Heterogeneity of holocarboxylase synthetase in patients with biotin-responsive multiple carboxylase deficiency

Holocarboxylase synthetase activity has been determined in fibroblasts of 7 patients with the neonatal form of biotin-responsive multiple carboxylase deficiency. The normal K(m) for biotin was 15 ± 3 nmol/l, while in the patients the values ranged from 48 to 1,062 nmol/l. The mean maximum velocity was 27% of normal. Differences among the values obtained for the K(m) for biotin and the heat stability of holocarboxylase synthetase suggested that the patients studied represented at least 4 distinct variants at the holocarboxylase synthetase locus.