors.