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At least 19 recordsLinked to original sources
PubMed1975

Effects of sulfhydryl agents on the activation of tryptophan-5-monooxygenase from bovine pineal glands.

Partially purified tryptophan-5-monooxygenase (L-tryptophan, tetrahydropteridine: oxygen oxidoreductase (5-hydroxylating) EC 1.14.16.4)from bovine pineal gland was activated by preincubation with sulfhydryl agents such as dithiothreitol, L-cysteine, cysteamine, L-cysteine ethylester, N-acetyl-L-cysteine, 2-mercaptoethanol and reduced glutathione, at alkaline pH (optimum pH equals 8.5). Dithiothreitol was the most effective of these, leading to approximately 50-fold activation of the enzyme after preincubation. Fe-2+ or other reducing agents such as borohydride, dithionite and ascorbate facilitated the velocity of the activation in the presence of sulfhydryl agents. In the absence of sulfhydryl agents, no activation was observed even in the presence of Fe-2+ or other reducing agents, suggesting an obligatory role or sulhydryl agents during the activation. The relative velocity and full extent of the activation were dependent on the concentrations of both the sulfhydryl agent and the enzyme in the activation mixture. The kinetic analysis of the activation indicated that the sulfhydryl agent reacts with more than 2 sites in the enzyme; one type of site is reduced by sulfhydryl agents, Fe-2+ or other reducing agents and the other specifically modified by a sulfhydryl agent. The activated enzyme did not require any exogenous Fe-2+ for its catalytic activity, but some roles of iron maybe exist in its catalytic reaction. The optimum pH for catalytic reaction of the activated enzyme was approximately 6.5. The apparent Km for L-tryptophan and pteridine cofactor, tetrahydro-pteridine (2-amino-4-hydroxy-6,7-dimethyl-5,6,7,8-tetrahydropterin), of the activated enzyme were 30 and 35 muM respectively.

2,2'-Dipyridyl↗
PubMed1975

The thiol group of bovine serum albumin. High reactivity at acidic pH as measured by the reaction with 2,2'-dipyridyl disulphide.

The reaction between 2,2'-dipyridyl disulphide and the thiol group in bovine serum albumin has been studied at pH 1.1-7.9. At pH 5.5-7.9 the reaction rate was second order in dipyridyl disulphide and thiolate ion, as expected for an aliphatic thiol compound. Below pH 5.5 the reaction rate increased and became maximum at pH 2.6. The observed rate constant (110 M-1-s-1) was comparable with that at pH 6.6, although the thiolate ion concentration should be 10(4) times less at the lower pH. The increase in reactivity seemed to be correlated with the conformational change in serum albumin at pH 3.6-4.0. Increased nucleophilicity due to interaction with some suitable functional group might explain the high reactivity of the SH group at acidic pH.

2,2'-Dipyridyl↗
PubMed1976

Regulation of 6-hydroxy-2,4,5-triaminopyrimidine synthesis by riboflavin and iron in riboflavin-deficient mutants of Pichia guilliermondii yeast.

The effect of riboflavin and iron on 6-hydroxy-2,4,5-triaminopyrimidine synthesis rate was investigated in the cultures of the yeast Pichia guilliermondii (rib2 mutants) with the blocked second reaction to flavinogenesis. It was shown that riboflavin inhibited the 6-hydroxy-2,4,5-triaminopyrimidine synthesis rate in iron-rich and iron-deficient cells of mutants with low riboflavin requirements. Cycloheximide did not prevent the stimulation of 6-hydroxy-2,4,5-triaminopyrimidine synthesis caused by riboflavin starvation. 7-methyl-8-trifluoromethyl-10-(1'-D-ribityl)isoalloxazine strongly inhibited the 6-hydroxy-2,4,5-triaminopyrimidine synthesis, while 7-methyl-8-trifluoro-methyl-10-(beta-hydroxyethyl)izoalloxazine and galactoflavin exerted only a slight effect on this process. The 6-hydroxy-2,4,5-triaminopyrimidine synthesis rate in iron-deficient cells was significantly higher than in iron-rich cells. The 2,2'-dipyridyl treatment of iron-rich cells caused the stimulation of 6-hydroxy-2,4,5-triaminopyrimidine synthesis and cycloheximide abolished this effect. The results suggest that the activity of the first enzyme of flavinogenesis (guanylic cyclohydrolase) is under the control of feedback inhibition by flavins and the biosynthesis of this enzyme is regulated by iron.

2,2'-Dipyridyl↗
PubMed1977

Stimulation of the activity of prolyl hydroxylase in 3T3 fibroblasts by 1,10-phenanthroline.

In confluent cultures of 3T3 fibroblasts, incubated for 24 h with 1,10-phenanthroline at 10(-5)--10(-9) M, the activity of prolyl hydroxylase was significantly increased. 1,10-Phenanthroline was inhibitory at concentrations greater than 10(-4) M. The stimulatory effect of 1,10-phenanthroline manifests itself after 6 h incubation and increased with time up to 48 h. 2,2'-dipyridyl and 5,6-dimethyl-1,10-phenanthroline were also stimulatory; a nonchelating analog, 1,7-phenanthroline had no effect. Cycloheximide did not modify the 1,10-phenanthroline effect. The stimulatory effect does not seem to depend on the shift of an inactive precursor of prolyl hydroxylase to an active form because 1,10-phenanthroline was shown to be ineffective in logarithmically growing cells. While dialysis of washed and homogenized cells significantly increased prolyl hydroxylase activity in cell extracts, undialyzed 1,10-phenanthroline treated samples exhibited higher prolyl hydroxylase activity than dialyzed controls. These data suggested to us that 1,10-phenanthroline and other chelating agents may be forming complexes with certain metal ions or protein-metal ions which are inhibitory towards prolyl hydroxylase.

2,2'-Dipyridyl↗