Regulation of liver microsomal inorganic pyrophosphate-glucose phosphotransferase, glucose-6-phosphatase and inorganic pyrophosphatase

Abstract

Levels of liver inorganic pyrophosphate-glucose phosphotransferase, acid inorganic pyrophosphatase, and glucose-6-phosphate phosphohydrolase (EC 3.1.3.9) have been assayed in normal, alloxan-diabetic, adrenalectomized and cortisone-treated adrenalectomized rats. Assays were carried out in the absence of added detergent, and with homogenates which had been supplemented with sodium deoxycholate or Triton X-100 to final concentrations of 0.004%, 0.012%, 0.04%, 0.20%, and 0.40%, w/v (deoxycholate) or v/v (Triton). Increases in levels of all activities were observed in the absence of detergent in cortisone-treated adrenalectomized rats compared with untreated adrenalectomized animals, and in diabetic compared with normal rats. Both detergents activated all three activities in all groups of animals. However, basic differences in the modes of response of these activities to cortisone administration as contrasted with insulin deprivation were apparent when assays were conducted with detergent-supplemented homogenates. As detergent concentration was increased, a progressive diminution was noted in the ratios of activity in cortisone-treated compared with untreated adrenalectomized animals. Statistically significant differences in activity level values for the two groups of animals disappeared when deoxycholate concentrations were 0.20% or 0.40%; Triton X-100 also effected a marked diminution in activity level ratios under these conditions. In contrast, differences between comparable activity level values for diabetic compared with normal animals were progressively magnified with increasing concentration of both detergents. These observations indicate that the detergent effects involved are general in nature, and point up the complexity of mechanisms involved in responses of activities of this enzyme to hormonal manipulations. They also raise a question as to the conditions which properly should be employed to assess also raise a question as to the conditions which properly should be employed to assess alterations in functional levels, in vivo, of these activities in future horm and nutritional studies.