Glucose-6-phosphate dehydrogenase in small intestine of rabbit: biochemical properties and subcellular localization

Biochemical properties and cellular and subcellular distribution patterns o f glucose-6-phosphate dehydrogenase (G6PD) were investigated in small intes tine of rabbits. The specific activity of G6PD in fresh homogenates of smal l intestine was 19 +/- 9 IU/g protein. This value did not change significan tly after dialysis. The kinetic and electrophoretic properties of the parti ally purified enzyme were similar to those found in other rabbit tissues. E nzyme histochemical. analysis of G6PD activity using the tetrazolium salt m ethod showed high activity in epithelial cells of villi and crypts of Liebe rkuhn. The activity in acinar cells of Brunner's glands was lower than that in epithelium, whereas cells of the muscularis externa showed a very low a ctivity. Immunohistochemical analysis showed that the amounts of G6PD prote in were lower in the epithelium than in Brunner's glands and muscularis ext erna. The differences between distribution patterns of activity and protein of G6PD may reflect the presence of inactive enzyme molecules in Brunner's glands and muscularis externa or posttranslational activation of G6PD in e pithelium. Electron microscopic immunocytochemical analysis performed with gold-labelled antibodies showed the presence of G6PD protein throughout the cytoplasm and at smooth endoplasmic reticulum in enterocytes. In Paneth ce lls and cells of Brunner's glands, G6PD was found in the cytoplasm, at roug h endoplasmic reticulum and Golgi complex. Immunolabelling was not found in mitochondria or nuclei. Our findings show that G6PD is heterogeneously dis tributed in cells of the small intestine and that the enzyme is associated with rough and smooth endoplasmic reticulum to support synthetic functions in these compartments by NADPH production.