The metabolism of acetate and mevalonic acid by lactobacilli III. Studies on the unsaponifiable lipids derived from mevalonic acid

Abstract

In an investigation of the synthesis of the unsaponifiable lipids of Lactobacillus casei from mevalonic acid, it was shown that although no preferential order of synthesis of the components could be detected there was a turnover of the principal one with a simultaneous increase in the others. The presence of glucose and of all the amino acids was found to be necessary for the incorporation of mevalonic acid by L. casei and L. arabinosus. Since, in addition, the incorporation of mevalonic acid was inhibited by chloramphenicol it appears that protein synthesis is necessary for the uptake of mevalonic acid. This requirement for protein synthesis could not be explained by the necessity for inducing an enzyme before mevalonic acid could be utilised by the bacteria. Of other inhibitors tested, only p-chloromercuribenzoate completely inhibited the incorporation of mevalonic acid. Analysis of the cell fractions, prepared by differential centrifugation, suggested that the lipid from mevalonic acid is located in the soluble fraction of the cell. Only a trace of this lipid was found in the protoplast membrane of Micrococcus lysodeikticus. The unsaponifiable lipids could not replace mevalonic acid or acetate in the growth of L. acidophilus and they were not incorporated into the cell lipids by L. casei, L. arabinosus or L. acidophilus. The effect of mevalonic acid deficiency on the incorporation of various radioactive biochemicals was investigated and glucose uptake was found to be significantly reduced. A smaller reduction was found in the rate of acid production.