Elsevier

Clinica Chimica Acta

Volume 46, Issue 2, 28 June 1973, Pages 153-160
Clinica Chimica Acta

A reassessment of the collagen reutilization theory by an isotope ratio method

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Abstract

The theory that intact collagen molecules (or large segments thereof) may be used in restructured collagen was tested by a double isotope-labelling technique. A 3H:14C isotope ratio was established in the mature connective tissue of ten female Wistar rats by an intraperitoneal injection of L-[3H]proline and [14C]glycine. Twentyeight days after the injection, granulation tissue was induced by subcutaneous dorsal implantation of ten hollow steel-mesh cylinders per animal. The cylinders were then removed along with skin samples at intervals over a 21-day period. During this time three animals received a diet supplemented with 15% unlabelled L-proline and three received a diet supplemented with 15% unlabelled glycine. If the granulation tissue consisted of reutilized collagen the isotope ratio would remain unchanged regardless of the diet. If the collagen came from de novo synthesis the isotope ratio would change because the 3H and 14C must pass through separate pools. Our results show that a large proportion of the radioactivity previously identified as arising from reutilized labelled collagen is actually the result of local protein catabolism and recycling of labelled amino acids for de novo synthesis. These experiments do not conclusively disprove the collagen reutilization theory but indicate the need for further investigations using a labelled compound that cannot be recycled.

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