On the possible role of respiratory activity of Acholeplasma laidlawii cells in sugar transport.

1. Out of 20 exogeneous substrates only ethanol and, to a much lesser extent, lactate and pyruvate were shown to be capable of stimulating the respiration of Acholeplasma laidlawii cells. However, none of these substrates changed the initial rate of active transport of 3-O-methyl-D-glucose (3-O-MG). 2. From inhibitory analyses and spectroscopic data, it is apparent that the respiratory chain of A. laidlawii has no cytochromes and is probably not responsible for oxidative phosphorylation. 3. Valinomycin and nigericin stimulated cell respiration only in the presence of K+-ions, while monensin stimulated it in the presence of Na+-ions. 4. 3-O-MG transport was shown to be sensitive to uncouplers, ATPase inhibitors and arsenate are resistant to a majority of respiratory inhibitors tested. This suggested that there was no relationship between respiration and carbohydrate transport in the A. laidlawii cells. Further evidence was provided by the absence of respiratory stimulation during the transport of non-metabolizing carbohydrates.