Masayuki Uda

Mechanism of membrane damage induced by the amphipathic peptides gramicidin S and melittin

The action of gramicidin S and melittin on human erythrocytes, Staphylococcus aureus and Escherichia coli was studied as an extension of the previous study (Katsu, T., Ninomiya, C., Kuroko, M., Kobayashi, H., Hirota, T. and Fujita, Y. (1988) Biochim. Biophys. Acta 939, 57-63). These amphipathic peptides stimulated the release of membrane phospholipids outside cells in a concentration range causing permeability change. The shape change of erythrocytes from normal discoid to spiculate form was observed just prior to the release of membrane components. We have proposed the following action mechanism of gramicidin S and melittin. The peptide molecules were predominantly accumulated in the outer half of the bilayer, deforming the erythrocyte cell into crenature. A large accumulation made the membrane structure unstable, resulting in the release of membrane fragments and the simultaneous enhancement of permeability. The action mechanism of these peptides was compared with that of simple surfactants.

Structural requirements of alkyl acyldithiocarbazates for the uncoupling of oxidative phosphorylation in mitochondria.

A structure-activity relationship study on the uncoupling of alkyl acyldithiocarbazates was carried out. Greater activity was observed with increasing alkyl chain length, the optimum being C9. A further increase in alkyl chain length caused a decrease in the activity. Thione-thiol tautomeric forms with a dissociable proton were dound to be of primary importance for the uncoupling and the role of the acyl group was auxiliary. The reactivity of the SH group of alkyl acyldithiocarbazates with an SH-reagent was very low. These compounds facilitated the valinomycin-induced swelling of non-respiring mitochondria and non-sonicated lecithin liposomes in isotonic potassium acetate solution.

Ring‐chain tautomerism of aldehyde n‐methylated semicarbazones

Ring-chain tautomerism of thirty-six aldehyde semicarbazones was studied by nmr spectro-scopy. The 2,4-dimethylsemicarbazones of benzaldehyde, p-tolualdehyde, p-anisaldehyde, and P-chlorobenzaldehyde exist as chain forms in DMSO-d6, but as both ring and chain forms in deuteriotriiluoroacetic acid. Unlike these semicarbazones, the aldehyde semicarbazones of N-unsubstituted semicarbazide, 2-methylsemicarbazide, and 4-methylsemicarbazide did not cyclo-isomerize in either DMSO-d6 or deuteriotrifluoroacetic acid. These results indicate that protona-tion of the C=N nitrogen atom and steric hindrance of the 2-methyl group with an aromatic group at the C=N carbon atom in the chain form cause cycloisomerization to ring isomers.

Lipophilic dithiocarbazates as potent uncouplers of oxidative phosphorylation.

Recently, Biiuerlein and Keihl [ 1 ] found that nonyl thiourea and nonyl thiouracil were inhibitors of oxidative phosphorylation, inhibiting the respiration in State 3 and stimulating respiration in State 4, in mitochondria. These effects were ascribed to the direct interaction of a nonphosphorylated highenergy intermediate X-l, with lipophillc thiourea or thlouracil, forming mixed disulfide complex [ 11. Since these compounds contain the common structure -NH-CS-NH-, it is of interest to examine the activities of.dithlocarbazates or dithiocarbamates, on mitochondrial functions, having a similar chemical structure, -NH-CS-S-. We have studied the effects of some alkyl acyldithiocarbazates on mitochondria and found that they are potent uncouplers of oxidative phosphorylation. This paper deals with uncoupling activities of nonyl3-picolinoyldithiocarbazate(PDTC-9; I), nonyl3-nicotinoyldithiocarbazate(NDTC-9; II) and nonyl3-isonicotinoyldithiocarbazate(IDTC-9; III).