Appearance of a second form of hepatic glycerol-3-phosphate dehydrogenase during neonatal development in the mouse

Livers of 4-day-old Balb/c mice contain a single form of glycerol-3-phosphate dehydrogenase (GPDH, sn-glycerol-3-phosphate:NAD 2-oxido-reductase, EC 1.1.1.8), which is designated GPDH I. The amount of hepatic GPDH I declines during maturation and levels off by about 6–7 weeks of age. During neonatal development a second form of the enzyme, GPDH II, appears. In mature Balb/c mice (6–7 weeks of age) GPDH II comprises about 30% of the total hepatic GPDH activity. Half-maximal levels of GPDH II are attained by about 18 days postpartum. The rate of appearance of GPDH II is not affected by premature weaning. Hepatic GPDH II is chromatographically distinct from hepatic GPDH I or the embryonic isozyme observed in neonatal brains. Thermal denaturation studies indicate that GPDH I and II from Balb/c mice are denatured at 50 °C with a half-time of about 2 min while the embryonic isozyme is denatured with a half-time of about 30 s. GPDH I and II isolated from C57BL6 mice are denatured at 50 °C with a half-time of 6 min while forms I and II from DDS mice are denatured with a half-time of about 12 min. Kinetic studies reveal that GPDH II and the embryonic isozyme have similar apparent affinities for NADH and dihydroxyacetone phosphate. The apparent affinity of GPDH I for NAD, NADH, dihydroxyacetone phosphate, and glycerol-3-phosphate is lower than that of GPDH II.