Genetic Regulation of the Catecholamine Biosynthetic Enzymes

The pattern of inheritance of tyrosine hydroxylase (EC 1.14.3a), dopamine-/3-hydroxylase (1.14.2. l), and phenylethanolamine N-methyltransferase (EC 2.1. l), three enzymes in the catecholamine biosynthetic pathway, has been studied in two sublines of the Balb/c inbred mouse strain, Balb/cJ and Balb/cN. All three enzymes are nearly Z-fold greater in adrenals of the Balb/cJ line. Examination of the F1, Fz, and backcross progeny of the mating between these sublines reveals that single-gene loci control the steady state levels of each enzyme. The activity of all three enzymes is highly correlated in all of the hybrid generations studied. One explanation for these findings is that the loci are linked structural genes. An alternative hypothesis is. that a single regulatory gene locus controls the phenotypic expression of the three enzymes.