Open AccessCharacteristics and specificity of the inhibition of liver glucose‐6‐phosphatase by arachidonic acid
Author(s) -
MITHIEUX Gilles,
BORDETO JeanClaude,
MINASSIAN Carol,
AJZANNAY Ahmed,
MERCIER Isabelle,
RIOU JeanPaul
Publication year - 1993
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1993.tb17782.x
Subject(s) - nordihydroguaiaretic acid , arachidonic acid , microsome , chemistry , enzyme , lipoxygenase , biochemistry , bovine serum albumin , fatty acid , metabolism , glucose 6 phosphatase , medicine , prostaglandin , albumin , endocrinology , biology
The effect of arachidonic acid (δ 4 Ach) on liver glucose‐6‐phosphatase (Glc6 P ase) has been studied in vitro using untreated and detergent‐treated microsomes prepared from fed and 48‐h‐fasted normal rats and from streptozotocin‐induced diabetic rats. Glc6 P ase of both untreated and detergenttreated microsomes (60 μg. protein/ml) is inhibited by δ 4 Ach in a dose‐dependent manner between 10–100 μM. The inhibition is very rapid and does not depend on preincubation of microsomes in the presence of δ 4 Ach. It does depend on the concentration of microsomal membranes and on the concentration of glucose 6‐phosphate: it is more pronounced at low Glc6 P concentrations than at high. As a cosequence, the enzyme displays sigmoidal kinetics in the presence of δ 4 Ach. Hill coefficients (equal to 1 in the control experiments) of about 1.4 were determined in the presence of 50 μM δ 4 Ach, indicating a clear positive cooperative dependency of the Glc6 P ase upon its substrate in the presence of δ 4 Ach. The δ 4 Ach inhibition is fully reversible in the presence of bovine serum albumin. The inhibition does not depend on the metabolism of δ 4 Ach through the prostaglandin synthase (cyclooxygenase) or arachidonate 12‐lipoxygenase pathways since it is not affected by indomethacin and nordihydroguaiaretic acid. Several other unsaturated fatty acids are able to inhibit the enzyme within the same concentration range. In contrast, saturated fatty acids, the arachidonic acid methyl ester and numerous other lipid compounds containing esterified unsaturated fatty acids do not inhibit Glc6 P ase within the same concentration range. The enzyme of fed rats was inhibited in the same manner as the enzyme of 48‐h‐fasted rats. However, Glc6 P ase of untreated microsomes from diabetic rats was less inhibitable by δ 4 Ach than the Glc6 P ase of normal rats. This difference does not persist after solubilization of the membrane lipids by detergent treatment.