FIG. 3.

Generalized FAS-II elongation module of M. tuberculosis for the synthesis of meroacids. The substrates are R-CO-S-ACP and malonyl-S-ACP derived from malonyl-S-CoA by FabD. R, long-chain alkyl group. Enzymes involved in these reactions are as follows: 1, β-ketoacyl-ACP synthase (KasA/KasB); 2, β-ketoacyl-ACP reductase; 3, β-hydroxyacyl-ACP dehydrase; 4, 2-trans-enoyl-ACP reductase (InhA). The product of the last reaction undergoes the next cycle of elongation as the ACP derivative on another FAS-II module. This is a long-chain fatty acid elongation system in which the hydrocarbon chain is increased by two carbons with the completion of each cycle. t, trans isomer.