UDPG

D-Galaktose entsteht nach L. F. Leloir in der Natur aus D-Glucose durch enzymatische Konfigurationsumkehr des C-4 auf der Stufe der a-1-Phosphate. Die Enzyme, die diese Inversion vollbringen, benotigen als Cofaktor Uridin-diphosphat-glucose (UDPG). Nun konnte. aus... 

In general, microsomes/S9 and cofactor (NADPH or UDPG A) are the most costly components of an incubation, but substrate, especially for early discovery compounds, is sometimes scarce. Higher enzyme concentration will lead to higher volume productivity and less amount of the cofactor to maintain the same cofactor concentration. However, the relationship of reaction rate and enzyme concentration may not be linear, so a higher enzyme concentration may yield lower enzyme productivity (amount of product per milligram enzyme used). Therefore, different protein concentration levels should be screened to obtain a good balance between volume and enzyme productivities. 

GUO, L., POULTON, J.E., Partial purification and characterization of Arabidopsis thaliana UDPG Thiohydroximate glucosyltransferase, Phytochemistry, 1994, 36, 1133-1138. 

UDPG was the first of a whole new class of nucleotides, in which the uridine diphosphate group is attached to a monosaccharide. Two important members of the class are uridine diphosphate glucuronic acid, the intermediate in the synthesis of glucuronides and of many other compounds, and uridine diphosphate N-acetylglucosamine which is an intermediate in the synthesis of mucopolysaccharides. Uridine diphosphate muramic acid was isolated by Park (P2) from Staphylococcus aureus... 

Gal-l-P + UDPG = G-l-P + UDPGal Galactose-l-phosphate uridyl transferase... 

UDPGal = UDPG Uridine diphosphate galactose 4-epimerase... 

UDPG + PP = G-l-P + UTP Uridine diphosphate glucose pyro-phosphorylase... 

The key metabolite, UDPG, is largely synthesized by reaction (4), the enzyme being abundant in many tissues. Since reactions (3) and (4) are reversible, the body does not need exogenous galactose to form UDPGal and, hence, the many important compounds made from it. 

Subject Liver homogenate ((imoles 1-C14-Gal-1-P incorporated into nu-eleotides/g liver/hour) Erythrocyte hemolyzate (nmoles UDPG utilized/ml red blood cells/hour) In vivo galactose metabolism (g/hour)... 

Diagnosis UDPG consumption Specific and reliable for diagnostic purposes UV Spectrophotometer (A2)... 

Diagnosis UDPG consumption Modification of 2., giving visible color change can be applied to technics 3., 5. and 9. Absorptiometer (400 mu) (N4)... 

Detection of heterozygote UDPG consumption Measures rate of reaction can combine with estimation of UDPGal formation good discrimination heterozygotes from normals UV Spectrophotometer (B17)... 

Monitoring of treatment UDPG consumption (no Gal-l-P added) Resembles 2. estimates Gal-l-P present in erythrocytes UV Spectrophotometer (Kll)... 

Walker et al. (Wl) used a UDPG consumption test combining the features described by Bretthauer et al. (B17) and by Anderson et al. (A2). Overlap between the values for heterozygotes and for normals found by Walker et al. was intermediate between the amount of overlap found by the method of Bretthauer et al. and by that of Anderson et al. 

In a further modification, Nordin and Bretthauer (N4) assay the residual UDPG by incubation with TNDPN. The final optical density is read at 400 mp, making an ultraviolet spectrophotometer unnecessary. 

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