TABLE 1.

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.

Pathway couple	Metabolite couple	WT	db/db
PPP:GLP	ATP (5):PI (glycerol)	4.82 ± 0.13	3.04 ± 0.25a
	GTP (5):PI (glycerol)	4.25 ± 0.05	2.80 ± 0.13a
	UTP (5):PI (glycerol)	4.71 ± 0.10	2.00 ± 0.07b

^a p ≤ 0.01 versus WT CPCs.

^b p ≤ 0.001 versus WT CPCs.