Oxidation Of Histidine Research Articles

4752573 Use of tetrahydrobiopterin to enhance the proliferative activity of interleukin-2 on T cells

Aromatic pterins accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder, due to the oxidation of tetrahydrobiopterin, the biologically active form of pterins. In this work, we have investigated the ability of pterin, the parent compound of aromatic pterins, to photosensitize the oxidation of histidine in aqueous solutions under UV-A irradiation. Histidine is an α-amino acid with an imidazole functional group, and is frequently present at the active sites of enzymes. The results highlight the role of the pH in controlling the competition between energy and electron transfer mechanisms. It has been previously demonstrated that pterins participate as sensitizers in photosensitized oxidations, both by type I (electron-transfer) and type II mechanisms (singlet oxygen (1O2)). By combining different analytical techniques, we could establish that a type I photooxidation was the prevailing mechanism at acidic pH, although a type II mechanism is also present, but it is more important in alkaline solutions.

Effect of thiouracil in modifying folate function in severe vitamin B 12 deficiency

The effects of thiouracil in correcting defects in folic acid function produced by B 12 deficiency were studied. Addition of the thyroid inhibitor, thiouracil, to a low methionine diet containing B 12, increased the oxidation of [2- 14C]histidine to carbon dioxide, and increased liver folate levels. Addition of 10% pectin to the diet accentuated B 12 deficiency as evidenced by a greatly decreased rate of histidine oxidation (0.19%) and an increased excretion of methylmalonic acid. Addition of thiouracil to the diet restored folate function as measured by increased histidine oxidation and increased liver folate levels similar to that produced by addition of methionine to a B 12-deficient diet. Thiouracil decreased methylmalonate excretion, and increased hepatic levels of B 12 in animals on both B 12-deficient and -supplemented diets. Hepatic methionine synthase was increased by thiouracil, which may be the result of the elevated B 12 levels. S-Adenosylmethionine and the enzyme methionine adenosyltransferase were also increased by thiouracil. Thus it is possible that the effect of thiouracil in increasing folate function consists both in the effect of thiouracil in decreasing levels of methylenetetrahydrofolate reductase, and also in its action in increasing S-adenosylmethionine which exerts a feedback inhibition of this enzyme.

Effect of high levels of dietary folic acid on folate metabolism in vitamin B12 deficiency.

The effect of administering high levels of folic acid to vitamin B12-deficient animals was studied. In B12 deficiency histidine oxidation is decreased. This is the result of both decreased liver folate levels and increases in the proportion of methyltetrahydrofolates. The purpose of this study was to determine if the addition of very high levels of folic acid to B12-deficient diets could increase liver folates and thereby restore histidine oxidation. Rats were fed a soy protein B12-deficient diet containing 10% pectin which has been shown previously to accelerate B12 depletion. When this diet was supplemented with B12 and folic acid, histidine oxidation was 5.4% in 2 h and the livers contained 3.49 micrograms of folate/g. In the absence of B12, the histidine oxidation rate was 0.34% and the liver folate level was 1.33 micrograms/g. When 200 mg/kg of folic acid was added to the B12-deficient diet there was no increase in histidine oxidation (0.35%) but the liver folates were increased to 3.68 micrograms which is about the same as that with B12 supplementation. The percentage tetrahydrofolate of the total liver folates was the same with and without a high level of dietary folic acid. Thus there was an increase in the absolute level of tetrahydrofolate without any increase in folate function as measured by histidine oxidation. Red cell folate levels were the same with and without B12, which is in contrast to the markedly lower liver folate levels in B12 deficiency. These data suggest a difference between B12 regulation of folate metabolism in the liver and in the bone marrow.

