Yeast histidine pathway

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dehydratase and histidinol phosphatase in extracts from the shoots of barley, oats, and peas, and to the unpublished observations of Davies (see Davies, 1971) on the presence of histidinol dehydrogenase in rose tissue culture cells.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. 

The his4 region of yeast [11], and the equivalent genes in Neurospora [13,66-68) and Aspergillus [69], specify three of the enzymic activities in the histidine pathway, the second, third, and tenth steps (Fig. 9). The... 

Our understanding of the enzymology of thiamin biosynthesis in bacteria is now at an advanced level the complete biosynthetic pathway in B. mbtilis has been reconstimted and all of the required enzymes have been structurally and mechanistically characterized. Thiazole formation in yeast is also relatively well understood. The formation of the thiamin pyrimidine in yeast is still poorly understood apart from the identification of PLP and histidine as precursors, nothing is known about the mechanistic enzymology of this complex process and... 

Figure 9.20 Pathways for election transfer in a modified cytochrome c. The diagram shows the structure of a ruthenated His-62 mutant yeast iso-1-cytochrome c, including the positions of some of the aminoacid residues (histidine, etc.). The His-62 group is ruthenated and electron transfer takes place from Ru. to the haem group (the position of the metal atom is marked by a cross). Possible pathways are shown by dashed and dotted lines. From Ref. [34,f. ...

The aromatic amino acid L-phenylalanine (primary metabolite) is directed into the phe-nylpropanoid pathway leading to hydroxy-cinnamic acids, lignin and flavonoids by the activity of L-phenylalanine ammonia-lyase (PAL), which brings about its nonoxidative deamination yielding ammonia and tvans-cinnamic acid (Fig. 1). PAL is one of the most studied plant enzymes, and its crystal structure has recently been solved [2]. PAL is related to the histidine and tyrosine ammonia-lyases of amino acid catabolism. A class of bifunctional PALs found in monocotyle-donous plants and yeast can also deaminate tyrosine [3]. A single His residue is responsible for this switch in substrate preference [3, 4]. All three enzymes share a unique MIO (4-methylidene-imidazole-5-one) prosthetic group at the active site. This is formed auto-catalytically from the tripeptide Ala-Ser-Gly by cyclization and dehydration during a late... 

As is the case in decarboxylation reactions involving malic acid, histidine, and tyrosine, degrading arginine provides yeasts with additional energy resonrces. The net energy gain via the arginine pathway consists of a molecnle of ATP produced from carbamyl-P. 

Candida yeast species. At the molecular level, amitrole stimulates the transcription of the arom gene in Saccharomyces cerevisiae, probably as a cross-pathway response to histidine starvation. ... 

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