| hexose monophosphate pathway | <biochemistry> A pathway of hexose oxidation in which glucose-6-phosphate undergoes two successive oxidations by NADP, the final one being an oxidative decarboxylation to form a pentose phosphate. Diverges from this when glucose-6-phosphate is oxidized to ribose 5 phosphate by the enzyme glucose-6 phosphate dehydrogenase. This step reduces NADP to NADPH, generating a source of reducing power in cells for use in reductive biosyntheses. In plants, part of the pathway functions in the formation of hexoses from carbon dioxide in photosynthesis. Also important as source of pentoses, for example for nucleic acid biosynthesis. This pathway is the main metabolic pathway in neutrophils, congenital deficiency in the pathway produces sensitivity to infection. Alternative metabolic route to Embden Meyerhof pathway for breakdown of glucose. (18 Nov 1997) |
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| hexose monphosphate pathway | A metabolic pathway present in a wide range of prokaryotic and eukaryotic microorganisms as well as in plants and animals, it involves the oxidative decarboxylation of glucose-6-phosphate, via 6 phosphogluconate, to ribulose 5-phosphate, followed by a series of reversible, non-oxidative interconversions whereby hexose and triose phosphates are formed from pentose phosphates. (09 Oct 1997) |
| hexose | Monosaccharide containing six carbon atoms, for example glucose, galactose, mannose. (18 Nov 1997) |
| hexose-1-phosphate uridylyltransferase | <enzyme> An enzyme that catalyses the transfer of ump from udpglucose to galactose 1-phosphate, forming udpgalactose and glucose 1-phosphate. Deficiency in this enzyme is the major cause of galactosaemia. Chemical name: UDPglucose:alpha-D-galactose-1-phosphate uridylyltransferase Registry number: EC 2.7.7.12 (12 Dec 1998) |
| hexose monophosphate shunt | The main metabolic pathway in activated neutrophils, rendering them relatively insensitive to inhibitors of oxidative phosphorylation. Congenital deficiency of the first enzyme in the shunt, glucose 6 phosphate dehydrogenase, produces a sensitivity to infection similar to that seen in chronic granulomatous disease. (18 Nov 1997) |
| hexose phosphatase | <enzyme> May be an aspect of acid phosphatase, EC 3.1.3.2 Registry number: EC 3.1.3.- (26 Jun 1999) |
| hexose phosphate synthetase | <enzyme> Ribulosephosphate formaldehyde gives d-erythro-l-glycero-3-hexulose Registry number: EC 4.1.2.- Synonym: 3-hexulose phosphate synthase, d-arabino-3-hexulose 6-phosphate formaldehyde-lyase, 3-hexulosephosphate synthase, d-arabino-3-hexulose-6-phosphate-lysase, hexulose-6-phosphate synthase, hump synthase (26 Jun 1999) |
| udpglucose-hexose-1-phosphate uridylyltransferase | <enzyme> An enzyme that catalyses the transfer of ump from udpglucose to galactose 1-phosphate, forming udpgalactose and glucose 1-phosphate. Deficiency in this enzyme is the major cause of galactosaemia. Chemical name: UDPglucose:alpha-D-galactose-1-phosphate uridylyltransferase Registry number: EC 2.7.7.12 (12 Dec 1998) |
| utp-hexose-1-phosphate uridylyltransferase | <enzyme> An enzyme that catalyses the synthesis of udpgalactose from utp and galactose-1-phosphate. It is present in low levels in foetal and infant liver, but increases with age, thereby enabling galactosaemic infants who survive to develop the capacity to metabolise galactose. Chemical name: UTP:alpha-D-hexose-1-phosphate uridylyltransferase Registry number: EC 2.7.7.10 (12 Dec 1998) |
| alternative oxidase pathway | Pathway of mitochondrial electron transport in higher plants, particularly in fruits and seeds, that does not involve cytochrome oxidase and thus is resistant to cyanide. (18 Nov 1997) |
| alternative pathway | See: complement activation. (18 Nov 1997) |
| anabolic pathway | <biochemistry> A reaction or series of reactions in a metabolic pathway that synthesise complex molecules from simpler ones, usually requiring the input of energy. Compare: catabolic pathway. (09 Oct 1997) |
| auditory pathway | Neural paths and connections within the central nervous system, beginning at the organ of Corti's hair cells, continuing along the eighth nerve, and terminating at the auditory cortex. (05 Mar 2000) |
| GABA pathway | The pathway that ultimately converts 4-aminobutyrate to succinate; succinate is then converted to alpha-ketoglutarate, via the tricarboxylic acid cycle, which is then acted upon by glutamate dehydrogenase; glutamate is then decarboxylated to reform 4-aminobutyrate; an important pathway for those cells which make this neuroactive molecule. Synonym: GABA pathway. (05 Mar 2000) |
| Palade pathway | <cell biology> The routing of proteins from the site of their synthesis to the final cellular or secreted position. Several different pathways are known and others suspected. Glycosylation of the proteins may provide specific address labels for the proteins. (18 Nov 1997) |