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PubMed1989

Preservation of sodium-dependent iodide transport activity by methimazole and mercaptoethanol in phospholipid vesicles containing thyroid plasma membranes: with evidence of difference in the action of perchlorate and thiocyanate.

The effect of methimazole (MMI) and 2-mercaptoethanol (ME) on I-transport was studied using phospholipid vesicles (P-vesicles) made from porcine thyroid plasma membranes and soybean phospholipids by sonication. 1. When buffer solutions contained either 1 mM MMI or 2 mM ME, I-uptake by P-vesicles in the presence of external Na+ was apparently higher than that in the absence of external Na+. Na+-dependent I- uptake was inhibited by both C1O4- and SCN- added externally. 2. When PM was treated with 4 mM N-ethylmaleimide prior to preparation of P-vesicles, the activity of Na+-dependent I- transport was completely lost even when P-vesicles were incubated in the presence of ME. 3. When neither MMI nor ME was added to buffers, I- uptake in the presence of external Na+ was not at all higher than that in the absence of external Na+. In these instances, however, I- uptake was much higher compared than the baseline uptake in the presence of MMI or ME, and was inhibited by external SCN- and not by C1O4- without relation to external Na+. These data indicate that MMI or ME has two distinct effects on our model system of I- transport. The one is preservation of the Na+-dependent I- transport activity by protecting a sulfhydryl group, and the other is reduction of nonspecific I- binding to P-vesicles. In addition, C1O4- is a more specific inhibitor of thyroid I- transport than SCN-, when non-specific I- oxidation is imperfectly prevented.

Animals↗
PubMed1990

On the mechanism of hydrogen peroxide formation during precipitation of hemoglobin with perchloric acid.

During acid precipitation of hemoglobin, hydrogen peroxide is formed. The oxidant is generated from hemoglobin-bound as well as from physically dissolved oxygen, provided divalent hemoglobin-iron is present. The extent of hydrogen peroxide formation seems to be dependent on the precipitating reagent. From experiments on GSH oxidation during precipitation of red cells and from a literature survey formation of at least one second reactive oxygen species has to be assumed. Different reaction pathways for generating these oxidants during acid precipitation are discussed: Hydroperoxide which is probably liberated by proton catalysis may contribute to the observed oxidation reactions. At pH approximately 1 it rapidly disproportionates yielding oxygen and hydrogen peroxide, which might produce reactive oxidants with hemoglobin intermediates formed during precipitation. In addition a new hypothesis is presented explaining the ability of N-ethylmaleimide to inhibit GSH oxidation during precipitation of red cells. Accordingly, the SH-reagent rapidly penetrates the cell membrane and reacts with GSH before access of protons prevents alkylation.

Chemical Precipitation↗