American Journal of Clinical Nutrition, Vol 25, 695-702, Copyright © 1972 by The American Society for Clinical Nutrition, Inc.

Leukocyte methylmalonyl-CoA mutase. I. Vitamin B₁₂ deficiency

¹ From the Department of Medicine, and the Central Hematology Laboratories, Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213

The leukocyte activity of the 5' deoxyadenosyl B₁₂-linked enzyme, methylmalonyl-CoA mutase, was measured in vitro in seven patients with vitamin B₁₂ deficiency (group I), six patients with anemia not due to vitamin B₁₂ lack (group II), and nine normal healthy adult controls (group III). Assay was based on the rate of utilization of enzymatically prepared, chromatographically purified ¹⁴C carboxy-labeled racemic methylmalonyl-CoA. The time course of the assay as described was linear over a 1-hr period at activities of 0.013 to 0.34 nmole/hr of methylmalonyl-CoA utilized.

Leukocyte mutase activities were measured without (basal) and with added dAB₁₂. Mutase activities were: group I basal, mean 0.034 (0.005 to 0.099); group II, mean 0.114 (0.017 to 0.309); group III, mean 0.286 ± 0.079 (0.170 to 0.459) nmole/mg leukocyte protein per hr. In the presence of added dAB₁₂ (100 to 500 ng) activities were: group I, 0.091 (0.018 to 0.190), group II, 0.093 (0.005 to 0.308), and group III, 0.232 ± 0.135 (0.090 to 0.510) nmole/mg leukocyte protein per hr. All seven vitamin B₁₂-deficient subjects showed enhanced leukocyte methylmalonyl-CoA mutase activity in the presence of added dAB_12. No correlation was apparent between leukocyte mutase ativities of the vitamin B₁₂-deficient subjects and the excretion of urinary methylmalonate, the severity of the anemia, or the presence of neurological impairment of the vitamin B₁₂-deficiency state.