Histidine Histidinol

The biosynthesis of pilocarpine in Pilocarpus pennatifolius was studied by the administration of radiolabeled precursors. Radioactive sodium acetate, histidine, histidinol, methionine, and threonine were administered by the cut-stem method. Histidine, methionine, and threonine were administered together by a wick inserted through the stem of an intact plant. Sodium acetate and histidine were fed to root cuttings by suspending the roots in aqueous solutions of the precursors. After 64 - 7 5 h, the roots were harvested and total alkaloid extracts made. These extracts were then fed to stem cuttings. 

Histidine, histidinol, histamine, urocanic acid, and imidazole-pyruvic, -acetic, and -lactic acids were recovered from rumen fluid and separated on an aminopropyl column (Jl = 220 nm). Elution was complete in 25 min using a 21/79 water (67 mM K2HPO4 at pH 6.45)7(90/10 acetonitrile/water) mobile phase [1430]. Excellent resolution was achieved and peak shapes were excellent except for a very broad imidazolepyruvic acid peak. Decreasing pH increased retention for the analytes. The authors also noted that frequent rinsing of the system with phosphate buffer solution only was needed. A linear range of 1-500 pM along with detection limits of 0.8-5 pM (analyte dependent) were reported. 

This enzyme [EC 1.1.1.23] catalyzes the reaction of l-histidinol with two NAD+ to produce L-histidine and two NADH. L-Histidinal will also serve as a substrate for this protein. The Neurospora crassa enzyme will also catalyze the reactions of phosphoribosyl-AMP cyclohydrolase [EC 3.5.4.19] and phosphoribosyl-ATP pyrophosphatase [EC 3.6.1.31]. 

HISTAMINE N-METHYLTRANSFERASE HISTIDINE AMMONIA-LYASE DEHYDROALANINE HISTIDINE DECARBOXYLASE Histidine decarboxylase reduction, BOROHYDRIDE REDUCTION HISTIDINOL DEHYDROGENASE... 

Hansen BS, Vaughan MH, Wang LJ. 1972. Reversible inhibition by histidinol of protein synthesis in human cells at the activation of histidine. J Biol Chem 247 3854-3857. (Mechanistic study validating the use of amino-alcohols as AA-synthetase inhibitors)... 

Auch L-Histamin und L-Histidinol bilden reversibel oxygenierbare Kobalt(II)-Komplexe (75). Die Carboxylfunktion des dreizahligen Ligan-den Histidin ist demnach kein notwendiges Strukturelement fiir die Oxygenierung. 

Evidence for the presence of the enzymes of the histidine pathway in plants appears to be limited to the work of Winter et al. (1971a) who demonstrated the presence of ATP-phosphoribosyltransferase, the first enzyme of the pathway, imidazole glycerolphosphate dehydratase and histidinol phosphatase in extracts from the shoots of barley, oats, and peas, and to the unpublished observations of Davies (see Davies, 1971) on the presence of histidinol dehydrogenase in rose tissue culture cells. The specific activity of ATP-phosphoribosyltransferase was greatest in peas and oats and least in barley. The enzymes from oats and barley were thermolabile losing activity after 30 min at 37°C. The specific activities of imidazole glycerolphosphate dehydratase were very low but it was possible to purify the enzyme to some extent. The values for imidazole glycerolphosphate for the barley enzyme was 0.6 mM which compares with values for jthe yeast and bacterial enzymes of 0.3 and 0.4 mM, respectively. Histidinolphosphatase was purified 20-fold but the authors considered that two phosphatases were still present. 

Fig. 2. The pathway of histidine biosynthesis. Enzymes a, ribosephosphate pyrophos-phokinase E.C. 2.7.6.1 b, ATP-phosphoribosyltransferase, E.C. 2.4.2.17 c, phosphoribosyl-AMP cyclohydrolase, E.C. 3.5.4.19 d, N-(5 -phospho-D-ribosylforminino)5-amino-l-(5"-phos-phoribo yl)-4-imidazole carboxamide isomerase, E.C. 5.3.1.16 e, glutamine amidotransferase f, imidazolglycerolphosphate dehydratase E.C. 4.2.1.19 g, histidinol-phosphate aminotransferase E.C. 2.6.1.9 h, histidinol phosphatase, E.C. 3.1.3.15 i, histidinol dehydrogenase, E.C. 1.1.1.23.

