Hydroxylation of proline after the release of proline-rich polypeptides from ribosomal complexes during uninhibited collagen biosynthesis

Collagen synthesis and secretion by isolated rat renal glomeruli

Glomeruli were isolated from rat renal cortex and incubated with radioactive lysine to study in vitro collagen synthesis in these preparations. Glomerular basement membrane was obtained by sonication, and the appearance of [-14C]lysine and hydroxylysine in medium, membrane and intracellular proteins was determined. Total glomerular incorporation of [-14C]lysine into protein linearly increased for up to 2-h period, and membrane hydroxylysine content gradually rose during this time. Hydroxy[-14C]lysine was recovered in the 105 000 times g pellet, reaching a hydroxylysine content of 22 percent in this intracellular fraction after 90 min of incubation. 60 percent of the protein secreted into the medium, and about 75 percent of newly synthesized sonicated basement membrane was acetic acid soluble. Hydroxylysine content was 33 percent in the acetic acid-insoluble fraction of sonicated membrane, suggesting that basement-membrane collagen was a significant component of total collagen synthesized by these preparation, The ability of isolated glomeruli to synthesize and secrete basement-membrane protein will be useful for studies concerning control of glomerular collagen and basement-membrane synthesis.

Influence of ascorbic acid on ribosomal patterns and collagen biosynthesis in healing wounds of scorbutic guinea pigs

Scorbutic guinea pigs were wounded and the influence of administering ascorbic acid 6 days later was studied with respect to cellular morphology, ribosomal distribution and protein synthesis. Electron-microscopic studies revealed that the dilated endoplasmic reticulum observed in the fibroblasts of scorbutic wound tissue had reverted to a normal configuration 24h after intraperitoneal injection of 100mg of ascorbate. Quantitative determination of the distribution of free and membrane-bound ribosomes indicated a significant increase in membrane-bound ribosomes in wound tissue from ascorbate-supplemented (recovery) animals. Sucrose-density-gradient centrifugation indicated a significant increase in the proportion of large membrane-bound polyribosomes in the range 300-350S and a concomitant decrease in 80S monoribosomes in the ribosome sedimentation profile of recovery tissue. Determination of the synthesis of non-diffusible [(3)H]hydroxyproline in scorbutic and recovery wounds showed a 3-4-fold stimulation in peptidyl-proline hydroxylation in recovery tissues. Studies carried out in which scorbutic and recovery tissues were incubated with [(14)C]leucine indicated that general protein synthesis, as measured by (14)C incorporated into non-diffusible material/mug of DNA, was unaltered by ascorbate supplementation. Similar studies of [(3)H]proline incorporation suggested that in recovery tissues there was a small but significant increase in [(3)H]proline incorporated/mug of DNA, which probably represents an increase in protocollagen synthesis. This observation correlates well with the increase seen in recovery tissues of large polyribosomes on which collagen precursor polypeptides are known to be synthesized. Preliminary characterization of the repair collagen synthesized by recovery animals showed it to be a typical Type I collagen having the chain composition (alpha(1))(2)alpha(2). The extent of glycosylation of the hydroxylysine of the newly synthesized collagen was greater than that reported for either normal guinea-pig dermal collagen or dermal scar collagen.