Kinetic properties of the glucose 6-phosphatase of the liver from arthritic rats.
According to previous reports, adjuvant-induced arthritic rats present reduced activities of the hepatic glucose 6-phosphatase. A kinetic study was done in order to characterize this phenomenon. Microsomes were isolated from livers of arthritic and control rats (Holtzman strain) and the glucose 6-phosphatase was measured at various temperatures (13-37 degrees C) and glucose 6-phosphate concentrations. Irrespective of the temperature, the enzyme from arthritic rats presented a reduction of both V(max) and K(M). Detergent treatment of liver microsomes from control rats increased the activity, but no increase was found when microsomes from arthritic rats were treated in the same way. The mannose 6-phosphatase activity of detergent-treated microsomes from arthritic rats was only 25% of the activity found with detergent-treated microsomes from control rats. Without detergent treatment, the mannose 6-phosphatase activities of both control and arthritic rats were minimal. The activation energy, derived from V(max), was not changed by arthritis. In vivo arthritic rats presented higher hepatic glucose 6-phosphate concentrations, a phenomenon that is consistent with a reduced activity of glucose 6-phosphatase. It was concluded that in arthritic rats, the hydrolase is probably reduced, without a similar change in the translocase activity.
Kelmer-Bracht
Ana Maria
AM
Laboratory of Liver Metabolism, Department of Biochemistry, University of Maringá, 87020900, Maringá, Brazil. abract@uem.br
Santos
Carmem Patrícia Barbosa
CP
Ishii-Iwamoto
Emy Luiza
EL
Broetto-Biazon
Ana Carla
AC
Bracht
Adelar
A
D000818:Animals; D001169:Arthritis, Experimental / Q000201:enzymology*; D003902:Detergents; D005215:Fasting / Q000378:metabolism; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D017830:Octoxynol; D051381:Rats; D017207:Rats, Sprague-Dawley
D003902:Detergents; D017830:Octoxynol; D005952:Glucose-6-Phosphatase