Experiments on the biological activities of various fractions of the folic acid antagonist “X-methyl” folic acid

A crude synthetic preparation called crude “X-methyl” folate has previously been shown to function as a folate antagonist for rats and chicks. This product has been shown to contain two folate antagonists: (1) 9-methyl folate, present as 6% by weight of the product and which has low activity as a folate antagonist for Streptococus faecalis, and (2) pyrrofolic acid, a compound present in small amounts (0.04%), but having high anti-folate biological activity for S. faecalis. These experiments deal with the antifolate activity of these two fractions for the rat as measured by their effects on histidine oxidation. Rats were fed a purified diet based on 20% vitamin-free casein and containing 1.0% sulfasuxidine. When this diet was supplemented with a marginal amount of folic acid (0.3 mg per kg diet), the addition of 4 g of crude antagonist decreased histidine oxidation and decreased liver folate levels. The addition of 240 mg of pure 9-methyl folic acid (amount of 9-methyl folic acid in 4 g of crude) produced similar decreases in histidine oxidation and liver folate levels. A concentrate of pyrrofolic acid (equivalent to 4 g of crude) free of 9-methyl folic acid produced no decrease in histidine oxidation and minimal changes in liver folate. This indicates that the folate antagonist activity observed previously with animals is probably due to the 9-methyl folic acid component rather than to the pyrrofolic acid activity.

Modification of hepatic folate metabolism in rats fed excess retinol

Feeding rats a diet containing 1000 IU of retinol/g diet enhances the folate-dependent oxidation to CO 2 of formate and histidine. The activity of hepatic methylenetetrahydrofolate reductase, which plays a critical role in the regulation of liver folate metabolism, is suppressed in these animals, resulting in decreased 5-methyltetrahydrofolate synthesis. This ensures a greater concentration of hepatic tetrahydrofolate, the coenzyme on which formate and histidine oxidation depend, but also compromises the level of S-adenosylmethionine in the liver.

4‐THIOURIDINE AS A PHOTODYNAMIC AGENT

Abstract— The 4‐thiouridine photosensitized oxidation of tryptophan and histidine has been followed by measuring the oxygen consumption. The yield of photooxidation has been compared using 4‐thiouridine and hematoporphyrin as photosensitizers.

Autooscillating chemiluminescence in the oxidation of histidine with bromate

Autooscillating chemiluminescence in the oxidation of histidine with bromate

Determination of amino acid requirements of young pigs using an indicator amino acid.

Mixtures of skim milk and free amino acids were compared as diets for pigs which would allow manipulation of dietary amino acid levels. Piglets gained 208 g/d between 3 and 14 d of age on the skim-milk diet, but replacement of 600 g/kg of the dietary nitrogen with free amino acids reduced growth rate to 148 g/d. Supplementation of a lysine-deficient diet with lysine reduced the catabolism of [14C]phenylalanine showing that phenylalanine catabolism could be used as an indicator of the adequacy of diet with respect to another essential amino acid. The dietary level of phenylalanine which would provide an excess for catabolism by the piglet was estimated directly by measuring the influence of dietary phenylalanine level on [14C]phenylalanine oxidation. Reduction of the dietary phenylalanine level below 7 g/kg had no effect on phenylalanine oxidation, whereas increasing the dietary phenylalanine level above 7 g/kg resulted in a linear increase in phenylalanine oxidation. An indirect estimate of histidine requirement was made by examining the influence of dietary histidine level on [14C]phenylalanine oxidation. In diets containing more than 4 g histidine/kg, phenylalanine oxidation was minimal. In diets containing less than 4 g histidine/kg, [14C]phenylalanine oxidation increased as the level of dietary histidine was reduced. This showed that the utilization of the essential amino acid phenylalanine, for protein synthesis, was not limited by histidine supply in diets containing more than 4 g histidine/kg. A direct estimate of histidine requirement was made by examining the influence of dietary histidine level on [14C]histidine oxidation. Diets with more than 4 g histidine/kg contained an excess which was catabolized: there was a linear increase in histidine oxidation in response to dietary histidine levels greater than 4 g/kg. This confirmed the previous indirect estimate of histidine requirement.

Photosensitization by methotrexate photoproducts.

Abstract— Photoproducts induced upon excitation of methotrexate by UV light have been separated by ion exchange chromatography. They include 2,4‐diamino‐6‐pteridinecarboxylic acid, 2,4‐diamino‐6‐pteridine‐carboxaldehyde and other unidentified pteridine derivatives. The same photoproducts can be also formed upon photodynamic reaction using hematoporphyrin as photosensitizer. In oxygen saturated aqueous solutions (pH∼7), methotrexate photoproducts sensitize the oxidation of histidine and tryptophan by UV light by a process involving singlet oxygen. In aqueous solutions containing albumin or in human serum, the same photoproducts are formed from free methotrexate but not from albumin‐bound methotrexate. In the latter case the results may suggest that methotrexate covalently binds to albumin upon excitation with UV light either in absence or in presence of oxygen. These results could explain the photosensitization accompanying cancer chemotherapy with high dose methotrexate and also the synergistic effects of PUVA + low dose methotrexate in psoriasis therapy.

