Biochemical characterization of biotin-responsive multiple carboxylase deficiency: Heterogeneity within the bio genetic complementation group

G. L. Feldman, Y. E. Hsia, B. Wolf

Research output: Contribution to journalArticle

15 Scopus citations

Abstract

Three biotin-dependent enzymes, pyruvate carboxylase (PC), propionyl CoA carboxylase (PCC), and β-methylcrotonyl CoA carboxylase (βMCC), were biochemically characterized in fibroblasts from two patients with neonatal multiple carboxylase deficiency. Genetic complementation analyses indicated that both cell lines, designated lines 1 and 2, were deficient in the various carboxylase activities and belonged to the bio complementation group. The activities of the three carboxylases became normal when line 2 cells were incubated in medium supplemented with biotin (1 mg/l) for 24 hrs, whereas 4-6 days were required to achieve maximum activities of PC, PCC, and βMCC (57%, 46%, and 29% of mean normal enzyme activity, respectively) in line 1 cells incubated in medium containing up to 10 mg/l biotin. Furthermore, PC activity in line 2 continued to increase under apparent gluconeogenic conditions in culture, but not in line 1. Thermostability studies suggested that biotin stabilizes PC and βMCC in both cell lines. PC in line 1 cells incubated with or without biotin was less stable than that in normal or line 2 cells, and the less than normal increase of enzyme activities in line 1, especially that of PC, may represent incomplete biotination. These results indicate that there is biochemical heterogeneity within the bio complementation group. Immunotitration with antibodies prepared against purified pig heart PCC demonstrated normal quantities of cross-reacting material in both lines and no differences in the amount of this material after incubation with supplemental biotin, despite the seven- to 20-fold increase in PCC activity. Thus, the increase in carboxylase activity in both bio lines appears to represent activation of pre-existing apocarboxylase rather than de novo enzyme synthesis. The primary defect in this form of multiple carboxylase deficiency may be in a common holocarboxylase synthetase or in biotin transport. If the defect is in the synthetase, the differences noted between the two bio lines could be explained by a difference in the enzyme's K(m) for biotin.

Original languageEnglish (US)
Pages (from-to)692-701
Number of pages10
JournalAmerican Journal of Human Genetics
Volume33
Issue number5
StatePublished - Jan 1 1981

ASJC Scopus subject areas

  • Genetics
  • Genetics(clinical)

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