Metabolism of the Vitamin-A-Transporting Protein Complex: Turnover of Retinol-Binding Protein, Prealbumin and Vitamin A in a Primate (Macaca Irus)

The kinetics of the specific retinol transport system in plasma, including the retinol-binding protein (RBP) and prealbumin, have been investigated in the Cynomolgus monkey (Macaca irus) with iodine-labelled and endogenously 35S-labelled proteins as tracers. The biological half-times were 1.9 hours for RBP in free form. 6.6 hours for RBP interacting with prealbumin, and 22.5 hours for prealbumin itself. The results indicate that RBP is degraded mainly when in free form. The turnover of labelled retinol attached to RBP was compatible with a certain reutilization of the vitamin as contrasted to RBP.