Biosynthetic and biophysical information from 13C-13C multiplets by 13C nuclear magnetic resonance

Carbon-13 enriched molecules exhibit multiplets due to 13C--13C scalar coupling. Although generally viewed as a complicating factor, these multiplets can be used in a variety of ways to obtain different types of information. Biosynthetic applications are based on the fact that the relative multiplet intensities are related quantitatively to the percent enrichment of the carbons. Thus, 13C enrichment during the course of a biosynthetic experiment can be monitored by an analysis of the 13C--13C multiplet intensities. In addition, multiplet peaks provide a way of measuring a correlation in the 13C labeling of scalar coupled carbons. Biophysical measurements are based on the 13C--13C dipolar coupling which can provide a significant contribution to the relaxation of non-protonated carbons. This technique can be particularly useful for studying internal rotation which will affect the ratio of the 13C--1H to the 13C--13C dipolar coupling. Biosynthetic studies of the photosynthetic fixation of 13CO2 into 2-hydroxy-1-(hydroxymethylethyl) α-D-galactopyranoside [galactosyl glycerol] by species of the marine red alga, Gigartina, were conducted. Algal samples were taken at various times after the initial exposure to 13CO2 and the galactosyl glycerol was extracted. NMR and mass spectrometric measurements indicate that the galactosyl glycerol consists of a pool of unlabeled material and a pool of newly synthesized material, the labeling of which increases as time progresses. Spin lattice relaxation and nuclear Overhauser enhancement measurements of 13C--13C multiplets of 6-phosphogluconate were made