ATP synthesis kinetic properties of mitochondria isolated from the rat extensor digitorum longus muscle depleted of creatine with β-guanidinopropionic acid

Abstract

A creatine analogue, β-guanidinopropionic acid (β-GPA), was administered in the food (1% w w ) of 8 male rats while 8 control rats received a standard diet. Mitochondrial oxidative capacity and kinetic parameters of mitochondrial ATP synthesis, apparent maximal ATP synthesis rate ( V max) and apparent Michaelis constant for free ADP ( K m), were investigated in the extensor digitorum longus (EDL) muscle. Mitochondrial ATP synthesis rate was measured by a bioluminescent method over a large range of ADP concentration (2–30 μM). As a result of the diet, V max was significantly increased ( P < 0.05) while K m remained unchanged at around 20 μM. Citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase activities were significantly increased (both P < 0.05). V max was tightly correlated with CS activity ( P < 0.001; r = 0.84). It was concluded that the increase in maximal mitochondrial ATP synthesis rate after β-GPA feeding in EDL muscle was essentially due to a general increase in mitochondrial enzyme concentrations.