Mass spectrometric analysis of fluorescent products originating from the molybdenum cofactor

Mass spectra of 4 fluorescent HPLC fractions originating from the molybdenum cofactor in xanthine oxidase extracts have been obtained with the method of field desorption (FD). The most polar fraction contains compounds which show peaks in the M/Z = 110-230 and M/Z = 580-750 range. Two other fractions exhibit in the FD spectra peaks at M/Z = 1,113 and M/Z = 886, respectively. Both corresponding compounds contain at most 24 C atoms and lack S, Mo, Cl and Br, as judged from the isotopic pattern. The most apolar fluorescent compound, which could be isolated only from xanthine oxidase extracts prepared in the absence of phosphate, has been identified as a species with a molecular weight around 482.