Nagatsu Toshiharu

Inhibition of dopamine β-hydroxylase by fusaric acid (5-butylpicolinic acid) in vitro and in vivo

Abstract Fusaric acid (5-butylpicolinic acid) was found to be a potent inhibitor of dopamine β-hydroxylase in vitro and in vivo . Fusaric acid inhibited the enzyme by 50 per cent at a concentration of 3 × 10 −8 M. Kinetic studies with purified dopamine β-hydroxylase showed that the inhibition by fusaric acid was of the uncompetitive type with the substrate and of the mixed type with a cofactor, ascorbic acid. Fusaric acid lowered endogenous levels of norepinephrine and epinephrine in brain, heart, spleen and adrenal glands. Maximum depletion of norepinephrine and epinephrine was observed between 3 and 6 hr after the administration of fusaric acid. Since dopamine β-hydroxylase activity in adrenal medulla was found to be inhibited in vivo after the administration of fusaric acid, the decrease in the catecholamine levels is attributed to the inhibition of norepinephrine synthesis at the dopamine β-hydroxylase stage.

Pteridines as cofactor or inhibitor of tyrosine hydroxylase

Abstract The relationship between the structure and the cofactor or inhibitor activity of various synthetic 5, 6, 7, 8-tetrahydropteridines (including tetrahydrobiopterin, the possible natural cofactor) on bovine adrenal tyrosine hydroxylase, has been studied. 5,8-Unsubstituted tetrahydropterins (2-amino-4-hydroxy-5, 6, 7, 8-tetrahydropteridines) had the cofactor activity, among which tetrahydrobiopterin had the lowest Km value and the highest Vmax value. Norepinephrine inhibited tyrosine hydroxylase in competition with tetrahydrobiopterin or other tetrahydropterin cofactors. 8-Unsubstituted 2-amino-4-hydroxytetrahydropteridines with an alkyl group and the N—5 position inhibited the activity of the enzyme in competition with 6, 7-dimethyltetrahydropterin, their 2-hydroxy analogues did not inhibit the enzyme. Substitution of the tetrahydropterins at the N—8 position by an alkyl group abolished their inhibitor activities. 5-Methyl-6, 7-diphenyltetrahydropterin was the most potent inhibitor. The possibility that the cofactor or inhibitor activities which have been measured are not due to the tetrahydropteridines but due to the corresponding dihydropteridines is ruled out from the facts that 7, 8-dihydropterins had no cofactor activity and that the 5-alkyltetrahydropterins were stable during the incubation in the assay system including mercaptoethanol. However, 7,8-dihydropterins inhibited the activity in competition with 6, 7-dimethyltetrahydropterin as a cofactor.

Comparative studies on the structure of human tyrosine hydroxylase with those of the enzyme of various mammals.

Abstract 1. Tyrosine hydroxylase (TH) is the first and rate-limiting enzyme in catecholamine biosynthesis. 2. The structures of TH from various species have been elucidated. 3. We have cloned and determined the sequences of four types of human TH cDNA and human TH genomic DNA. 4. We have compared the amino acid sequences of TH from various species. 5. The results indicate that the amino acid sequences of TH are highly conserved among various species, and that TH consists of the regulatory domain containing serine residues which are phosphorylated by protein kinases and of the catalytic domain where the substrates, tyrosine and oxygen, and the cofactor, tetrahydrobiopterin, are bound. 6. Comparison of amino acid sequences among TH from various species can give us useful information on the functional importance of each amino acid residue.

Effects of heterocyclic amines in food on dopamine metabolism in nigro-striatal dopaminergic neurons

Abstract We investigated the effects of 14 heterocyclic amines in food on nigro-striatal dopaminergic neurons. Among 14 compounds tested, 3-amino-1,4-dimethyl-5 H -pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) caused substantial decreases in 3,4-dihydroxy-phenylalanine (DOPA) formation in striatal tissue slice system. When Trp-P-1 or Trp-P-2 was unilaterally infused in the rat striatum by an In vivo micro-dialysis technique, both compounds produced a transient increase of dopamine (DA) and continuous decreases in the metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic add (DOPAC) in the perfusate. This suggests that the two compounds inhibit monoanune oxidase (MAO) in vivo . Indeed they were found to be very potent inhibitors of MAO in vitro . Systemic administration of Trp-P-1 to C57 Black mice caused a marked decrease of DOPAC content and a significant increase of DA in the striatum, indicating inhibition of MAO In vivo . These results suggest that Trp-P-1 and Trp-P-2 contained in food could alter the metabolism of DA in the brain.

Lysyl oxidase activity in human normal skins and postburn scars

Abstract Lysyl oxidase activity of human normal skins derived from the frontal thighs of 33 subjects showed large variations and the mean value was 11 4 55 ± 7 172 (S.D.) cpm/g of wet weight tissue. The age of lesion affected the lysyl oxidase activity in postburn scars. Granulation tissues showed a fairly low activity; however, the activity increased sharply within 2–3 months, and reached a significantly higher value than that of normal skin. The high level of activity continued for up to 2–3 years, then gradually decreased to normal range after 5 years or so. Lysyl oxidase activity was detected only after 4 M urea treatment of tissues. Benzylamine oxidase activity also showed large variations in both normal skins and postburn scars, with mean values of: 0.128 ± 0.077 (S.D.) and 0.145 ± 0.090 (S.D.) mmol/g of wet weight/h, respectively. No correlation was observed between lysyl oxidase and benzylamine oxidase activities. The granulation tissue showed significantly high values of benzylamine oxidase activity in contrast to the low values of lysyi oxidase activity.

Monoamine oxidase activity of the thyroid glands in thyroid disease

Abstract Monoamine oxidase activities of the thyroid glands obtained at thyroidectomy from 29 patients with goiter were measured using serotonin and kynuramine as substrates. Significant elevation of monoamine oxidase activity of the thyroid gland was observed in the case of malignant goiter.