Assignment of a locus required for flavoprotein-linked monooxygenase expression to human chromosome 2

Hybrid clones segregating human chromosomes were prepared by fusing mouse RAG cells to fresh human bone marrow cells and tested for the mixed-function oxygenase [flavoprotein-linked monooxygenase; RH, reduced-flavoprotein:oxygen oxidoreductase (RH-hydroxylating); EC 1.14.14.1] arylhydrocarbon hydrocarbon hydroxylase. Neither constitutive nor induced aryl hydrocarbon hydroxylase activity was detected in parental RAG cells. Induced aryl hydrocarbon hydroxylase was expressed in 4 out of 12 primary and 12 out of 19 secondary hybrid clones examined. Constitutive hydroxylase activity was detectable in 9 of the 15 inducible clones. All of the hybrid clones that exhibited constitutive hydroxylase activity were also inducible. There was a positive correlation between constitutive and induced hydroxylase activities although the absolute levels of the enzyme showed a wide range between different clones. Isozyme analysis performed on 12 primary and 19 secondary hybrid clones showed that aryl hydrocarbon hydroxylase activity was concordant with the expression of the human isozymes malate dehydrogenase (EC 1.1.1.37) and isocitrate dehydrogenase (EC 1.1.1.42), previously assigned to human chromosome 2. Isozyme markers for 19 other human chromosomes segregated independently from aryl hydrocarbon hydroxylase activity. The results suggest that the gene(s) required for aryl hydrocarbon hydroxylase activity are located on human chromosome 2.