Fig. 2.

Abundance of enzymes and lipid carrier intermediates in the lipid II cycle. a Pool level distribution of lipid II cycle intermediates and rate of PG synthesis predicted by the theoretical model for E. coli. b The surface concentration (number of enzymes per unit surface area) of the PG synthesis machinery is similar in Gram-positive and -negative organisms. c Increased catalytic rates of the lipid II cycle enzymes are expected to significantly speed-up the PG synthesis in Gram-positive organisms. As the catalytic rate k_cat = k₂ also affects the Michaelis constant K_M, an increase in the speed of an enzymatic reaction can decrease the affinity of the enzyme for its substrate. d Pool level distribution of lipid II cycle intermediates and rate of PG synthesis predicted by the theoretical model for B. subtilis. The significantly thicker PG layer in B. subtilis, which compensates the lack of an outer membrane, demands an increase in the rate of PG synthesis, implying higher levels of lipid II intermediates shuttling faster through the cycle