Kinetic and mechanistic studies of oxidation of arginine, histidine, and threonine in alkaline medium by N‐chloro‐N‐sodio‐p‐toluenesulfonamide

AbstractThe kinetics of oxidation of arginine, histidine, and threonine by chloramine‐T (CAT) have been investigated in alkaline medium at 35°C. The rates are first order in both [CAT] and [amino acid] and inverse fractional order in [OH−] for arginine and histidine. The rate is independent of [OH−] for threonine. Variation of ionic strength and addition of the reaction product, p‐toluenesulfonamide, or Cl− ions had no effect on the rate. A decrease of the dielectric constant of the medium by adding methanol decreased the rate with arginine, while the rates increased with histidine and threonine. The solvent isotope effect was studied using D2O. (kobs)/(kobs) was found to be 0.55 and 0.79 for arginine and histidine, respectively. The reactions were studied at different temperatures, and activation parameters have been computed. The oxidation process in alkaline medium, under conditions employed in the present investigations, has been shown to proceed via two paths, one involving the interaction of RNHCl (formed rapidly from RNCl−), with the amino acid in a slow step to form monochloroamino acid, which subsequently interacts with another molecule of RNHCl in a fast step to give the products, p‐toluenesulfonamide (RNH2), and the corresponding nitrile of the amino acid (R'CN). The other path involves the interaction of RNCl− with the amino acid in a similar way to give RNH2 and R'CN. Mechanisms proposed and the derived rate laws are consistent with the observed kinetics. The rate constants predicted using the derived rate laws, as [OH−] varies, are in excellent agreement with the observed rate constants, thus justifying these rate laws and hence the proposed mechanistic schemes.

Reactions of singlet oxygen in humic waters

SUMMARY. The oxidation of 2, 5‐diniethylfuran (DMF) to cis‐1, 2‐ diacetylethylene (DAE) is a specific test for singlet oxygen (1O2). A method has been developed for the measurement of DAB by direct injection gas chromatography. By the use of this method, the photochemical generation of 1O2 has been demonstrated in samples of two Canadian humic waters.Two other photochemical reactions probably mediated by 1O2generation, the oxidation of histidine and the inactivation of a‐chymotrypsin, have been demonstrated in these waters.The possible ecological and environmental implications of these findings are discussed.

Free radical reactions with proteins and enzymes: The inactivation of bovine carbonic anhydrase B

A comparison of the inactivation of bovine carbonic anhydrase B (carbonate hydro-lyase, EC 4.2.1.1) by .OH, (SCN) 2 • and Br 2 • shows that the enzyme contains one or more essential tryptophan residues. Direct oxidation of histidine and tyrosine residues by the radicals is less important in causing inactivation of the enzyme. The effectiveness of all these radicals in inactivating carbonic anhydrase decreases with increasing pH in the region where the activity-linked ionizable group dissociates. Differences between the rates of reaction of Br 2 • and (SCN) 2 • with the holo- and apo-enzyme and between the resulting transient product spectra indicate that access to the reactive tyrosine and tryptophan residues is diminished by the presence of Zn 2+ in the active site region.

The role of methionine in regulating folate-dependent reactions in isolated rat hepatocytes

