EFFECT OF INHIBITORS OF CELL-ENVELOPE SYNTHESIS ON BETA-SITOSTEROL SIDE-CHAIN DEGRADATION BY MYCOBACTERIUM SP NRRL-MB-3683

The role of the lipid bilayer and the peptidoglycan of the mycobacteri al cell wall in the permeation of p-sitosterol into the cell and its t ransformation to androst-1-ene-3,17-dione (AD) and androsta-1,4-diene- 3,17-dione (ADD) was studied. Specific inhibitors were used at concent rations affecting the biosynthesis of the assumed target structures, b ut causing only partial cell growth inhibition or exerting no effect o n growth. m-Fluorophenylalanine and DL-norleucine which are known to d isorganize the biosynthesis of amphipatic components of the outer laye r of the lipid bilayer, used at concentrations 250 mu g/ml and 400 mu g/ml, respectively, increased the formation rate of AD+ADD from 0.3 (c ontrol) to 0.7 and 0.8 mg products/g dry weight/h. The disorganization of the underlying mycolyl-arabinogalactan structure by the action of ethambutol at the concentration 40 mu g/ml, at which the cell growth w as apparently not affected, caused the decrease of the product formati on from 135 mg/l to 70 mg/l. In the presence of isoniazid (350 mu g/ml ) only trace amounts of AD accumulated during 48 hours of transformati on indicating much lower activity than that of the intact cells. The m ost effective among the tested inhibitors of peptidoglycan synthesis w ere glycine (15 mg/ml) and vancomycin (150 mu g/ml) which enhanced the transformation activity of the treated cells nearly three times. Incr eased transformation rate was also obtained by the action of colistin at concentrations ranging from 10 mu g/ml to 15 mu g/ml.