Solubilization of lymphocyte and thymocyte antigens by a reversible chemical modification

Effects of temperature and pH on the regeneration of the amino groups of ovalbumin after modification with citraconic and dimethylmaleic anhydrides

The reagents citraconic and dimethylmaleic anhydrides modify the amino groups of proteins in a reversible way, the modified amino groups being regenerated at moderate acid pH. To use these reagents efficiently it is important to know the stabilities of the modifed groups under different experimental conditions. We have studied the kinetics of deacylation of ovalbumin amino groups modified with citraconic and dimethylmaleic anhydrides, under different conditions of temperature (0-40 degrees C) and pH (4-8). The deacylation of the modified groups follows pseudo-first-order kinetics under all experimental conditions studied. For both reagents, the dependence of the rate of deacylation on temperature obeys the Arrhenius equation, and the logarithm of the apparent deacylation constant shows a linear dependence on pH. From the experimental data, equations have been obtained for both reagents relating the deacylation constant with temperature and pH. These equations allow the calculation of the deacylation constant and the half-life of the modified groups for any conditions of temperature and pH within the experimental intervals studied.

Heterogeneity of human cell membrane sialoglycoproteins

Discontinuous sodium dodecysulfate polyacrylamide gel electrophoresis (disc SDS-PAGE) followed by periodic acid/Schiff staining reveals the presence of six sialoglycoprotein bands in human red cell membranes or glycoprotein preparations therefrom. In agreement with previous investigations it is shown that PAS-1 and PAS-2 (mol. weight 37 000) are different forms of the same molecule (MN glycoprotein). Using separation of glycoproteins by the system of Weber and Osborn and reelectrophoresis of gel slices by disc SDS-PAGE it is demonstrated that the minor component C (mol. weight 41 000) represents the dimeric form of PAS-3 (Ss glycoprotein). Band B corresponds to an aggregate of PAS-3 and PAS-2 and/or the trimer of PAS-3 with possible differences between extracted glycoproteins and those present in the membrane. The minor component D (mol. weight 35 000) is, as far as could be elucidated, not involved in aggregation phenomena. Some technical problems of glycoprotein fractionation by SDS-PAGE and the remarkable effect of phosphate buffers on the glycoprotein pattern are discussed.

Studies on the receptors of the MNSs group system

Results with modified human red cell membrane sialoglycoproteins indicate that alkali-labile sialic acid and amino groups are parts of the erythrocyte receptor sites recognized by common rabbit and human anti-M and -N sera. The "N" antigen, demonstrable in MM glycoprotein preparations by rabbit anti-N, has structural properties which are similar to those of the MN receptors. Sialic acid, amino groups and carbohydrate, susceptible to periodate oxidation, are not involved in the Ss antigen sites. The specificity of the Vicia graminea lectin is dependent on free amino and carboxyl groups. Its affinity for the substances is increased by blocking of amino groups.

Proteins selectively released from water-extracted human erythrocyte membranes upon citraconylation or maleylation. Electrophoretic analysis and chromatographic fractionation

1. Citraconylation or maleylation (carboxylation) of water-extracted human erythrocyte membranes (membrane residue) solubilized up to 20% (w/w) of the membrane residue protein, but less than 2% of the phospholipids. Amino acid analysis and polyacrylamide gel electrophoresis in the presence of dodecylsulfate showed that the solubilization was selective. 2. Polyacrylamide gel electrophoresis in the absence of detergent separated the solubilized acylated proteins into four well-separated major zones and two or three minor zones. Two of the major zones contained proteins of high molecular weight (spectrin components) and the other two contained components of intermediate molecular weight. 3. The solubilized components of intermediate molecular weight could be partially purified by hydroxyapatite chromatography. 4. Upon incubation at pH 5 and 36 degrees C of the unfractionated proteins solubilized by citraconylation some components became specifically degraded or dissociated into subunits.