Fig 1: Impaired insulin secretion in a subject with glucokinaseE442*.Homeostatic model assessment of β-cell (HOMAβ, a) and C-peptide-to-glucose ratio (b) were reduced in a subject with E442* glucokinase mutation compared with two controls with WT glucokinase. Lower HOMAβ indicates reduced ability to secrete insulin after fasting state (a). The C-peptide-to-glucose ratio is one of the markers demonstrating efficiency of insulin secretion32 (b). c L-arginine-induced insulin secretion was reduced in NIT-1 cells that expressed E442* and E442/3R mutant glucokinase by transfecting with pCDNA-GCK-HA and insulin expression vectors. d G6P production in response to L-arginine was reduced in NIT-1 cells that expressed E442* and E442/3R mutant glucokinase by transfecting with pCDNA-GCK-HA and insulin vectors. Data represent the mean ± S.E. (n = 3). *p < 0.05 (n = 6).