Glucosamine Research Today is a free monthly online journal that collates and summarizes the latest research about Glucosamine, including details on chondroitin sulfate, uses, effects, benefits, arthritis. | ||||||||
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Gene expression patterns and catalytic properties of UDP-D-glucose 4-epimerases from barley (Hordeum vulgare L.).Zhang Q, Hrmova M, Shirley NJ, Lahnstein J, Fincher GB
UDP-D-Glucose 4-epimerase (EC 5.1.3.2) catalyzes the interconversion of UDP-D-galactose and UDP-D-glucose. Both nucleotide sugars act as activated sugar donors for the biosynthesis of cell wall polysaccharides such as cellulose, xyloglucans, (1,3; 1,4)-beta-D-glucan and pectins, together with other biologically significant compounds including glycoproteins and glycolipids. Three members of the barley UDP-D-glucose 4-epimerase gene family, designated HvUGE1, HvUGE2 and HvUGE3, have been characterized. Quantitative real time PCR showed that HvUGE1 mRNA was most abundant in leaf tips and mature roots, but its expression levels were relatively low in basal leaves and root tips. The HvUGE2 gene was transcribed at significant levels in all organs examined, while HvUGE3 mRNA levels were very low in all organs. Heterologous expression of a near full-length cDNA confirmed that HvUGE1 encodes a functional UDP-D-glucose 4-epimerase. A non-covalently bound NAD + was released from the enzyme after denaturing with aqueous ethanol and was identified by its spectrophotometric properties and by electrospray mass spectrometry. The K m values were 40 muM for UDP-D-galactose and 55 muM for UDP-D-glucose. The barley UDP-D-glucose 4-epimerase also catalyzes the interconversion of UDP-N-acetyl-D-galactosamine and UDP-N-acetyl-D-glucosamine, although it is not known if this has any biological significance. A three-dimensional model of the barley UDP-D-glucose 4-epimerase revealed that its overall structural fold is highly conserved compared with the human UDP-D-galactose 4-epimerase and provides a structural rationale for its ability to bind UDP-N-acetyl-D-glucosamine. Published 3 November 2005 in Biochem J.
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