Reappraisal of the effect of Ca2+ on the activity of liver microsomal glucose-6-phosphatase.
It has recently been reported that free Ca2+, a second hormonal messenger in the liver, can modulate the activity of liver glucose-6-phosphatase by inhibition (van de Werve, G. (1989) J. Biol. Chem. 264, 6033-6036) or activation (Yamagushi, M., Mori, S., and Suketa, Y. (1989) Chem. Pharm. Bull. (Tokyo) 37, 388-390). Such a controversial role for Ca2+ is reinvestigated by comparing the effect of the addition of free Ca2+ (10(-10) to 20.10(-3) M) under the form of CaCl2 or of Ca-EGTA buffers. We show that the glucose-6-phosphatase activity is: 1) increased in the presence of CaCl2 at concentrations higher than 10(-4) M and unaffected in the presence of CaCl2 at lower concentrations; 2) decreased in the presence of Ca-EGTA buffers yielding free Ca2+ concentrations higher than 10(-8) M; 3) the latter effect is not depending on free Ca2+ or free EGTA concentrations, but on Ca.EGTA complex concentration. In addition, these effects can be reproduced in the same concentration ranges by MgCl2 and Mg-EDTA buffers, respectively. It is concluded that a physiological role for free Ca2+ on the activity of liver glucose-6-phosphatase remains to be established.
Mithieux
G
G
Institut National de la Santé et de la Recherche Médicale, Unité 197, Faculté de Médecine Alexis Carrel, Lyon, France.
Vega
F
F
Beylot
M
M
Riou
J P
JP
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002122:Calcium Chloride / Q000494:pharmacology; D002458:Cell Fractionation; D004533:Egtazic Acid / Q000494:pharmacology; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains
D015636:Magnesium Chloride; D004533:Egtazic Acid; D005952:Glucose-6-Phosphatase; D002122:Calcium Chloride; D002118:Calcium