Biotin carboxyl carrier protein in barley chloroplast membranes.

Biotin localized in barley chloroplast lamellae is covalently bound to a single protein with an approximate molecular weight of 21 000. It contains one mole of biotin per mole of protein and functions as a carboxyl carrier in the acetyl-CoA carboxylase reaction. The protein was obtained by solubilization of the lamellae in phenol/acetic acid/8 M urea. Feeding barley seedlings with [14C]-biotin revealed that the vitamin is not degraded into respiratory substrates by the plant, but is specifically incorporated into biotin carboxyl carrier protein.