STUDIES ON THE PRODUCTION OF (S)-(-SOLKETAL (2,2-DIMETHYL-1,3-DIOXOLANE-4-METHANOL) BY ENANTIOSELECTIVE OXIDATION OF RACEMIC SOLKETAL WITH COMAMONAS-TESTOSTERONI())

All strains of Comamonas testosteroni investigated here, produced quin ohaemoprotein ethanol dehydrogenase (QH-EDH) when grown on ethanol or butanol, but one strain of C. acidovorans and of C. terrigena did not. Hybridization experiments showed that the gene for QH-EDH is absent i n the latter two strains. Induction and properties of the QH-EDHs seem to be similar: all C. testosteroni strains produced the enzyme in its ape-form [without pyrroloquinoline quinone (PQQ)] and the levels were higher at growth at low temperature; preference for the R-enantiomer and similar selectivity was shown in the oxidation of solketal (2,2-di methyl-1,3-dioxolane-4-methanol) by cells (supplemented with PQQ); the fragment of the qhedh gene gave high hybridization with the DNA of th e C. testosteroni strains. Experiments with C. testosteroni LMD 26.36 revealed that the organism is well suited for production of (S)-solket al: it shows an adequate enantioselectivity (E value of 49) for the ox idation of racemic solketal; the conversion rate of (R)-solketal is on ly 3.5 times lower than that of ethanol; the optimal pH for conversion (7.6) is in a region where solketal has sufficient chemical stability ; separation of the remaining (S)-solketal from the acid formed is sim ple; induction of QH-EDH, the sole enzyme responsible for the oxidatio n of (R)-solketal, occurs during growth on ethanol or butanol so that the presence of solketal (inhibitory for growth) is not required; prod uction of active cells and the conversion step can be integrated into one process, provided that PQQ and solketal addition occur at the appr opriate moment; the conversion seems environmentally feasible. However , since high concentrations of solketal inhibit respiration via QH-EDH , further investigations on the mechanism of inhibition and the stabil ity of the enzyme might be rewarding as it could lead to application o f higher substrate concentrations with consequently lower downstream p rocessing costs.