In isolated rat hepatocytes, histidine and formate, are oxidized to CO 2 by folate-dependent reactions. These reactions are stimulated two- to fourfold by the addition of l-methionine, dl-homocysteine, S-adenosyl- l-methionine (Ado-Met), or S-adenosyl- l-homocysteine (Ado-Hcy). These compounds all increase the hepatocyte concentration of Ado-Met and Ado-Hcy. Substrates of hepatic catechol O-methyltransferase, such as l-Dopa methyl ester and 3,4-dihydroxyphenylacetic acid, decrease the hepatocyte concentration of Ado-Met in the presence or absence of added l-methionine or dl-homocysteine. The catechols do not affect the concentration of Ado-Hcy, but they inhibit the oxidation of formate and histidine. Thus, there is an excellent positive correlation between the rate of histidine and formate oxidation and the concentration of Ado-Met. There is no correlation between the rate of these reactions and either the Ado-Hcy concentration or the concentration ratio of Ado-Met:Ado-Hcy. Ado-Met inhibition of rat hepatic 5,10-methylene tetrahydrofolate reductase activity is reversed by Ado-Hcy, but the dependency of rat hepatic 5-methyltetrahydrofolate-homocysteine transmethylase activity (methionine synthetase) on Ado-Met is not altered by Ado-Hcy. These results indicate that methionine, through its conversion to Ado-Met, regulates folate-dependent reactions in isolated hepatocytes by increasing activity of methionine synthetase which leads to an increased concentration of tetrahydrofolate. That methionine and Ado-Met increase the hepatocyte concentration of nonmethyltetrahydrofolate compounds and decrease the hepatocyte concentration of 5-methyltetrahydrofolate supports this hypothesis.

Factors influencing the photosensitizing properties and photoluminescence of thioflavin T

The fluorescence intensity of aqueous solutions of thioflavin T greatly increases when the dye is bound to ribonucleic acid and to single-stranded poly-nucleotides containing purine bases. Binding is due to both ionic and hydrophobic interactions. Thioflavin is an inefficient photosensitizer for the oxidation of histidine but the photosensitizing power of thioflavin increases considerably when the dye is bound to polynucleotides. These effects are interpreted in terms of a stabilization of the excited singlet and triplet states of the dye in the bound state.

Metabolic responses of folic acid and related compounds to thyroxine in rats.

This study deals with the effects of thyroidectomy and feeding thyroid powder on histidine and folic acid metabolism. Normal rats maintained on a soy protein diet, low in methionine but supplemented with vitamin B-12, oxidize approx. 10% of an injected dose of [2-14C]histidine in 3 h and excrete low levels of formiminoglutamic acid. Addition of methionine increases histidine oxidation to approx. 20%. The feeding of thyroid powder or the injection of high levels of thyroxine decreases histidine oxidation and increases formiminoglutamic acid excretion. Surgical thyroidectomy at weaning increases histidine oxidation to approx. 45% and, thus, resembles the effect of methionine in promoting histidine oxidation and decreasing formiminoglutamic acid excretion. The feeding of methionine to the thyroidectomized animal further increases histidine oxidation to 65%. The distribution of folate forms in the liver was determined by column chromatography following administration of a dose of tritiated folic acid. In the normal animal, tetrahydrofolate accounts for 38% of the total folate present. The feeding of methionine increases this to 48%, which is consistent with the observed increase in histidine metabolism. Thyroidectomy increases the percentage of tetrahydrofolate to 63% and the feeding of methionine further increases it to 68%. The percentage of tetrahydrofolate relative to total folate is in proportion to the observed rate of histidine metabolism. The action of thyroidectomy in increasing histidine oxidation may be accounted for by its effect in increasing the proportion of tetrahydrofolate.

Kinetic and mechanistic studies on the oxidation of arginine and histidine by chloramine-T in hydrochloric acid medium

The oxidation of amino acids by chloramine-T (CAT) in HCl medium at 30°C indicates simultaneous catalysis by H+ and Cl− ions in the HCl concentration range of 0.04–0.12 M. The reaction is first order with respect to concentrations [CAT], [H+] and [arginine], but zero order with respect to [histidine]. The rate depends also on Cl− concentration following 0.7th order. At HCl concentrations >0.12 M, the rate equation is:w=k[CAT] [amino acid]0.6 and is independent of the [Cl−]. A suitable mechanism has been suggested.

