Lipoate metabolism in Pseudomonas putida LP: thiolsulfinates of lipoate and bisnorlipoate.

Lipoate thiolsulfinate and two bisnorlipoate thiolsulfinates, as well as the previously identified products of β-oxidation (bisnorlipoate, tetranorlipoate, and β-hydroxybisnorlipoate), were isolated and identified as catabolites of ¹⁴C]lipoate from cultures of Pseudomonas putida LP, an organism capable of growth on lipoic acid as a sole source of carbon and sulfur. The newly identified metabolites were characterized by ion-exchange and paper chromatography and infrared, ultraviolet, and mass spectroscopies. Comparison of the isolated catabolites with synthetic standards implies that the lipoic thiolsulfinate isolated is the S-1 monoxide of 1,2-dithiolane-3-valeric acid; one bisnorlipoic thiolsulfinate isolated is the S-1 monoxide, the other apparently the S-2 monoxide. Metabolic studies with P. putida show that lipoate thiolsulfinate is taken up by this microorganism in an energy-dependent process, but less readily than lipoate; lipoate thiolsulfinate supports oxygen consumption in short-term experiments but does not support growth. These results are interpreted as meaning that the thiolsulfinates are “dead-end” metabolites, not intermediates in the sulfur metabolism of this organism. Lipoate thiolsulfinate is not detectably β-oxidized to bisnorlipoate thiolsulfinate under the usual culture conditions.