Order of enzymic incorporation of O-methyl groups into the O-methyl- d-glucose-containing polysaccharide of Mycobacterium smegmatis. A tritium-labelling study

Abstract

The order of enzymic incorporation of O-methyl groups into the O-methyl- d-glucose-containing polysaccharide (MGP) of Mycobacterium smegmatis, 3MG(J)→G(I)→G(H)→G(G)→6MG(F)→(GMG) 9(E)→[G(L)→G(D)]→G(C)→[G(K)→G(B)]→G(A)→Ga, where G is d-glucose, 3MG is 3- O-methyl- d-glucose, 6MG is 6- O-methyl- d-glucose, and Ga is d-glyceric acid, was studied by incubating cultures of M. smegmatis with l-[ 3H- Me]methionine for various times. MGP was then extracted from the cells, and relative radioactivities of residues D, ( E + F) average and J, or of D, E average, F, and J, were determined. Tritium-labelling of these residues increased in the reducing-to-nonreducing residue direction, the steepness of the gradient becoming more shallow with increasing incubation time. The results are consistent with a biosynthetic mechanism that involves sequential addition of O-methyl groups to residues of the pre-formed d-glucan, in the reducing-to-non-reducing residue direction.