Figure 5.82 Biosynthesis of histidine. PRPP, 5-phosphoribosyl-a-l-pyrophosphate PRATP, AT-5 -phosphoribosyl-ATP PRAMP, M-S -phosphoribosyl-AMP 5 -ProFAR, yV -[(5. phosphoribosyl)-formimino]-5-aminoiinidazole-4-carboxamide-ribonucleotide 5 -PRFAR, A/ -[(5 -phosphoribulosyl)-formimino]-5-aminoimidazole-4-carboxainide-ribonuc leotide IMGP, imidazole glycerol-phosphate AICAR, 5 -phosphoribosyl-4-carboxamide-5-aminoimidazole lAP, imidazoleacetol-phosphate HOL-P, L-histidinol-phosphate HOL, L-histidinol HAL, L-histidinal.

B. Phosphoribosyi ATP pyrophosphohydroiase (EC 2.4.2.17). In /Veurospors this enzyme is trifunctional, also catalysing reaction A and the conversion of histidinol to histidine (Fig. 1). 

Isotopic studies with labeled potential precursors such as sodium acetate- " C, threonine- C, histidine- " C, histidinol- " C, and L-methionine-(S-methyl- " C) were carried out with P. pennatifolius in an attempt to prove the proposed pathways [8, 39]. Only the methylation of pilocarpidine, last step in both mechanisms, was attested by significant incorporation of radioactivity in the methyl group attached to the imidazole nucleus. This data confirmed an important assumption, the one that considers methionine the biological source of the A -methyl group of pilocarpine. Also, one should consider that these radiolabeled studies were carried out with stems, no other parts of the plant were analyzed, and thus some other site involved in biosynthesis was not considered in this study. 

A transaminase isolated from Neurospora reacts with certain substrates which do not contain carboxyl groups, but have phosphate esteri-fied to the carbon adjacent to that bearing the amino group (11). Histidinol phosphate, histidine, arginine, glutamic acid and their keto analogs react with this enzyme. 

The conversion of histidinol phosphate to histidine requires removal of the phosphate group free histidinol was the first precursor of histidine established in genetic studies. The hydrolysis of histidinol phosphate is catalyzed by a phosphatase that has recently been purified by Ames from Neurospora extracts. This enzyme is active with histidinol phosphate as a substrate, but has very little, if any, activity with a number of phosphate esters, including the other imidazole compounds involved in histidine biosynthesis. At least one less specific phosphatase occurs in Neurospora histidinol phosphate is also hydrolyzed nonspecifically, but the activity of the nonspecific hydrolytic enzyme is slow compared with the specific histidinol phosphatase. The nonspecific reaction may account for the slow growth of mutants deficient in the specific enzyme. The specific enzyme is quite insensitive to beryllium and chelating agents, which inhibit nonspecific phosphate hydrolysis. 

Histidinol is oxidized to histidine by a dehydrogenase that appears to catalyze both steps required. - The most definitive studies on this dehydrogenase were carried out with preparations of Arlhrobacter hi i-dinolovorans, a soil organism isolated by an enrichment technique using histidinol as a carbon and nitrogen source. Similar enzymes occur in E. coli and yeast. Two equivalents of DPNH are produced in this reaction. The reduction of the first mole of DPN by these enzymes should result in the formation of the aldehyde, histidinal. This compound, however, has not been detected in incubation mixtures, even when aldehyde binders were added. Histidinal, an unstable compound in neutral solution, does serve as a substrate for the dehydrogenase, with both DPN... 

L-Histidinol (III), isolated from an E. coli histidine mutant, stands apart from the other compounds in that it was found that it was utihzed slowly by another histidineless E. coli mutant and, furthermore, by selection from this second mutant, a strain was obtained which utihzed the L-histidinol 75% as well as histidine. This suggests that not histidinol but its phosphate ester is the true intermediate. 

Mutants of E. coli which are auxotrophic for histidine accumulate L-histidinol, the corresponding aminoalcohol. Mutants of Neurospora have been discovered since, which accumulate not only histidinol but also... 

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