EVIDENCE FOR AN ISOTOPIC STEADY STATE IN SOLUBLE COLLAGENS

The distribution of specific radioactivity was determined for soluble and insoluble collagens in guinea pigs multiply labeled with 3H-L-proline 6 weeks prior to sacrifice. Multiple extractions of neutral salt-soluble (0.15-0.30 M NaCl) and citrate-soluble collagens demonstrated constant but unequal specific activities which indicated the achievement of an isotopic steady state. The specific activity of acid-soluble collagens is 3-5 times higher than salt-soluble collagen and almost equal to that of insoluble collagen. The data indicate that there is a large difference in biological age between salt-soluble collagen and acid-soluble collagens. © 1969.