Drug residue formation from ronidazole, a 5-nitroimidazole. III. Studies on the mechanism of protein alkylation in vitro

Ronidazole (1-methyl-5-nitroimidazole-2-methanol carbamate) is reductively metabolized by liver microsomal and purified NADPH-cytochrome P-450 reductase preparations to reactive metabolites that covalently bind to tissue proteins. Kinetic experiments and studies employing immobilized cysteine or blocked cysteine thiols have shown that the principal targets of protein alkylation ara cysteine thiols. Furthermore, ronidazole specifically radiolabelled with 14C in the 4,5-ring, N-methyl or 2-methylene positions give rise to equivalent apparent covalent binding suggesting that the imidazole nucleus is retained in the bound residue. In contrast, the carbonyl-14C-labeled ronidazole gives approx. 6--15-fold less apparent covalent binding indicating that the carbamoyl group is lost during the reaction leading to the covalently bound metabolite. The conversion of ronidazole to reactive metabolite(s) is quantitative and reflects the amazing efficiency by which this compound is activated by microsomal enzymes. However, only about 5% of this metabolite can be accounted for as protein-bound products under the conditions employed in these studies. Consequently, approx. 95% of the reactive ronidazole metabolite(s) can react with other constituents in the reaction media such as other thiols or water. Based on these results, a mechanism is proposed for the metabolic activation of ronidazole.     

A numerical taxonomic study of species of Vibrio isolated from the aquatic environment and birds in Kent, England

A numerical taxonomic study has been carried out to confirm the identity of strains of the family Vibrionaceae isolated during an ecological study. A total of 237 strains were studied including 148 from the aquatic environment, 6 from estuarine birds, 1 from sheep faeces, and 61 control cultures. Duplicates of 21 of the strains were randomly selected and included to estimate test and operator error. Taxonomic resemblance was estimated on the basis of 148 characters using Euclidean distance. The taxonomic position of some strains was reevaluated using the pattern difference coefficient. Strains were clustered by three methods, all of which gave similar results. The estimated average probability of test error was 1.5%. Strains previously identified as Vibrio anguillarum fell into four distinct phenons corresponding to V. anguillarum biovar I, ' V. anguillarum biovar II', V. diazotrophicus , and strains pathogenic to oyster larvae. The latter group characteristically degraded xanthine and probably represents a new species. The phenon corresponding to V. cholerae included the type strain, strains of human origin, and strains isolated in the United Kingdom from birds and the aquatic environment. Some strains of V. cholerae were luminous. Other phenons were identified as V. metschnikovii, V. fluvialis , and Aeromonas spp.     

Characterization of a cytosolic fucosylation pathway in Dictyostelium.

FP21 is a 21-kDa fucoprotein which fractionates with the cytosol after high-speed centrifugation of gently lysed Dictyostelium cells. Less than 0.7% of FP21 is associated with vesicles. In proliferating cells, 4 x 10(5) fucosyl moieties/cell are associated with FP21 as anionic, possibly O-linked oligosaccharides equal in size to 4.8 glucose units. FP21 is underfucosylated in a mutant strain (HL250) that depends on extracellular fucose for synthesis of GDP-fucose. To determine the cellular site of FP21 fucosylation, cytosolic and vesicular preparations from strain HL250 were compared for their ability to transfer fucose from GDP-fucose to FP21. Cytosolic preparations fucosylate endogenous FP21 in a time-, concentration-, and divalent cation-dependent fashion, with a Km for GDP-fucose of 1.4 microM. Activity in normal cell cytosol is dependent on exogenous mutant FP21, demonstrating that FP21 is normally fully fucosylated. Both mutant and normal cytosols are also able to alpha-fucosylate a type 1 glycolipid substrate (8-methoxycarbonyloctyl-Gal beta 1-3 beta GlcNAc), but not related substrates, with Km values for the type 1 glycolipid of 0.99 mM and for GDP-fucose of 1.6 microM. Competitive inhibition between FP21 and the type 1 glycolipid shows that the same enzyme fucosylates both substrates. Intact and permeabilized vesicle preparations from wild-type cells are unable to fucosylate FP21 or the type 1 glycolipid by a divalent cation-dependent mechanism, and thus are devoid of FP21-fucosyltransferase. Since control experiments showed that vesicle leakage is minimal during cytosol preparation, these results indicate that FP21 is synthesized and fucosylated in the cytosolic compartment, by an unusual soluble fucosyltransferase.     

Germination and growth of cultivars ofTrifolium subterraneum L. in the presence of sodium chloride salinity

Summary Germination and growth responses of 15 early to midseason cultivars ofTrifolium subterraneum L. were determined at a range of irrigation water salinities (NaCl). There were significant cultivar differences in seed germination under standard conditions in the presence of pure solutions of NaCl from −10 to −330 kPa osmotic potential range. There were also significant cultivar differences in growth on a clay loam soil with increasing NaCl over the same range of osmotic potentials as used to test germination. There was a generally poor correlation between salt tolerance at germination and at later stages of growth.     

Prehistoric cultivated cucurbits from the Viru Valley,Peru

A sample of 535 specimens of cucurbits were retrieved from archaeological deposits in the Viru Valley, Peru, from contexts dated between ca. 1800 B.C.– 1100 A.D. by Carbon-14 analysis and cultural associations. Cultivars ofCucurbita maxima Duch. and C.moschata (Duch.) Duch. ex Poir. are found to be restricted, respectively, to early and late chronological periods, with no overlap. Cultural and ecological factors are suggested to account for the observed temporal and spatial variations in species occurrence. Comparison of materials from other coastal valleys indicat es significant, but presently unexplainable, spatial and temporal differences in the distribution of these species. Supportive evidence for South America as an independent center of domestication for C.maxima tis offered.     

Minireview possible roles of dietary fats in carcinogenesis

Epidemiological data have implicated dietary fat as an important factor in the aetiology of various cancers in humans. This suggestion is supported by the results of experiments with animals which have shown that increased amounts of dietary fat, in particular polyunsaturated fat, increase the incidence of some spontaneous and induced tumours. The enhancement of carcinogenesis by dietary fats appears to be exerted at the promotional stage of carcinogenesis. Changes induced by dietary fats in several biological systems involved in carcinogenesis may well indicate the underlying mechanisms responsible for the results of these experiments. These include the effects of dietary fats on the metabolism of chemical carcinogens, the structure and function of membranes, immunocompetence, DNA repair potential and endocrine function.     

Recruitment in networks of pulmonary capillaries.

To improve our understanding of the pressure-flow characteristics of pulmonary capillaries, we analyzed by means of computer stimulation a theoretical model composed of 50 interconnected nonlinear elements. Each element required a critical pressure across it before flow occurred and there was a subsequent linear pressure-flow region whose slope, or resistance, could be related to the transmural pressure of the element ("distensibility"). The critical pressures and resistances of each element of the network were randomly chosen from distributions. We found that recruitment (i.e., onset of flow) occurred over a large range of network upstream or "arterial" pressures, and that relatively high arterial pressures were required before all elements had no distensibility. Intermittent and reverse flow were commonly seen in some elements as the arterial pressure was raised in steps. These flow reversals were particularly common when the critical pressures and resistances of the elements were inversely related. The critical pressures required for such behavior in the capillary segments of the pulmonary microcirculation were calculated to be extremely small, of the order of 0.02 cmH2O. Pressures of this magnitude might result from sticking of red cells to capillary walls or to each other. The properties of such a network may explain the patchiness of flow in the pulmonary microcirculation and the large range of arterial pressures over which recruitment is observed to occur.