Biosynthesis of membrane-derived oligosaccharides: a periplasmic phosphoglyceroltransferase.

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Abstract
Membrane-derived oligosaccharides (MDO) are glucose-containing constituents of the periplasmic space of Escherichia coli whose biosynthesis is closely linked to the metabolism of membrane phospholipids. A periplasmic enzyme that catalyzes the transfer of phosphoglycerol residues between species of MDO or to certain glucose-containing model substrates such as gentiobiose (6-O-.beta.-D-glucopyranosyl-D-glucose) was discovered. The partially purified enzyme has an apparent MW of about 56,000 in gel permeation chromatography and has an absolute requirement for divalent cations, of which Mn2+ is most active. Although the transferase activity appears to be the physiological function of the enzyme, at low concentrations of acceptor, the enzyme acts as a cyclase, with the liberation of cyclic 1(3),2-phosphoglycerol. A mechanism is suggested for the enzyme.