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

A creatine analogue, beta-guanidinopropionic acid (beta-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 (Vmax) and apparent Michaelis constant for free ADP (Km), 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 microM). As a result of the diet, Vmax was significantly increased (P < 0.05) while Km remained unchanged at around 20 microM. Citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase activities were significantly increased (both P < 0.05). Vmax 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 beta-GPA feeding in EDL muscle was essentially due to a general increase in mitochondrial enzyme concentrations.