The pterin (bactopterin) of carbon monoxide dehydrogenase from Pseudomonas carboxydoflava

Radioactively labeled carbon monoxide (CO) dehydrogenase has been obtained in good yield and purity from Pseudomonas carboxydoflava grown in the presence of [32P]phosphate. One enzyme molecule contained an average of 8.32 molecules of phosphate. The entire phosphate content was confined to 2 molecules of FAD and 2 molecules of a pterin. These were noncovalently bound. Molybdoenzyme cofactors could be extracted into N-methyl formamide; pterins were isolated by thin-layer chromatography. CO dehydrogenase contained a novel pterin, different from molybdopterin, which was also resolved in other bacterial molybdoenzymes. Therefore, it was tentatively named bactopterin. The characteristic features of bactopterin were as follows. (a) A relative molecular mass, Mr, of 730 which was much greater than that of molybdopterin (330) (Mr values refer to molybdenum-free forms of the cofactors; presumably, the latter were also devoid of the sulfhydryl groups contained in the native compounds). (b) A content of 2 molecules of phosphate/molecule compared to only 1 phosphate in molybdopterin. (c) Bactopterin was three times less susceptible to air oxidation than molybdopterin. (d) Native bactopterin was cleaved by perchloric acid into two phosphorous-containing fragments with Mr, of 330 and 420. The smaller one is believed to be very similar to molybdopterin, the larger one was not a pterin but probably contained an aromatic structure.