MASS-SPECTROMETRIC STUDIES OF THE PATH OF CARBON IN PHOTOSYNTHESIS - POSITIONAL ISOTOPIC ANALYSIS OF C-13-LABELED 2-OCTULOSE PHOSPHATES

The electron impact mass spectrometric fragmentation patterns of the per-O-trimethylsilyl (TMS) and alkoxime-TMS derivatives of D-glycero-D-altro and D-glycero-D-ido-octuloses were fully analysed using seven specifically labelled C-13 analogues. Many of the more intense ions in the spectra of the per-O-TMS furanose and pyranose derivatives have more than one origin. On the other hand, the mass spectra of the straight-chain methoxime and ethoxime hepta-O-TMS derivatives contain ions each of which in general originates from a single cleavage process. This makes gas chromatography/mass spectrometry of the alkoxime-TMS derivatives a suitable method for monitoring C-13 incorporations at individual carbon atoms in the corresponding octulose phosphates during photosynthesis experiments with (CO2)-C-13.