Oxidized thioredoxin undergoes sulfitolysis of its single disuifide bond at low concentrations of sultlte ions and protein and in the absence of denaturing agents. The reaction, which has an optimum at pH 8, was studied using ~%]sultite and E. coii thior~o~n as model. The product, t~or~o~n-~-sulfonate, has a half-life of several hours in solution. It is unable to activate chloroplast NADP malate dehydrogenase. Thioredoxin suhitolysis may therefore be a physiologically important factor in mediating the phytotoxic effects of sulfur dioxide in plants.

Testing the IgM and IgA immune response to polysaccharide vaccination with a multivalent PnPS ELISA may be a feasible tool for assessment of the immune function in patient groups who receive IgG replacement therapy.

Thioredoxins and glutaredoxins, in their oxidized form, possess a single disulfide bridge located on an edge of the small compact molecules. In contrast to most other disulfide-containing proteins, this S-S bridge is cleaved by millimolar concentrations of sulfite in the absence of protein denaturing agents at pH 7-8 and ambient temperature; however, the reaction is not quantitative. Sulfitolysis of Escherichia coli thioredoxin was found to be associated .with an increase in fluorescence at 345 nm. A comparative study of sulfitolysis in 12 different thioredoxins and glutaredoxins of bacterial and plant origin has been made. Although they are all thought to be highly conserved in threedimensional structure, their reactivities towards sulfite and the effects of 6 M guanidinium chloride (not affecting, or enhancing sulfitolysis) vary strongly in the series, with E. coli thioredoxin being less reactive and plant thioredoxins and E. coli glutaredoxin being more susceptible molecules. Contrary to expectation, reaction with sulfite is not generally correlated with the presence of negatively or positively charged amino acid residues near the disulfide loop but is determined by individ-

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