The effects of colchicine analogues on the reaction of tubulin with iodo[14C]acetamide and N,N'-ethylenebis(iodoacetamide)

We have previously found (Ludue?a, R. F., and Roach, M. C. (1981b) Biochemistry 20, 4444-4450) that colchicine and podophyllotoxin inhibit the alkylation of tubulin by iodo[14C]acetamide and the formation of an intrachain cross-link in the beta-tubulin subunit by N,N'-ethylenebis(iodoacetamide) (EBI). It was not clear whether these effects were due to conformational changes in tubulin induced by drugs or to direct steric blockage of the sulfhydryl groups involved. In an effort to characterize further these phenomena, we have examined the effects of single-ring and bicyclic analogues of colchicine on the reaction of tubulin with iodo[14C]acetamide and EBI. We have found that neither the A-ring analogues, 3,4,5-trimethoxybenzyl alcohol, 3,4,5-trimethoxybenzaldehyde, 2,3,4-trimethoxybenzaldehyde, and benzaldehyde, nor the C-ring analogues, tropolone and tropolone methyl ether, inhibited alkylation. In contrast, colchicine, podophyllotoxin, and nocodazole and the bicyclic analogues, 5-(2',3',4'-trimethoxyphenyl)-2-methoxytropone and combretastatin, inhibited tubulin alkylation. Since the presence of a bond joining the A and C rings seems to be the determining factor in the suppression of alkylation, it is likely that inhibition by colchicine of the reaction with iodo[14C] acetamide is due largely to a conformational change induced by colchicine. A different pattern was obtained when the effects on cross-link formation by EBI were examined. Here, all the A-ring analogues, the bicyclic analogues, and colchicine, podophyllotoxin, and nocodazole all inhibited formation of the cross-link, whereas the C-ring analogue tropolone methyl ether did not inhibit cross-link formation. Since compounds whose effect on alkylation is markedly different have the same effect on cross-link formation, it is possible that this effect is a steric one and that perhaps the A-ring of colchicine binds to tubulin very close to one of the sulfhydryls involved in the intrachain cross-link formed by EBI in beta-tubulin.     

Effect of rhodium (III) complex on experimental carcinogenesis in the livers of rats treated with thioacetamide

Enzyme activities and protein content were determined in the cytosolic and mitochondrial fractions of liver homogenates obtained from Rh(III) complex-, thioacetamide- and thioacetamide + Rh(III) complex-treated rats. The Rh(III) complex administered to nonthioacetamide-treated rats produced no significant changes either in the enzymatic activities assayed or in the protein concentration. The Rh(III) complex administered to thioacetamide-treated rats produced significant restoration of the following altered values: cytosolic and mitochondrial aspartate aminotransferase, glutamate dehydrogenase, NADP-isocitrate dehydrogenase, and protein concentration. However, a further increase was produced in the activities of glucose-6-phosphate dehydrogenase and malic enzyme. These increases can be interpreted in terms of an enhancement of the NADPH-dependent detoxifying processes and of nucleic acid synthesis and repair.     

Selection of Wine Yeasts for Growth and Fermentation in the Presence of Ethanol and Sucrose

To optimize the conversion of carbohydrates to ethanol, strains of several Saccharomyces species were examined for the ability to grow and ferment in a range of sucrose and ethanol concentrations. A total of 632 wine yeasts, most of them isolated from wineries in Andalusia and Extremadura, southwestern Spain, were subjected to screening and selection. Growth and fermentative capacity in different ethanol and sucrose concentrations varied from one strain to another. There was no correlation between growth and fermentative capacity. The best 35 strains grew in 15% ethanol and fermented in 18% ethanol. Ethanol accumulated, although at a reduced rate, after the cells stopped growing. Most yeast strains were highly fermentative in 50% sucrose. Some of them effectively utilized the carbohydrates of the culture, yielding final ethanol concentrations of > 14%. Of the 35 selected strains, 16 were promising for genetic analysis and breeding because of their capacity to sporulate. These strains were homothallic, and their spores were viable. The meiotic products analyzed so far were also homothallic.     

Effects of the new antifungal antibiotic mucidin

The antibiotic activity of the antifungal substance mucidin was compared with the activity of nystatin and pimaricin. The antibiotics were tested by the plate method using 19 fungal species, mainly phytopathogenic ones. Toward 14 species, mucidin was ten times more active than nystatin and pimaricin, toward 5 species the activities were roughly the same. The antibiotics differed also in the sharpness of the inhibition zone boundaries.