Control of δ-aminolevulinate synthetase activity in Rhodopseudomonas spheroides: II. Requirement of a disulfide compound for the conversion of the inactive form of fraction I to the active form

Abstract

The inactive form of Fraction I of δ-aminolevulinate synthetase of R. spheroides was converted to the active form by incubation with low molecular weight substance(s) and a protein fraction which were contained in cell extracts of R. spheroides. The low molecular weight substances could be prepared from cell extracts by treatment with trichloroacetic acid (TCA) or Sephadex G-25 column. By fractionation of the TCA soluble fraction by paper chromatography, three active fractions were obtained. All three fractions were shown to have a disulfide bond. Moreover, the TCA-soluble fraction could be replaced by some disulfide compounds such as l-cystine, d, l-homocystine, d-pantethine, oxidized glutathione and lipoic acid. The optimal pH for the activation reaction was about 6.7. The protein fraction required for the activation, though not well identified yet, appeared to function as a modifying enzyme in the conversion of the inactive form of Fraction I to the active form in the presence of disulfide compounds. 14C-Cysteine moiety was not incorporated into the activated Fraction I when the inactive form was incubated with 14C-cystine in the presence of the activating protein fraction, suggesting that the activation of the inactive form is not associated with the incorporation of cysteine into the enzyme protein.