In situ kinetic parameters of glucose-6-phosphatase in the rat liver lobulus.

G.N Jonges,C.J Van Noorden,W.H Lamers

doi:10.1016/s0021-9258(18)42912-2

Abstract

Glucose-6-phosphatase activity has been determined in periportal and pericentral zones of the rat liver lobule using a quantitative histochemical method. The study was performed on unfixed cryostat sections of livers from fasted and fed female and male rats. Highest activity was found in periportal zones, and starvation caused a 2-3-fold increase of glucose-6-phosphatase activity in periportal and pericentral zones of both sexes. Unexpectedly, KM values were also significantly different in periportal and pericentral zones and were found to increase linearly with Vmax values, irrespective of sex and feeding condition. Because the cryofixation procedure was shown to permeabilize the biomembranes in the tissue sections, it can be concluded that the rise in KM and Vmax values has to be attributed to the catalytic unit of the glucose-6-phosphatase system. It is suggested that the enzyme exists in a high affinity configuration at low enzyme concentrations but that at high enzyme concentrations a hysteretic mechanism, as proposed by Berteloot et al. (Berteloot, A., Vidal, H., and Van de Werve, G. (1991) J. Biol. Chem. 266, 5497-5507), transforms the enzyme from a high to a low affinity configuration. The present study indicates that the concept of functional heterogeneity of liver parenchyma may be more complex than thus far assumed.

Highlights

Glucose-6-phosphataseactivity has been determined investigate the exact character of the multicomponent gluin periportalandpericentralzonesoftherat liver cose-6-phosphatase enzyme system
Livers from normally fed female and male rats showed a higher zero-order glucose-6-phosphatase activity in periportal zones than in pericentral zones (Fig. IA).After starvation, Many conditions have tobe fulfilled before the tion of a n enzyme histochemical reaction yields formation [32]
Cytophoto- phosphatase activity that uissed in the presenitnvestigation metric analysis of glucose-6-phosphatase activity in the sections confirmed the qualitative interpretation (Table I)

Summary

Introduction

Glucose-6-phosphataseactivity has been determined investigate the exact character of the multicomponent gluin periportalandpericentralzonesoftherat liver cose-6-phosphatase enzyme system. Before decapitation under ether anesthesia at 11a.m., six males and six females were starved for 24 h in order to obtain high glucose-6phosphatase activity in the liver [25];the other animalswere normally fed. The mean standard error of the mean (S.E.) was calculated both for periportal and pericentral zones; per rat and per zone, five cytophotometricreadings were madeineach of three sections.

Results

Conclusion