Control of 5-aminolaevulinate synthetase activity in Rhodopseudomonas spheroides a role for trisulphides.

1. The aminolaevulinate synthetase activator of fresh extracts of semi-anaerobically grown Rhodopseudomonas spheroids was resolved into two fractions by ion-exchange chromatography. One fraction was identified as cystine trisulphide (CySSSCy). Analysis of the other fraction indicated the presence of about equal amounts of glutathione trisulphide (GSSSG) and the mixed trisulphide of glutathione and cystine (GSSSCy). 2. Four further fractions with activator activity were observed on ion-exchange chromatography of extracts prepared by methods similar to those described earlier [Neuberger et al. (1973)Biochem. J. 136,491-499]. These activators were generated by the extraction procedure. Two of them have been identified as trisulphanedisulphonate (S5O62-) and additional cystine trisulphide. 3. For the series of polysulphanedisulphonates (-O3S-Sn-SO3-, n greater than or equal to 1), activator activity at muM concentrations was exhibited only by compounds with n greater than 3. This, together with the results described above, indicates that for a compound R-Sn-R' (where R and R' are organic or inorganic groups) the only structural requirement for activity is n greater than or equal to 3. 4. Oxygenation of a semipanaerobic culture of R. spheroids for 1.5h before harvesting the cells produced a decrease of more than 90% in the cellular content of cystine trisulphide and glutathione trisulphides. 5. Chromatography on DEAE-Sephadex confirmed the presence of multiple forms of aminolaevulinate synthetase in extracts of R. spheroides [Tuboi et al. (1970) Arch.Biochem. Biophys. 138,147-154]. Oxygenation of a semi-anaerobic culture resulted in the disappearance of high-activity enzyme (a-form) and the accumulation of low-activity enzyme (b-form) in the cell. Spontaneous activation [Marriott et al. (1969) Biochem. J. 111,385-394] And activation by cystine trisulphide both resulted in the almost complete conversion of the b-form into the a-form.