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).