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.

Transport of 3-0-methyl-D-glucose (3-0-MG) by Acholeplasma laidlawii cells was studied. The 3-0-MG transport system appeared to be constitutive in cells grown on 3-0-MG and glucose; the transport process depended on the concentration of substrate used and exhibited typical saturation kinetics, with an apparent Km of 4.6 MM. 3-0-MG was transported as a free carbohydrate and was not metabolized further in the cell. Dependence on pH and temperature and the results of efflux and "counterflow" experiments demonstrated the carrier nature of the transport system. 6-Deoxyglucose and glucose competitively inhibited 3-0-MG transport, whereas maltose inhibited it non-competitively. p-Chloromercuribenzoate, p-chloromercuribenzene sulfonate, N-ethylmaleimide, and iodoacetate inhibited transport of 3-0-MG. Cells were able to accumulate 3-0-MG against a concentration gradient. Some electron transfer inhibitors (rotenone and amytal), arsenate, dicyclohexylcarbodiimide, and proton conductors such as 2,4-dinitrophenol, carbonylcyanide, m-chlorophenylhydrazone, pentachlorophenol, and tetrachlorotrifluoromethylbenzimidazole inhibited this process.of the assay mixture were removed from the test tubes 1 on August 5, 2020 by guest