Conformation of ribonuclease S-protein.

Ribonuclease S-protein exhibits a pH-dependent conformational transition between folded and unfolded states, and some unfolded S-protein persists up to pH 8. The histidine C2 proton resonance of the unfolded species was erroneously assigned by Bradbury et al. to histidine residue 119 of the folded species.     

Gastrin: obligatory intermediate in the postprandial mobilization of gastric histamine in the rat.

In unoperated fasted rats, feeding raised the serum gastrin concentration, reduced the gastric mucosal histamine content and activated the gastric histidine decarboxylase. The reduction of gastric histamine and activation of histidine decarboxylase was induced also by the injection of pentagastrin. In antrectomized rats, feeding failed to produce these effects. Injection of pentagastrin, however, still lowered gastric histamine and activated gastric histidine decarboxylase. Thus, antral gastrin seems to be an obligatory mediator of the postprandial activation of histidine decarboxylase and mobilization of histamine.     

Conformation of ribonuclease S-protein

Summary Ribonuclease S-protein exhibits a pH-dependent conformational transition between folded and unfolded states, and some unfolded S-protein persists up to pH 8. The histidine C2 proton resonance of the unfolded species was erroneously assigned by Bradbury et al. to histidine residue 119 of the folded species.     

Gastrin: Obligatory intermediate in the postprandial mobilization of gastric histamine in the rat

Summary In unoperated fasted rats, feeding raised the serum gastrin concentration, reduced the gastric mucosal histamine content and activated the gastric histidine decarboxylase. The reduction of gastric histamine and activation of histidine decarboxylase was induced also by the injection of pentagastrin. In antrectomized rats, feeding failed to produce these effects. Injection of pentagastrin, however, still lowered gastric histamine and activated gastric histidine decarboxylase. Thus, antral gastrin seems to be an obligatory mediator of the postprandial activation of histidine decarboxylase and mobilization of histamine.Acknowledgments. Grant support from the Swedish and Danish Medical Research Councils (14P-4822, 04X-1007, 17X-4144 and 512-2540).     

Colchicine inhibits stimulated release of gastric histamine but not activation of histidine decarboxylase.

In the rat, gastric mucosal histamine is mobilized and histidine decarboxylase activated by treatment with insulin or pentagastrin. Colchicine pretreatment prevented the histamine release without preventing the enzyme activation. The results suggest a) that histamine release and histidine decarboxylase activation are independent events, and b) that microtubules are involved in the release of histamine.     

Colchicine inhibits stimulated release of gastric histamine but not activation of histidine decarboxylase

Summary In the rat, gastric mucosal histamine is mobilized and histidine decarboxylase activated by treatment with insulin or pentagastrin. Colchicine pretreatment prevented the histamine release without preventing the enzyme activation. The results suggest a) that histamine release and histidine decarboxylase activation are independent events, and b) that microtubules are involved in the release of histamine.     

The amino acid composition of histidine ammonialyase from Pseudomonas putida NCIB 10807.

The amino acid composition of histidine ammonia-lyase from Pseudomonas putida NCIB 10807 suggests that this enzyme may be different from the Pseudomonas testosteroni NCIB 10808 histidine ammonia-lyase, whose amino acid composition is known.     

Histamine formation by ruminal fluid from cattle in vitro

Summary Net histamine formation in ruminal fluid is shown to be the result of histidine decarboxylation and histamine deamination. Addition of 4.7 mM histidine increased the rate of net histamine synthesis by a factor of 20 compared to normal. Histamine production sharply decreases at pH values below the physiological range.     

Histidine-induced injury to cultured liver cells,effects of histidine derivatives and of iron chelators

The amino acid histidine is an excellent buffer and is therefore included in several organ preservation solutions used in transplantation medicine. However, when used at concentrations as in these solutions, histidine has a marked injurious potential. Therefore, we here assessed the mechanism of histidine-induced cell injury and searched for ways to use the buffering power of histidine but avoid histidine toxicity. When cultured hepatocytes were incubated in HTK solution or in modified Krebs-Henseleit buffer containing 198 mM L-histidine at 37°C, most cells lost viability within 3 h (LDH release 86 ± 7% and 89 ± 5%, respectively). This injury was accompanied by marked lipid peroxidation, and was strongly inhibited by hypoxia, by the antioxidants trolox, butylated hydroxytoluene and N-acetylcysteine and by the membrane-permeable iron chelators 2,2′-dipyridyl, 1,10-phenanthroline, LK 614, LK 616 and deferoxamine. Thus, histidine-induced cell injury appears to be mediated by an iron-dependent formation of reactive oxygen species. D-Histidine, imidazol and L-histidine methyl ester also elicited marked injury, while the N-substituted derivatives Nα-acetyl-L-histidine and tert-butyl-oxycarbonylhistidine and histidine-containing dipeptides showed almost no toxicity. Histidine toxicity, its iron dependence and the superiority of Nα-acetyl-L-histidine were also evident during/after cold (4°C) incubations. Therefore, we suggest the addition of iron chelators to histidine-containing solutions, and/or replacing histidine with Nα-acetyl-L-histidine in organ preservation solutions. Received 23 October 2006; accepted 21 November 2006     

The amino acid composition of histidine ammonialyase fromPseudomonas putida NCIB 10807

Summary The amino acid composition of histidine ammonia-lyase fromPseudomonas putida NCIB 10807 suggests that this enzyme may be different from thePseudomonas testosteroni NCIB 10808 histidine ammonia-lyase, whose amino acid composition is known.Acknowledgment. I wish to thank the Department of Biochemistry and Biophysics, Leeds University, England, for the use of their excellent laboratory facilities.     

