N and C NMR determination of methionine metabolism in developing soybean cotyledons.

The metabolism of d- and l-methionine by immature cotyledons of soybean (Glycine max, L. cv Elf) grown in culture has been investigated using solid-state (13)C and (15)N nuclear magnetic resonance. d-Methionine is taken up by the cotyledons and converted to an amide, most likely by N-malonylation. About 16% of the l-methionine taken up is incorporated intact into protein, and 25% remains as soluble methionine. Almost two-thirds of the l-methionine that enters the cotyledons is degraded. The largest percentage of this is used in transmethylation of the carboxyl groups of pectin. Methionine is not extensively converted to polyamines. We attribute the stimulation of growth of the cotyledons by exogenous methionine to the bypassing of a rate-limiting methyl-transfer step in the synthesis of methionine itself, and subsequently of pectins and proteins.