Abstract
The polyenzyme complex responsible for the synthesis of tyrocidine in Bacillus brevis (ATCC 8185) was found to contain 4'-phosphopantetheine, which appeared to be connected with the production of growing peptide chains. Confirmation of this assumption has now been obtained by purifying from bacterial lysates a polyenzyme-dissociation product; this was labeled with [(14)C]pantothenic acid and peptide chains containing tritiated amino acids, and had a molecular weight of 17,000. To obtain these results, organisms were grown udner conditions favorable for incorporation of radioactive pantothenic acid into tyrocidine-synthesizing enzymes. A crude lysate of the [(14)C]pantothenic acid-labeled organisms was preincubated with the tritiated amino acids to form enzyme-bound growing peptide chains. The doubly labeled fragments were purified from the polyenzyme-dissociation products produced by prolonged lysis. In a second set of experiments, the three enzymes responsible for tyrocidine synthesis, including the two polyenzymes containing pantetheine, were purified and incubated with radioactive amino acids and ATP to form polyenzyme-bound peptide chains. Thereupon, a Triton X-100 extract of the 20,000 x g fraction of crude homogenate was added to dissociate the purified polyenzymes. The dissociation products were purified and yielded, on dodecyl sulfate gel electrophoresis, peptidyl-marked products ranging in molecular weight from 90,000 to 17,000, the latter being most abundant. Electrophoresis of analogous preparations after preincubation with higher concentrations of dodecyl sulfate and dithiothreitol at 100 degrees yielded a single product of 17,000 molecular weight, indicating that the larger molecular weight fractions were aggregates thereof.