The vitamin B12-deficient rat as a possible model of ketotic hyperglycinemia

The rate of oxidation to respiratory CO2 of both carbon 1 of propionate and carbon 1 of glycine was decreased significantly in vitamin B12-deficient rats, to 50% and 82% of the control rate, respectively. The activity of the glycine synthase system was reduced during vitamin B12 deficiency to 25% of control activity. Serine hydroxymethyltransferase activity was similar for vitamin B12-deficient and control rats. Plasma glycine concentration in vitamin B12-deficient rats (253 +/- 16 nmol/ml) did not differ significantly from that of control rats (226 +/- 12 nmol/ml). Propionate oxidation was significantly impaired in biotin-deficient rats. However, this impairment, to 66% of the control rate, was not as large as that generated by vitamin B12 deficiency. In contrast to the result obtained in vitamin B12-deficient animals, no significant decrease in glycine oxidation could be demonstrated in biotin-deficient animals. Plasma glycine concentration of fasted biotin-deficient rats (339 +/- 26 nmol/ml) did not differ significantly from that of their controls (371 +/- 32 nmol/ml).