Cobalt transport in nickel-resistant strains ofNeurospora crassa

Uptake of Co²⁺ by three nickel-resistant strains (Ni^R1, Ni^R2, and Ni^R3) ofNeurospora crassa that differed in resistance to Co²⁺ has been studied. Uptake was linear with Co²⁺ concentration (up to 1 mM), with time (up to 6 h), and with pH between 3 and 6. Uptake rates were in the order Ni^R2>Ni^R1>Ni^R3. In all strains, there was gradual increase in Co²⁺ uptake between 10° and 28°C, with a much sharper increase between 28° and 40°C. Metabolic inhibitors decreased Co²⁺ uptake partially in all strains, except for KF in Ni^R3. About 50–80 g Co²⁺/100 mg dry weight was surface bound. Ni²⁺, Zn²⁺, and Mn²⁺ competed with Co²⁺, the effects being strain specific. Mg²⁺ inhibited Co²⁺ uptake in all strains with preformed mycelia. In Ni^R1 and Ni^R2 only with young mycelia (40 h old) was Mg²⁺ inhibitory to Co²⁺ uptake,during growth in the presence of Co²⁺. The results suggested the presence of two transport systems for Co²⁺ in Ni^R1 and Ni^R2, only one of which was sensitive to Mg²⁺; in contrast, Ni^R3 had a single system, which was sensitive to Mg²⁺.     

Induction of male flowers in a pistillate line ofRicinus communis L. by silver and cobalt ions

Aqueous solutions of silver nitrate (10–100 g/plant) and cobalt chloride (125–500 g/plant), injected into the main stem of plants of the pistillate cv. 240 ofRicinus communis when the vegetative shoot apex was beginning to become reproductive, induced the formation of staminate (male) flowers with viable pollen in the normally strictly pistillate (female) terminal inflorescence, their number increasing with the dose of Ag⁺ and Co²⁺. No formation of bisexual flowers was noted. Female flowers pollinated with pollen from the induced male ones produced fruits and viable seeds.     

Hepatic and extra-hepatic glutathione-S-transferase activity in wild pigeons (Columba livia)

Glutathione-S-transferase (EC 2.5.1.18) activity was assayed in hepatic and extra-hepatic tissues of pigeons using l-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene as substrates. Gluthathione-S-transferase activity towards 1-chloro-2,4-dinitrobenzene in pigeon was in the order: kidney > liver > testes > brain > lung> heart. The enzyme activity with 1-chloro-2,4-dinitrobenzene as substrate was 40–44 times higher in pigeon liver and kidney than that observed with 1,2-dichloro-4-dinitrobenzene as substrate.K _m values of hepatic and renal glutathione transferase with l-chloro-2,4-dinitrobenzene as substrate were 2.5 and 3 mM respectively. Double reciprocal plots with varying reduced gluthathione concentrations resulted in biphasic curves with twoK _m values (liver 0.31 mM and 4mM; kidney 0.36 mM and 1.3 mM). The enzyme activity was inhibited by oxidized gluthathione in a dose-dependent pattern. 3-Methylcholanthrene elicited about 50% induction of hepatic glutathione transferase activity whereas phénobarbital was ineffective.     

A general multistate model for the analysis of hydrogen-exchange kinetics

In proton nmr, the chemical exchange rates of slowly exchanging labile hydrogens (with lifetimes in the range ～ 10 msec – ～ 1 sec) of peptides, proteins, and nucleic acids can be measured in H₂O by a combination of two separate experiments: (1) the transfer of solvent saturation and (2) saturation-recovery experiments. When these molecules exist in a dynamic equilibrium among different conformations, the experiments cannot be analyzed in a straightforward manner to derive the intrinsic exchange rates. In the present study we have derived analytical expressions for the above two experiments on a biomolecule under certain limiting conditions: (1) the extreme low-motility limit, where each of the conformational transitions is much slower than the corresponding hydrogen exchange rate with the solvent; (2) the high-motility limit (EX₂ mechanism), which is the opposite extreme of the previous limit; and (3) the low-motility limit (EX₁ mechanism), which is a mixture of limits (1) and (2), i.e., for some of the conformations, the exchange rate with the solvent is much faster than their conformational transition rates, while for the remaining conformations the reverse situation is realized. The results may be considered as a generalization to an arbitrary number of states of the two-state model treated by Hvidt. Equations have also been derived that are applicable to the iostope exchange method of measuring very slow exchange rates (with life-times of the order of minutes and longer) in biomolecules. The saturation recovery experiments performed in H₂O on the active pentapeptide fragment of thymopoietin serve to illustrate the high-motility limit. The theoretical formulation presented in this study can be easily adapted to other double-resonance techniques and also to situations where the kinetics of an arbitrary system existing in a multistate equilibrium are of interest.     

