Coupling quotients derived from stable isotope fractional enrichment data
CPCs derived from WT or db/db CPCs were cultured in growth medium containing [U-13C]glucose. After 18 h, the cells were collected, and the polar and nonpolar fractions were assessed for 13C incorporation in nucleotides and lipids, respectively. A relative coupling quotient between the PPP and the GLP was calculated by dividing the fractional enrichment values of the m + 5 13C isotopologue in the purines ATP and GTP and the pyrimidine UTP by the m + 3 isotopologue of glycerol in phosphatidylinositol (PI). The data represent three replicate samples/group.