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Mitochondrial enzyme activities (cytochrome c-oxidase = COX, carnitine acyl-transferase = CAT, citrate synthase = CS, lipoamide dehydrogenase = lipDH from the pyruvate-dehydrogenase complex, lactate dehydrogenase = LDH, and malate-dehydrogenase = MDH) were measured from progressive myopathy/encephalomyopathy. Cytochrome oxidase (COX) deficiency was detected from muscle or liver tissues, adult type of COX defectus had been diagnosed in 1 case and infantile type in further 6 cases. The 3 familial atactic children showed decreased activity of carnitine acetyl-transferase, too.

In the enzymatic acetylation of para-nitroaniline the esters of para-amino-benzoic acid act as inhibitors since they serve as alternative acceptor substrates. The extent of inhibition is increased by increasing the number of carbon atoms of the alcohol moiety of the esters. The apparent Km value of esters as acceptor substrates decreases by almost one order of magnitude from 1.1 times 10- minus 4 to 2.5 times 10- minus 5 M within the methylester-butylester series. It has been shown by kinetic analyses that the esters are non-competitive inhibitors in respect of the acetyl donor, whereas they are competitive inhibitors in respect of the acetyl acceptor, in the acetylation reaction of paranitroaniline.

At low thiamine pyrophosphate concentrations the time-course of the reaction catalyzed by mammalian pyruvate dehydrogenase complex shows a lag period of some minutes when the reaction is started by either enzyme, pyruvate or thiamine pyrophosphate. However, started by CoASH or NAD+, the lag period disappears. An increase in enzyme concentration to 25 mU/ml causes a concomitant shortening of the duration of the lag period (tau), while above this value tau is independent of the enzyme concentration. An increase in thiamine pyrophosphate concentration decreases the value of tau and the lag period vanishes at infinite thiamine pyrophosphate concentration. It is suggested that both isomerization and aggregation-dissociation reactions may play an improtant role in the development of the lag period of pyruvate dehydrogenase complex.

The ratio of aceytlcarnitine to carnitine was unchanged in the interscapular brown fatty tissue of rats which were kept at 5 degrees C. The quantity of total acid soluble carnitine relative to the fat-free dry weight was also unchanged. On the other hand a small decrease of the environmental temperature from 23 degrees C to 18 degree C and 20 degrees C resulted in a significant increase in the acetylcarnitine to carnitine ratio.

Buformin at a concentration of 1--2.5 mM stimulates solubilized carnitine palmitoyltransferase by reducing the inhibitory effect of palmitoyl-CoA. Neither buformin nor metformin inhibits the solubilized carnitine palmitoyltransferase.

We investigated the effect of denervation upon the concentration of carnitine, the activity of carnitine palmityltransferase and carnitine acetyltransferase in the "red" soleus and "white" extensor digitorum longus muscles of the rat. Soon after denervation a marked drop in the amount of muscle carnitine was observed, that was more pronounced in the "red" soleus. The activity of both CPT and CAT decreased in both types of muscle, but CPT activity decreased to a greater extent in the soleus than in the EDL. These data may be indicative of a more impaired fat combustion in the "red" than in the "white" muscle following denervation.