Reaction of ozone with protease inhibitors from bovine pancreas, egg white, and human serum

Ozone inactivates the bovine pancreas trypsin-kallikrein inhibitor. Tyrosine and methionine residues are oxidized. When methionine is completely oxidized and 0.5 of the four tyrosine residues is oxidized, 90% of the inhibitor capacity is retained. When both methionine and tyrosine residues are completely oxidized, 37% of the inhibitor capacity is retained. For 50% loss of anti-trypsin activity, 62 moles of 0 3/mole of protein were required. Inhibition of the chicken ovomucoid proteinase inhibitor by ozone is accompanied by oxidation of tyrosine, histidine, and methionine residues. For 50% loss of anti-trypsin activity, 32 moles of O 3/mole of protein were required. Anti-trypsin activity of diluted human serum was only slightly inhibited by ozone. Purified α-1-antiprotease from human serum was 50% inactivated by 88 moles of O 3/mole of protein. The oxidation of free tyrosine by ozone proceeds by way of dihydroxyphenylalanine and dihydroxyphenylalanine quinone, finally yielding colored polymeric material.

A D-amino acid oxidase from Chlorella vulgaris

A procedure has been developed for the partial purification from Chlorella vulgaris of an enzyme which catalyzes the formation of HCN from d-histidine when supplemented with peroxidase or a metal with redox properties. Some properties of the enzyme are described. Evidence is presented that the catalytic activity for HCN formation is associated with a capacity for catalyzing the oxidation of a wide variety of d-amino acids. With d-leucine, the best substrate for O 2 consumption, 1 mol of ammonia is formed for half a mol of O 2 consumed in the presence of catalase. An inactive apoenzyme can be obtained by acid ammonium sulfate precipitation, and reactivated by added FAD. On the basis of these criteria, the Chlorella enzyme can be classified as a d-amino acid oxidase (EC 1.4.3.3). Kidney d-amino acid oxidase and snake venom l-amino acid oxidase, which likewise form HCN from histidine on supplementation with peroxidase, have been compared with the Chlorella d-amino acid oxidase. The capacity of these enzymes for causing HCN formation from histidine is about proportional to their ability to catalyze the oxidation of histidine.

Effect of methionine on the metabolism of formate and histidine by rats fed folate/vitamin B-12-methionine-deficient diet.

The metabolism of formate and histidine were compared in rats and in perfused livers of rats on diets deficient in vitamin B-12, methionine, and folic acid. Excretion of formate and formiminoglutamic acid, and the oxidation of [2-14C]histidine and [14C]formate to 14CO2 were measured. Liver folate levels decreased to 40% of normal on the vitamin B-12- and methionine-deficient diets but the rate of oxidation of histidine to CO2 in the whole animal decreased to 15% of normal. This indicated a reduction in the metabolic activity of the liver folates in vitamin B-12deficiency. Comparison of formate and histidine catabolism in folic acid deficiency showed that the oxidation of histine was decreased to 5% of normal but formate oxidation was decreased to only 30% of normal. This indicates that 25% of formate oxidation normally proceeds by a non-folate-dependent pathway.

Photosensitized inactivation of stem bromelain. Oxidation of histidine, methionine, and tryptophan residues.

Pineapple stem bromelain was photooxidized in the presence of Methylene Blue used as a sensitizer. The essential sulfhydryl group of the enzyme protein rapidly became inaccessible to react with 5,5'-dithiobis(nitrobenzoic acid), but the reactivity was readily regained to the original level upon treatment with dithiothreitol. Even after such reduction, the photooxidized enzyme showed a markedly decreased hydrolytic activity on casein. Spectral examination revealed that the oxidized enzyme had tyrosine residues intact. Amino acid analysis showed significant decreases in histidine, ethionine, and tryptophan residues. Photoinactivation occurred in a similar manner also in the presence of tetrathionate which reversibly blocked the essential sulfhydryl group. It is concluded that the irreversible photoinactivation of stem bromelain must be related to the oxidation of histidine, methionine, and tryptophan residues. When the photooxidation was carried out a different pH values ranging from 4.0 to 8.3, the inactivation and the decrease in histidine content were found to be markedly pH dependent. Thus, the photooxidation experiment provided a method for directly measuring the apparent pKa of the ionization of the single histidine residue in stem bromelain. Apparent pKa values of 6.4 and 7.1 were obtained for the histidine imidazole in the absence and in presence of tetrathionate, respectively. In view of these normal pKa values for an imidazole, a mechanism of ionization of the active-site group in a plant thiol proteinase is proposed, in which the validity of mechanism involving a close electronic interaction between histidine and cysteine residues is seriously questioned.