Histidinol phosphate

This pyridoxal-phosphate-dependent enzyme [EC 2.6.1.9], also called imidazolylacetolphosphate aminotransferase and imidazole acetolphosphate transaminase, catalyzes the reversible reaction of histidinol phosphate with a-ketoglutarate (or, 2-oxoglutarate) to produce 3-(imidazol-4-yl)-2-oxopropyl phosphate and glutamate. 

This enzyme [EC 3.1.3.15] catalyzes the hydrolysis of histidinol phosphate to generate histidinol and orthophosphate. 

HISTIDINOL-PHOSPHATE PHOSPHATASE HISTIDYL-tRNA SYNTHETASE HISTONE KINASE Hofmann rule,... 

GLYCOGEN PHOSPHORYLASE HISTIDINOL-PHOSPHATE PHOSPHATASE myo-INOSITOL 1-MONOPHOSPHATASE... 

SL-histidinol phosphate aminotransferase histidinol phosphate phosphatase ( histidinol dehydrogenase... 

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.

Values are for the specific activity of histidinol phosphate phosphatase relative to the level in the parent strain grown on minintal salts-glucose. The data are taken from Klopotowski and Ames [1171 and Roth et al. [15]. 

ATP phosphoribosyltransferase 2 phosphoribosyl-ATP pyrophosphatase 3 phosphoribosyl-AMP cyclohydrolase 4 isomerase 5 formyltransferase, inosine monophosphate cyclohydrolase 6 adenylosuccinate synthetase 7 adenylosuccinate lyase 8 adenylate kinase 9 imidazole glycerol phosphate dehydratase 10 histidinol phosphate aminotransferase 11 histidinol phosphatase 12 histidinol dehydrogenase... 

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 imidazole acetol phosphate to histidinol phosphate is catalyzed by a transaminase. This pyridoxal phosphate enzyme reacts... 

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. 

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