Liminal gastrin does not activate rat stomach histidine decarboxylase

Summary Fasted rats have a low gastric histidine decarboxylase activity. I.v. infusion of heptadecapeptide gastrin for 2 h raised the enzyme activity. Intragastric perfusion with the same dose of gastrin and for the same period of time did not reproduce the effect of circulating gastrin. It is concluded that luminal gastrin, in contrast to circulating gastrin, does not activate rat stomach histidine decarboxylase.This study was supported by the Swedish Medical Research Council (04X-1007, 14X-4144) and by the Albert Påhlsson Foundation.     

Activities of kidney decarboxylases of histidine and ornithine in adrenalectomized mice substituted with cortisone.

In adrenalectomized mice, cortisone inhibited histidine decarboxylase of the kidney in a dose-related manner. The effect of cortisone on ornithine decarboxylase was diphasic: small doses elevated, high doses inhibited.     

Spin label studies of ATP phosphoribosyltransferase of E. coli.

Covalently bound bromoacetamide nitroxides have been used to detect the conformational changes and enzyme association induced by its feedback inhibitor, histidine.     

Effects of cysteine and N-acetyl cysteine on GSH content of brain of adult rats

Intraperitoneal injections of cysteine or N-acetyl cysteine induce a depletion of reduced glutathione (GSH) in rat brain. The doses required to promote GSH depletion are lower than those reported to cause a disseminate neurodegenerative syndrome. Since physiological GSH concentrations are required to maintain cell membranes, we suggest that consideration of the cysteine-induced GSH depletion is important in attempts to understand the mechanism of cysteine-induced cytotoxicity in brain.     

Photo-oxidation of histidine as a probe for aminoterminal conformational changes during fibrinogen-fibrin conversion

Fibrinogen is known to become unclottable when irradiated with light in the presence of methylene blue, the loss of clottability being due to photo-oxidation of the histidine at position 16 of the B<beta> chain. In the present investigation it could be demonstrated that not only this histidine but also the one at position 24 of the A<alpha> chain was modified and that the rates of modification could be modulated by fibrinopeptide release, polymerization inhibition and denaturation. Accordingly, the histidine modifications can be used as probes for surface accessibility of and conformational differences among the various forms of the protein. Both histidines are shielded by the fibrin polymer structure. Fibrinopeptide A release alone leads to maximal protection of the one in the A<alpha> chain, but only partial protection of the one in the B<beta> chain. Subsequent fibrinopeptide B release leads to maximal protection of the one in the B<beta> chain. The differential effects indicate that two conformational changes have occurred. Polymerization inhibition reverses the protective effect. Denaturation leads to maximal and equal modification in all samples as a consequence of the loss of native conformation. Received 8 October 1996; accepted 15 October 1996     

Inhibition of tumor promotion by a lecanoric acid analogue

3',5'-Dichloro-2,4'-dihydroxybenzanilide, an inhibitor of histidine decarboxylase, inhibited skin tumor promotion induced by 12-O-tetradecanoylphorbol-13-acetate in mice.     

Photochemical oxidation of actinidin,a thiol protease fromActinidia chinensis

Summary Actinidin was rapidly inactivated by methylene blue-catalyzed photooxidation at pH 7.9 and 20°C. The rate of inactivation was pH-dependent and became slower at lower pH values, suggesting the involvement of a histidine residue in the inactivation.     

Synthesis of histidine2-angiotensin II analogues.

The synthesis of histidine2-angiotensin II analogues, namely H-Asp-alpha-(im-Bzl)His-Val-Tyr-Ile-(im-Bzl)His-Pro-Phe-OH and H-Asp-beta-(im-Bzl)His-Val-Tyr-Ile-(im-Bzl)His-Pro-Phe-OH, are described. Also a new route leading to the synthesis of alpha-benzyl-L-aspartate, using N-trityl-L-aspartate di-benzyl ester as the starting material, is reported.     

The effect of thiazol-4-ylmethoxyamine,a histidine decarboxylase inhibitor,on the development of morphine tolerance and physical dependance in mice

Summary A new histidine decarboxylase inhibitor, thiazol-4-ylmethoxyamine (TMA), injected into mice in a dose of 100 mg/kg i.p. 48 h before the implantation of a morphine-containing pellet, inhibited the development of morphine tolerance and physical dependence.I thank the World Health Foundation (Hong Kong) for a grant in aid of this research.