Isoelectric focusing of tyrosine hydroxylase

Abstract

Tyrosine hydroxylase (EC 1.14.16.2), catalyzes the conversion of L-tyrosine to 3,4-dihydroxyphenylalanine (L-DOPA), which is generally regarded as the rate limiting reaction in catecholamine synthesis. The activity of tyrosine hydroxylase (TH) is regulated by cAMP-dependent protein phosphorylation processes both in vitro (Weiner, et al., 1977; Ames, et al., 1978; Yamauchi and Fujisawa, 1979) and in situ (Harris, et al., 1974; Goldstein, et al., 1976; Patrick and Barchas, 1976; Weiner, et al., 1977; Waymire, et al., 1979). In addition, results from a variety of biochemical studies indicate that total TH activity may be determined by the relative catalytic activities of different molecular forms of the enzyme (Musacchio, et al., 1971; Kuczenski, 1973; Joh and Reis, 1975; Raese, et al., 1977; Weiner, et al., 1977; Nagatsu, et al., 1978). Furthermore, the relative proportions of the less active and more active forms of TH may determine the potential degree of TH activation which can be elicited during studies of stress. For example, Masserano and Weiner (1979) found that the adrenal supernatant of non-stressed rats contains two components of TH activity which exhibit distinct kinetic properties, a component with a high affinity for cofactor and a component with a lower affinity for cofactor.