UDPGal

Other nucleoside diphosphate sugar compounds are known, eg, UDPGal. In addition, the same sugar may be linked to different nucleotides. For example, glucose may be linked to uridine (as shown above) as well as to guanosine, thymidine, adenosine, or cy-tidine nucleotides. 

Reaction (1) is irreversible the enzyme galactokinase has been found in mammalian liver, brain, and erythrocytes, as well as in certain yeasts and other microorganisms. UDPGal, the main product of reaction (2), is the intermediate by means of which the body incorporates galactose into cerebrosides and, probably, other galactolipids, mucopolysaccharides, and lactose galactose-l-phosphate uridyl transferase occurs in the liver, to a lesser extent in red cells, and probably in other tissues. 

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

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

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. 

Isselbacher (13, 14) has shown that mammalian liver and brain, but not red cells, contain an enzyme, UDPGal pyrophosphorylase, which catalyzes the following reaction ... 

A similar reaction had previously been known to occur in Saccharomyces fragilis (K8) and in bean seedlings (N3). This is an alternative route to UDPGal, but the activity of the enzyme in newborn liver is very low even in the adult it is only one-sixth that of galactose-l-phosphate uridyl transferase (13), as shown in Table 2. 

Diagnosis UDPGal formation Modification of 2., more specific requires UDPGal-4-epimerase UV Spectrophotometer (M4)... 

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

Gal-l-P + UDPGlu <-> Glu-l-P + UDPGal Uridyl transferase UDPGal <-> UDPGlu UDPglucose epimerase (Inversion of configuration on C4)... 

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