threo-Pentulose; a 2-ketopentose. l-X. appears in the urine in cases of essential pentosuria; it is also an intermediate in the glucuronate pathway. SYN: xyloketose.
- x. 5-phosphate the d-isomer is an intermediate in the pentose phosphate pathway and in transketolization.
- x. reductase an enzyme that reversibly converts x. to xylitol using either NADH (d-x. reductase) or NADPH (l-x. reductase); a deficiency of the l form is seen in individuals with essential pentosuria. SYN: xylitol dehydrogenase.
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xy·lu·lose 'zīl-(y)ə-.lōsalso -.lōz n a ketose sugar C5H10O5 of the pentose class that plays a role in carbohydrate metabolism and is found in the urine in cases of pentosuria
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xy·lu·lose (ziґlu-lōs) a ketopentose epimeric with ribulose at the 3 carbon, occurring naturally as both the D- and L- isomers. The latter is excreted in the urine in essential pentosuria; the former, phosphorylated at the 5 carbon (D-xylulose 5-phosphate), is an intermediate in the pentose phosphate pathway.Medical dictionary. 2011.