Aminohexuronic acid

A substance later shown to be muramic acid (see Section IV,6) was clearly different from the product of Vi antigen, and, although the strain used in some of the Vi studies (Escherichia coli 5396/38) is one in which sialic acid has been detected, the properties of the Vi antigen are markedly different from the neuraminic acid pol3oner. Infrared spectra recorded for crystalline V-acetyl-neuraminic acid exhibit full detail and cannot be compared with that published for aminohexuronic acid, but that of the amorphous neuraminic acid polymer (colominic acid) is rather similar to that of the Vi antigen polymeric unit, since their functional groups are very similar. The relationship of these substances to the property of 0 -inagglutinability is discussed later (see p. 336). 

Evidence that the repeating unit of this polymer is an aminohexuronic acid has already been described no other component has been reported. 

PolA is responsible for the activation of UMP for accepting the PEP (phospho-enolpyruvic acid) moiety for the eventual formation of 3 -EUMP (3 -enolpyruvyl uridine-5-monophosphate). Dephosphorylation by PolJ (a putative tyrosine phosphatase) and cyclization of 3 -EUMPby PolH would immediately follow the reaction of PolA to generate an intermediate which is then converted to the aminohexuronic acid moiety with stepwise functions of PolK, PolD, and Poll, respectively. This latter proposal results in a slight modification of the previously proposed pathway for the biosynthesis of the polyoxin nucleoside skeleton, whose biosynthesis was proposed to be initiated by uridine and PEP as starting substrates [17]. 

UDP-7V-acetylglucosamine (uridine diphosphate), nikkomycins act as potent competitive inhibitors of chitin synthase and exhibit potent fungicidal, insecticidal, and acaricidal activities [320]. Nikkomycin X and Z, isolated as major components, contain the hydroxypyridylhomothreonine (HPHT) moiety, the aminohexuronic acid, and a nucleoside moiety N-glycosidically linked to 4-formyl-imidazolin-2-one or a uracil base, respectively [321, 322]. 

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