Incorporation of [3H]proline into collagen and other proteins in rats fed diets with various zinc concentrations.

Incorporation of labeled proline into liver and skin proteins of weanling rats was studied during zinc restriction. Reduced incorporation of labeled proline into skin proteins including collagen hydroxyproline and an increase in its incorporation into liver and plasma proteins was observed with 0 or 0.046 mumol zinc/g diet, compared with 0.092, 0.153 or 0.306 mumol/g diet. Food (energy) restriction was then compared with zinc restriction, during recovery from protein restriction. A shift in proline incorporation from skin protein and skin collagen hydroxyproline, towards liver and plasma proteins, was closely correlated with body weight gain, whether it was limited by zinc restriction or by energy restriction. This diversion of label from skin to liver and plasma is probably mediated through mechanisms that limit growth during food restriction. Proline-incorporation patterns during zinc or energy restriction are clearly different from those of vitamin-C deficiency in guinea pigs.