| Popis: |
A multienzyme catalyzing the formation of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine, the first free intermediate in penicillin biosynthesis, was detected in an assay measuring the formation of tripeptide from L-[U-14C]valine in the presence of L-alpha-aminoadipic acid, L-cysteine, ATP, Mg2+ ions, and dithioerythritol. Enzyme was extracted from dry mycelium using a buffer with a high glycerol concentration and thiol protective agent to stabilize enzyme activity. In five steps the enzyme was purified 118-fold. It catalyzed ATP-pyrophosphate exchange in dependence of all three constituent amino acids, and the enzyme could be amino-acylated with L-[14C]valine. The molecular weight of the protein both native (in gel filtration chromatography) and denatured (polyacrylamide gel electrophoresis) was about 220 kDa. These data suggest that delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase consists of a single polypeptide chain and a multienzyme thiotemplate mechanism for the reaction sequence is postulated. |
