Effect of sodium dodecyl sulphate on the high molecular weight protein fraction of mustard (Brassica juncea) and rapeseed (Brassica campestris)

The effect of sodium dodecyl sulphate on mustard and rapeseed 12S protein has been monitored by the techniques of ultracentrifugation, viscosity, difference spectra and fluorescence spectrophotometry. At low concentration of sodium dodecyl sulphate (<3.47 mM) mustard protein undergoes aggregation and at higher concentrations it dissociates to 1.8 S protein, the dissociation being complete at 17.3 mM sodium dodecyl sulphate. The rapeseed protein, on the other hand, undergoes dissociation at all the concentrations of sodium dodecyl sulphate. The reduced viscosity values of mustard protein in the presence of the denaturant are higher than those of rapeseed protein. Similarly in difference spectra change in absorbance values of mustard protein are higher.’ The relative fluorescence intensity of the mustard protein increases with sodium dodecyl sulphate concentration, upto 0.87 mM and this is followed by fluorescence quneching at higher denaturant concentrations. However, with the rapeseed protein fluorescence quenching was observed at all concentrations of sodium dodecyl sulphate.     

Zinc-induced self-assembly of goat brain tubulin: some novel aspects

Unlike normal microtubule assembly, the $\text{in vitro}$ assembly of DEAE-purified goat brain tubulin in presence of Zn(II) is not inhibited by suprastoichiometric concentrations of antimicrotubular drugs like colchicine and podophyllotoxin. However, assembly in the presence of Zn(II) is inhibited by vinblastine. Vinblastine sensitivity of the assembly process depends on the Mg(II) concentration in the assembly medium. Like normal microtubules, Zn(II)-induced polymers are sensitive to cold. The polymers assembled in presence of Zn(II) are readily disassembled on treatment with Zn(II)-chelators like EDTA or o-phenanthroline, indicating that the binding of Zn(II) to tubulin is essential for maintaining the polymeric structure.     

Approaches to the measurement of intracellular adenine and the discrimination between adenine transport and metabolism in L1210 leukemia cells

Incubation of L1210 leukemia cells with 10 μM [³H]adenine in the absence of energy substrate results in a very rapid accumulation of ³H within the cells. By 20 s intracellular adenine is near steady-state; beyond this the rate of accumulation of intracellular ³H reflects nucleotide synthesis, predominantly the rate of ATP accumulation within the cell as determined by liquid chromatography. Adenine incorporation into the nucleotides proceeds via adenine-phosphoribosyl transferase, which is rate-limiting to AMP formation and subsequently the formation of ADP and ATP. Acceleration of this pathway by the addition of glucose and phosphate decreases the intracellular adenine level far below equilibrium as metabolism is increased relative to transport. Assessment of methodology to evaluate intracellular adenine and its metabolites indicates that (i) a 4°C wash removes the major portion of intracellular adenine and (ii) at 4°C, transport of adenine remains rapid and while nucleotide synthesis is decreased, ATP still accumulates within the cell. Hence, measurement of cellular uptake of radioactive label at 4°C after cells are washed free of adenine cannot be used as a measurement of adenine surface binding since this radioactive label represents, at least in part, phosphorylated derivatives of adenine within the cell. Unlabeled adenine and structurally related compounds were found to inhibit [³H]adenine net uptake under conditions where metabolism of adenine was reduced, suggesting that base transport is mediated by a facilitated diffusion mechanism. This is consistent with other studies from this laboratory that demonstrate exchange diffusion between adenine and other bases.     

Direct demonstration of electron transfer between tryptophan and tyrosine in proteins

With several proteins it has been shown that electrons can be transferred intramolecularly from tyrosine to electron-deficient tryptophan units. Rates vary from ～ 10²s^?1 (in lysozyme) to ～ 2×10⁴ s^?1 (in trypsin). For β-lactoglobulin the activation energy is 45kJ mol^?1. This is incompatible with charge conduction along the polypeptide chain and rules out any mechanism involving temperature-labile hydrogen bonds as the main pathway. It seems likely that the electron transfer proceeds directly between the aromatic groups, while they are maintained at a distance from each other.     

Influence of cathodic protection of mild steel on the growth of sulphate‐reducing bacteria at 35°C in marine sediments

In order to protect metallic structures from marine corrosion, cathodic protection using sacrificial anodes or impressed current is widely used. In aerated seawater steel is considered to be protected when a cathodic potential of — 800 mV/SCE (Saturated Calomel Electrode) is applied. However, in many cases, this potential must be lowered due to the presence and activity of microorganisms such as acid‐producing bacteria or sulphate‐reducing bacteria (SRB). SRB are obligate anaerobes using sulphate as an electron acceptor with resultant production of sulfides. Some SRB are able to use hydrogen as an electron donor causing thereby depolarization of steel surfaces.

An experiment was performed in marine sediments to determine the relationship between cathodically produced hydrogen and growth of SRB in marine sediments both at ambiant temperature (Therene, 1988) and at 35°C. Results concerning the latter experiments are reported here.

Analytical techniques included microbiological analyses, lipid biomarker studies and electrochemical measurements including AC impedance spectroscopy. Results indicated a change in the bacterial community structure both on the steel and sediment as a function of time and potential. The results also showed that cathodically‐produced hydrogen promoted the growth of SRB with the Desulfovibrio genus predominating.