Glycerol phosphate pathway origin

The monoacylglycerol pathway has also been demonstrated in the adipose tissue of the hamster and the rat. Under certain conditions it appears to compete with the glycerol phosphate pathway for acyl groups and may serve to regulate the activity of the latter pathway. The origin of the monoacylglycerol substrate in adipose tissue is not known. 

Independent of the actual mechanism, functional divergence between two proteins with a common ancestor is exemplified in the /la-barrel structures of N-(phosphor-ibosyl-formimino)-aminoimidazole-carboxamide ribonucleotide isomerase (HisA) and imidazole glycerol phosphate synthase (HisF) of the histidine biosynthetic pathway [16]. The hypothesis of a common origin of the two enzymes was formulated based on sequence comparison [17] and has recently found support by the identification of extensive structural similarities [18],... 

The intrinsic differences of the physicochemical properties (for instance the solubilities) of racemates and pure enantiomers of biomolecules are responsible for the multiple origins of biomolecules. This aspect requires further intense research into the individual pathways. The origin of the chiral and biologically important glycerol-3-phosphate molecule remains unknown. 

However, failing incoporations of C-labeled aeetate and sueeessful ones of Relabeled glycerol as well as pyruvate in hopanes and ubiquinones showed isopen-tenyldiphosphate (IPP) to originate not only from the acetate mevalonate pathway, but also from activated acetaldehyde (C2, by reaction of pyruvate and thiamine diphosphate) and glyceraldehyde-3-phosphate (C3) R. In this way, 1-deoxy-pentulose-5-phosphate is generated as the first unbranched C5 preeursor of IPP. 

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