1. Glycerol-3-phosphate dehydrogenase of insect thoracic muscle mitochondria and arylsulphatase C of rat liver microsomes were inhibited by anionic surface-active agents oleate, palmitoylCoA and sodium dodecylsulphate, and activated by cationic surfactants cetyltrimethylammonium bromide and cetylpyridinium chloride. Dimethylaniline oxidase of rat liver microsomes, monoamine oxidase of rat liver mitochondria and acetylcholinesterase of rat brain microsomes were inhibited by cationic surfactants and activated by anionic surfactants. The inhibition of NADH dehydrogenase of rat liver submitochondrial particles by NAD + was potentiated by the anionic surfactants and partly released by cetyltrimethylammonium bromide.2. These surface-active activators and inhibitors altered apparent K, values of the enzymes but did not change the activities at infinite substrate concentration (I/ values).3. This effect of surfactants disappeared after solubilization of the membranes and re-appeared after incorporating the solubilized enzyme into phospholipid vesicles.4. Cationic surfactants decreased whereas anionic surfactants increased the negative surface charge and surface potential of mitochondria, submitochondrial particles and microsomes, as measured by free electrophoresis of the particles and binding of 8-anilino-l-naphthalene sulphonate.

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The accumulation of carnitine was measured in cerebral cortex neurons isolated from adult rat brain. This process was found to be lowered by 40% after preincubation with ouabain and with SH-group reagents (N-ethylmaleimide and mersalyl). The initial velocity of carnitine transport was found to be inhibited by 4-aminobutyrate (GABA) in a competitive way (K i 20.9^2.4 mm). However, of various inhibitors of GABA transporters, only nipecotic acid and very high concentrations of 1-[2-([(diphenylmethylene)amino]oxy)ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride (NO-711) acid decreased carnitine accumulation while betaine, taurine and b-alanine had no effect. The GABA transporters expressed in Xenopus laevis oocytes did not transport carnitine. Moreover, carnitine was not observed to diminish the accumulation of GABA in cerebral cortex neurons, which further excluded a possible involvement of the GABA transporter GAT1 in the process of carnitine accumulation, despite the expression of this protein in the cells under study. The absence of carnitine transporter OCTN2 in rat cerebral cortex neurons (K. A. Naøe Îcz, D. Dymna, J. E. Mroczkowska, A. Broe Èr, S. Broe Èr, M. J. Naøe Îcz and R. Cecchelli, unpublished results), together with the insensitivity of carnitine accumulation towards betaines, implies that a novel transporting protein is present in these cells.