A unique mechanism for thiolation of serum albumins by disulphide molecules

Protein S-thiolation is a reversible oxidative modification that serves as an oxidative regulatory mechanism for certain enzymes and binding proteins with reactive cysteine residues. It is generally believed that the thiolation occurs at free sulphydryl group of cysteine residues. Meanwhile, despite the fact that disulphide linkages, serving structural and energetic roles in proteins, are stable and inert to oxidative modification, a recent study shows that the thiolation could also occur at protein disulphide linkages when human serum albumin (HSA) was treated with disulphide molecules, such as cystine and homocystine. A chain reaction mechanism has been proposed for the thiolation at disulphide linkages, in which free cysteine (Cys34) is involved in the reaction with disulphide molecules to form free thiols (cysteine or homocysteine) that further react with protein disulphide linkages to form the thiolated cysteine residues in the protein. This review focuses on the recent finding of this unique chain reaction mechanism of protein thiolation.

Protective effect of two synthetic compounds against chlorsulfuron injury in maize ( Zea mays L.)

Two new synthetic compounds — urea (B-3) and thiourea (B-6) derivatives of 4-methylpiperazinyl — were investigated as possible antidotes for chlorsulfuron in maize. It was established that the thiourea derivative was a more effective herbicide protector than the urea derivative. The shoot length of maize plants treated with 10 −5 M chlorsulfuron was inhibited 60% compared to the untreated plants, whereas pretreatment with 5×10 −4 M B-6 reduced this inhibition to 23%. Moreover, the decrease of 53% in shoot fresh weight caused by herbicide applied alone was countered almost completely by B-6 with only an 11% loss in fresh weight observed. The results of this investigation show that the urea derivative (B-3) appeared to be ineffective in antidoting the injurious effect of chlorsulfuron. Decreases in root length and fresh weight were also offset by B-6. The more favourable protective activity of the thioureido group in B-6 could be due to the formation of an isomer with isothiourea structure, having a sulphydryl group. Treatments with herbicide and B-3 / B-6 alone or in combination had no significant effect on the parameters of the antioxidative defence system tested.

Mineralization of [14C]octacosane by Acinetobacter calcoaceticus S30

Acinetobacter calcoaceticus S30 could grow (doubling time, 7 h) on octacosane (C28) and degraded about 70% of the substrate during growth. Octacosanol, octacosanoic acid, and other lower carboxylic acids were identified during degradation of octacosane. Acinetobacter calcoaceticus S30 could also grow on intermediate metabolites, namely octacosanol and octacosanoic acid, although the doubling time was greater on octacosanoic acid (72 h on octacosanol and 120 h on octacosanoic acid). Whole cells of A. calcoaceticus S30 using [18-14C]octacosane mineralized 65% of the octacosane to 14CO2 and 30% of the radiolabel was retained in the cell biomass in 24 h. Acinetobacter calcoaceticus S30 converts octacosane to octacosanol through an oxidation step, which is then oxidized to octacosanoic acid and then β-oxidized to CO2. Among several metabolic inhibitors, those of the sulphydryl group greatly inhibited the uptake of octacosanol and octacosanoic acid at much lower concentrations. The electron transport inhibitors were potent inhibitors of octacosane, octacosanol, and octacosanoic acid uptake, suggesting that the oxidation of these substrates is an energy-dependent process.Key words: Acinetobacter calcoaceticus, mineralization, octacosane, octacosanol, octacosanoic acid.