Investigations on collagen proline hydroxylation in a cell-free system

A convenient method for the identification and estimation of soluble elastin synthesis in vitro

A method is described by which newly synthesized soluble elastin can be routinely and conveniently identified and estimated in vitro without the need for unlabelled carrier tropoelastin. Aortic tissue from 11 day old chick embryos is incubated in the presence of [14C] L-proline and [3H] L-valine and the distributions of [14C] proline-, [14C] hydroxyproline-and [3H] valine-labelled proteins on SDS-polyacrylamide gels are determined. Soluble elastin is identified as a [14C] hydroxyproline-labelled peak of molecular weight approximately 70,000 daltons which also incorporates large quantities of [3H] valine and has a [14C] hydroxyproline/[14C] proline ratio of about 0.2. Whereas the hydroxyproline label can be used to estimate newly synthesized soluble elastin even after several hours of incubation, similar use of the [3H] valine label is limited to short incubation times. Paradoxically, the quantity of [14C] hydroxyproline-labelled soluble elastin detected by the assay decreases with increased incubation time. This fall-off in labelled soluble elastin is not due to an increase in the rate of crosslinking of the protein over the course of the incubation. Soluble elastin is detectable both in tissue extract and medium fractions. The presence of hydroxyproline-labelled protein fragments in the medium fraction is evidence of proteolytic breakdown of collagen or elastin or both proteins. This proteolytic activity is augmented by the inclusion of serum in the incubation medium and is not inhibited by phenylmethylsulfonylfluoride. The method provides a convenient assay by which factors affecting the synthesis and secretion of soluble elastin may be studied.

Collagen biosynthesis in normal human skin, normal and hypertrophic scar and keloid

A comparison of the rates of synthesis of collagen in normal skin, normal and hypertrophic scars, and keloids has been made by measuring the rate of incorporation of [14-C]-proline into peptide-bound [14-C]-hydroxyproline by tissue minces in vitro. The rate of synthesis of collagen, as measured by this technique, was significantly higher in skin than in normal scars whether the incorporation of radioactivity into hydroxyproline were expressed in terms of wet weight of tissue, weight of tissue DNA or weight of tissue hydroxyproline. The abnormal scar types exhibited similar rates of collagen synthesis, which were significantly higher than the rate in normal scars. Although the rates in both abnormal scar types appeared to be similar to that in normal skin when expressed in terms of wet weight of tissue, and weight of tissue hydroxyproline, they were seen to be lower than in skin in terms of weight of tissue DNA. The rate of synthesis of proteins generally, as measured by total radioactivity in non-diffusible peptides, was highest in normal skin and hypertrophic scar and lowest in keloid. The ratio of radioactivity in non-diffusible hydroxyproline to total non-diffusible radioactivity was almost twice as high in keloid as in normal scar, with intermediate values being observed in hypertrophic scar and normal skin. This indicated that collagen accounted for a higher proportion of the proteins being synthesised in keloid than in normal scar. The results confirm previous conclusions, from determination of the activity of the enzyme collagen proline hydroxylase, that the excessive accumulation of collagen in hypertrophic scars and keloids may, at least in part, be due to abnormally high rates of collagen synthesis in comparison to normal scars.

Salicylate-induced inhibition of collagen and mucopolysaccharide biosynthesis by a chick embryo cell-free system

The ability of a chick embryo cell-free system to synthesize collagen, mucopolysaccharide and non-collagen protein in the presence of sodium salicylate was studied. Added creatine phosphate together with endogenous creatine kinase was the ATP generating system. The incorporation of labelled proline or labelled glucose into collagen or mucopolysaccharide respectively depended on ATP level in the cell-free system used. Salicylate inhibited collagen and mucopolysaccharide synthesis to a greater extent than non-collagen protein synthesis. The ability of the cell-free system to hydroxylate labelled protocollagen was inhibited 50% by storage at −18°. Ferrous iron reversed this inhibition. Salicylate prevented the restoration of the enzyme activity by ferrous iron. Incorporation of radioactivity into hyaluronic acid, when labelled UDP-glucuronic acid and UDP-N-acetylglucosamine were supplied, was inhibited 17% by salicylate. Under the same conditions 47% inhibition of incorporation into chondroitin sulphate was seen. This suggests that UDP-N-acetyl-glucosamine-UDP-N-acetylgalactosamine epimerase is inhibited by salicylate.

Protocollagen proline hydroxylase of the mouse uterus during pregnancy and post-partum involution

1. The protocollagen proline hydroxylase in mouse uterus was found to be similar to that in other animal sources in its subcellular distribution and cofactor requirements. 2. The activities of this enzyme in uterine tissue from non-pregnant mice were comparable with those in various embryonic tissues. 3. In the second half of pregnancy the protocollagen proline hydroxylase activity increased markedly. 4. After parturition the activity of this enzyme decreased rapidly, reaching normal non-pregnant values at 24h post partum. The results suggest a good correlation between the synthesis of collagen and the activity of protocollagen proline hydroxylase.