The mechanism of inactivation of a single-stranded RNA phage, MS2, by AsA was investigated as a part of the studies on the mechanism of inactivation of viruses by AsA. Investigations on the effects of oxygen, oxidizing or reducing agents, metals or chelating agents, and free radical scavengers on the inactivation of the RNA phage by AsA indicated that the free radical intermediates formed during the course of oxidation of AsA are responsible for the inacti vation of the phage. Hydrogen peroxide and DAsA themselves had no effect on the infectivity of the phage. Sucrose density gradient centrifugation analyses indicated that the reactive radicals react with the phage RNA to cause strand scissions in the RNA.
The decrease of tyrosine hydroxylase activity in adrenal homogenate in scurvy was recovered after the administration of ascorbic acid. The causes of the increase in the enzyme activity after the administration of ascorbic acid have been studied. 1. No significant elevation in the enzyme activity was observed after the administration of reserpine to the scorbutic guinea pig. 2. A dose of metal chelating agent, α, α'-dipyridyl, prevented the ascorbic acid-induced or reserpine-induced increase in enzyme activity in the scorbutic and the non-scorbutic guinea pigs, respectively. 3. Tyrosine hydroxylase activity was partially recovered by the administration of FeSO4 to the scorbutic guinea pig. From these results, it became clear that the induction of tyrosine hydroxylase which was not observed in scurvy was due to the deficiency of Fe2+. These results suggested that ascorbic acid affected the induction of this enzyme via Fe2+.
Dihydrofolate synthetase (EC 6. 3. 2. 12) from Serratia indica IFO 3759 require a divalent cation and a univalent cation for its ac tivity. The divalent cation requirement was satisfied by magnesium ion, manganese ion or ferrous ion. High activity was obtained with 5 mM of magnesium ion. The effect of manganese ion was weak. The univalent cation requirement was satisfied by potassium ion, ammonium ion or rubidium ion, and high activity was obtained with 100 mM of each univalent cation. Increase in the potassium concentration lowered Km values for dihydropteroate and L-glutamate, and raised Vmax for ATP and dihydropteroate. Potassium ion had little effect on Km value for ATP. These results suggest that potassium ion may function on the affinities of dihydropteroate and L-glutamate to the enzyme. Dihydrofolate synthetase was inhibited by the addition of reduced forms of homopteroic acid. Stronger inhibition was observed by dihydrohomopteroate than by tetrahydrohomopteroate.
The contents of B6 vitamers were measured in the brains of mice treated with DL- and D-PeA, When a single convulsant dose of DL-PeA was injected, PLP content was decreased, being accompanied with production of PLP-thiazolidine. The effect of DL-PeA on PLP content was evident far before the occurrence of the convulsions. The administration of PN together with DL-PeA prevented the onset of seizures and lessened the effect of DL-PeA on PLP content. The same amount of D-PeA did not invoke seizures, but caused a small but significant decrease in PLP content
This study was concerned with the detailed identification of the second product involved in the riboflavin synthetase reaction with riboflavin synthetase from Eremothecium ashbyii and a trapping agent, glyoxal. Thus, a green fluorescent compound accumulated during the incubation. The compound was purified through various column chromatography steps, and was examined by UV, IR, excitation and emission spectra and paper chromatography to prove that the isolated compound was 8-ribityllumazine. Accordingly it was concluded that a second product in riboflavin synthetase reaction was 4-ribitylamino-5amino-2, 6-dihydroxypyrimidine, the fragment, except for C-6 and C-7 of 8-ribityllumazine, being an incorporated glyoxal portion.
1. The tyrosinase reaction in the presence of a thiol compound was studied using mushroom tyrosinase (EC 1. 10. 3. 1) with regard to catechol-thiol conjugates. 2. Although tyrosine hydroxylation of tyrosinase was extremely decreased in the presence of a thiol compound, the inhibitory effect was removed by the addition of a pyrocatechol-cysteine conjugate, S-(2, 3-dihydroxyphenyl) cysteine, which was not oxidized by the enzyme. 3. The pyrocatechol-cysteine conjugate was also able to shorten the lag period of tyrosinase-dependent tyrosine hydroxylation. 4. The sigmoidal reaction curve of tyrosine hydroxylation observed in the presence of sulf hydryl compounds was found to be caused by the catechol-thiol conjugates, the final products of the enzyme reaction, which counteract the inhibitory effect of sulf hydryl compounds. 5. The pyrocatechol-cysteine conjugate, on the other hand, was shown to cause the decrease of the reaction rate of the enzyme during incubation.
The object of this study was to determine the effects of individual amino acid supplements on the development of tyrosine toxicity in growing rats fed 10% casein containing 5% tyrosine. Each amino acid was added at levels equivalent to its content in 20% casein. Supplement of methionine to the high tyrosine diet partially alleviated both growth depression and pathological lesions. Threonine and cystine had a somewhat beneficial effect, but the single addition of other amino acids was not effective. Besides, some amino acids enhanced the severity of the toxicity even more. The effects of methionine supplementation were highest at 0.66 to 1.32 levels (equivalent to the methionine content in 20 to 40% casein). By the supplement of both 0.66 % methionine and 0.90% threonine to the high tyrosine diet, growth was significantly improved and toxic lesions were completely prevented. It was confirmed that the counteracting effects to the toxicity, caused by the extra addition of protein (casein) to rats fed a high tyrosine-low protein diet, were mainly attributed to the effectiveness of the methionine and threonine, i.e., first-and second-limiting amino acids, respectively, contained in it.