Modification by simetryn sulphoxide of a specific thiol group in rat haemoglobin.

Native rat haemoglobins were found to bind simetryn sulphoxide to an extent 40-fold greater than human haemoglobin. This specific behaviour was studied by using only high-pressure ('performance') liquid chromatography for the preparative separation of globin chains and the isolation of peptides resulting from chemical and enzymic degradation. High recoveries (greater than 80%) of peptides throughout the procedures in combination with microsequence techniques, allow a definitive assignment of the residue undergoing modification. The haemoglobin beta-chain cystine-125 residue, with a stoichiometry of one per tetramer of rat haemoglobin, was found to be modified. Stereochemical implications of this finding are discussed. Simetryn sulphoxide would appear to be useful as a specific reagent for the mapping of exposed thiol residues in proteins.     

Cyclosporin A regulates the expression of HLA-DR on human monocytes by two different mechanisms.

Cyclosporin A (CsA), but not its nonimmunosuppressive analog cyclosporin H (CsH), inhibited the expression of HLA-DR in human monocytes. Induction of HLA-DR by interferon (IFN)-gamma in fresh monocytes was also inhibited by CsA and not by CsH. However, when monocytes were pretreated with either CsA or CsH for 16 hr prior to the addition of IFN-gamma, HLA-DR expression was increased, probably because of a cyclosporin-induced increase in the number of IFN-gamma receptors. Down-regulation of the HLA-DR mRNA by CsA was found to be dependent on continuous protein synthesis. IFN-alpha also inhibited the IFN-gamma-induced HLA-DR mRNA expression and showed synergy with CsA at low concentrations but not at high concentrations of the drugs. A common mechanistic element in the pathways of CsA and IFN-alpha is proposed.     

Plant-induced changes in the redox potentials of rice rhizospheres

Redox potentials in microsites of the rhizosphere of flooded rice were continuously measured for several days. Close to the root tips redox potential markedly increased. The highest increase was measured in the rhizosphere of the tips of short lateral roots. Aerobic redox conditions were reached there, except in a very strongly reduced soil. Both the extension of the oxidation zone around the root tips and the maximum redox potential reached were influenced by the reducing capacity of the soil. The radius of the redox rhizosphere varied from less than 1 mm in a strongly reduced soil up to 4 mm in a weakly reduced one. The root-induced oxidation processes in the rhizosphere depended on the atmospheric oxygen supply to the roots.     

Influence of sulphur dioxide on the fermentation of sulphite spent liquor

In fodder yeast production from sulphite spent liquor, sulphur dioxide is well-known as a yeast poison. The present paper deals with the detailed influence of sulphur dioxide. The experimental work was done in a laboratory fermenter under technical conditions. A decrease in biomass yield, and an increase in oxygen consumption, caused by increasing carbon dioxide production, were found. During the fermentation, there is no destruction of the carbonyl-bisulphite adduct to be observed. Sulphur dioxide has no influence on the crude protein content of yeast cells, and there is also no influence on the morphology of cells.     

Ferredoxin-dependent methane formation from acetate in cell extracts of Methanosarcina barkeri (strain MS).

Cell extracts of Methanosarcina barkeri grown on acetate catalyzed the conversion of acetyl-CoA to CO2 and CH4 at a specific rate of 50 nmol min-1 mg-1. When ferredoxin was removed from the extracts by DEAE-Sephacel anion exchange chromatography, the extracts were inactive but full activity was restored upon addition of purified ferredoxin from M. barkeri or from Clostridium pasteurianum. The apparent Km for ferredoxin from M. barkeri was determined to be 2.5 M. A ferredoxin dependence was also found for the formation of CO2, H2 and methylcoenzyme M from acetyl-CoA, when methane formation was inhibited by bromoethanesulfonate. Reduction of methyl-coenzyme M with H2 did not require ferredoxin. These and other data indicate that ferredoxin is involved as electron carrier in methanogenesis from acetate. Methanogenesis from acetyl-CoA in cell extracts was not dependent on the membrane fraction, which contains the cytochromes.