The amino acid sequence of ferredoxin from the alga Mastigocladuslaminosus

Ferredoxin was purified from the thermophilic blue-green alga, Mastigocladuslaminosus. The physicochemical properties of this ferredoxin are similar to those of other [2Fe-2S] plant ferredoxins except for its unusual thermal stability. The primary structure of the protein was determined and consists of 98 amino acid residues, 5 of which are cysteines. The positions of 4 cysteines which bind the iron atoms of the active centre are identical to those in other ferredoxins. The primary structure of the ferredoxin does not reveal any special features to account for its high thermal stability.     

Hydroxylamine inhibition of the nitrate reductase complex from Amaranthus

Nitrate reductase from Amaranthus viridis is similar to nitrate reductase from other plant sources. NH₂OH inhibits nitrate reduction from NADH by the nitrate reductase complex, but it does not inhibit either the NADH-dehydrogenase activity or nitrate reduction from reduced flavin mononucleotides. The inhibition observed was non-competitive with nitrate when the enzyme was pre-incubated with NH₂OH and NADH, and competitive with nitrate without pre-incubation. The K_i values for NH₂OH were 5 μM and 30 μM with or without pre-incubation respectively.     

Cross-neutralization reactions of Escherichia coli and Vibrio cholerae enterotoxins as studied by rabbit skin inoculation test.

Neutralization of enterotoxins of Vibrio cholerae 569 B and Escherichia coli 10407 by antitoxins to V. cholerae 569 B, E. coli 334, 408-3 and 10407 was studies by intradermal inoculation test in the rabbit. Neutralization of V. cholerae enterotoxin by homologous as well as heterologous antisera of E. coli was observed, except that there was no neutralization of the enterotoxin by antiserum to E. coli 408-3 enterotoxin. Neutralization of E. coli enterotoxin to a varied extent by homologous as well as all heterologous antisera, including that of V. cholerae 569 B antitoxin, was also observed.     

Studies on copper toxicity in nickel-resistant strains ofNeurospora crassa

Copper toxicity has been studied in three nickel-resistant strains ofNeurospora crassa (Ni^R1, Ni^R2, and Ni^R3). Ni^R1 and Ni^R2, but not Ni^R3, were two-to threefold more sensitive than the parent wild strain (N. crassa EM 5297a) to Cu²⁺ on a normal N medium. On a nitrate N medium, Cu²⁺ was 16-fold more toxic to Ni^R3 because of reduced synthesis of nitrite reductase; Ni^R1 and Ni^R2 were only fivefold more sensitive to Cu²⁺, and nitrite reductase synthesis was unaffected. Mn²⁺ reversed Cu²⁺ toxicity on normal N medium only, in all strains. Fe³⁺ counteracted Cu²⁺ toxicity on nitrate N medium also. It was shown that Cu²⁺ affected Fe³⁺ utilization for nitrite reductase synthesis in Ni^R3 only and that in these Ni²⁺-resistant strains, Fe³⁺ antagonized effects of Cu²⁺, but not of other toxic metal ions.     

NMR studies of the variant-3 neurotoxin from Centruroides sculpturatus Ewing

We report a preliminary high-resolution proton nuclear magnetic resonance characterization of the variant-3 toxin from the scorpion Centruroides sculpturatus Ewing (range Southwestern USA). This toxin assumes a well defined folded conformation in aqueous solutions at room temperature and undergoes reversible thermal denaturation. A number of amide hydrogens exhibit exchange life times varying from several minutes to several hours. A few tentative assignments of the low field aromatic CH resonances has been made on the basis of 2D-COSY and NOE experiments. The upfield shifts exhibited by Trp-47 suggest a unique microenvironment for this residue. The NMR data suggest that there is some degree of correlation between the solution structure of the variant-3 toxin and its crystallographic structure. Our studies provide a basis for a detailed elucidation of the structure-function relationships of these interesting scorpion toxins which bind to the sodium channels of excitable membranes and delay sodium current inactivation.     

Effects of cadmium salt on phosphomonoesterases activity and fertilizing ability of fowl spermatozoa.

Daily administration of cadmium salt for 25 days (2.5 mg per Kg body weight) in the male domestic fowl caused the end of treatment period. An increased incidences of concentration. Fertility dropped to zero at the end of the treatment period. Activity of acid and alkaline phosphomonoesterases were also drastically reduced by the end of treatment period. An increased incidences of morphological abnormalities of spermatozoa were noticed in the treated birds. After 46 days cessation of the treatment, full recovery of the above measures was found. These alterations suggest the reversible type of effect of cadmium chloride on the spermatozoa of male domestic fowl.