IgG autoantibodies in human serum selectively bind to a glycopeptide antigen that appears on senescent and damaged cells in situ. We identified the membrane protein from which the senescent cell antigen is derived by using a phagocytosis-inhibition assay and immunoautoradiographic gel staining and electroblotting techniques. Results of the phagocytosis-inhibition assay revealed that only the purified transmembrane glycoprotein designated "band 3" and senescent cell antigen inhibited the phagocytosis of erythrocytes induced by IgG eluted from senescent erythrocytes. Purified spectrin, syndein, band 4.1, actin, glycophorin A, and intact or desialylated sialoglycoprotein periodic acid/Schiff (PAS) staining bands 1-4 containing glycophorins A, B, and C did not inhibit phagocytosis. Specific antibodies against the senescent cell antigen and erythrocyte band 3 were used to identify the membrane protein from which the senescent cell antigen is derived. Band 3-related polypeptides (Mrs 60,000,42,000, and 18-26,000) were identified in erythrocyte ghosts prepared in the presence of diisopropyl fluorophosphate, phenylmethylsulfonyl fluoride, and EDTA by immunoautoradiography with antiband 3. Antibodies to senescent cell antigen reacted with band 3 and the same lower Mr band 3-related polypeptides. Thus, the senescent cell antigen is immunologically related to band 3. oglycoprotein mixtures through it, a procedure that depleted

Mono-, di-, and trisulfonic acids, including 4,4'-diacetamido stilbene-2,2'-disulfonic acid (DAS) and 2-(4'-amino phenyl)-6-methylbenzene thiazol-3',7-disulfonic acid (APMB) produce a reversible inhibition of sulfate equilibrium exchange in human red cells. A study of the sidedness of the action of a number of these sulfonic acids in red cell ghosts revealed that some, like DAS, inhibit only at the outer membrane surface while others, like APMB, inhibit at either surface. This finding suggests that at least two different types of membrane sites are involved in the control of anion permeability. The nature of the anion permeability controlling sites in the outer cell surface was investigated by studying the effects of DAS on the inhibition by dinitrofluorobenzene (DNFB) of anion equilibrium exchange and on the binding of DNFB to the proteins of the red blood cell membrane. After exposure to DNFB in the presence of DAS for a certain period of time, there was a reduction of both the inhibitory effect of DNFB on sulfate exchange and the binding of DNFB to the protein in band 3 of SDS polyacrylamide gel electropherograms (nomenclature of Steck, J. Cell. Biol., 62: 1, '74). Since binding to other membrane proteins was not affected, this observation supports the assumption that the protein in band 3 plays some role in anion transport. In accordance with the absence of an inhibitory effect at the inner membrane surface, internal DAS does not affect DNFB binding to the protein in band 3. DAS protected the anion exchange system not only against inhibition by DNFB but also by m-isothiocyanato benzene sulfonic acid. In contrast to DAS, the equally inhibitory phlorizin does not reduce the rate of dinitrophenylation of the protein in band 3. This suggests that either not all inhibitors of anion exchange exert their action by a combination with sites on the protein in band 3 or that in spite of the described evidence this protein is not involved in the control of anion movements.

Measuring the rate of dinitrophenylation of a specific lysine residue (called a) that is allosterically linked to the transfer site, it could be demonstrated that the anion transport protein may exist in two different conformational states, designated cis and trans. In the cis conformation a is easily accessible for reaction with dinitrofluorobenzene; in the trans conformation, a is less accessible. In the presence of the substrate anion Cl, the equilibrium between the cis and trans conformation is towards the cis conformation. Reversibly acting inhibitors of anion transport arrest the transport system, either predominantly in the cis or in the trans conformation. Phlorizin and certain positively charged derivatives of furosemide produce arrest in cis conformation, internal 2-(4'-aminophenyl)-6-methylbenzenethiazol-3',7-disulfonate (APMB) and Ca++ in trans conformation. Within this frame of reference, the different susceptibilities of the transfer site to internal and external 4,4' diacetamido-2,2'-stilbene disulfonate (DAS) are interpreted on the assumption that the conformation of the transfer site changes during the transition of the transport protein from the cis to the trans conformation, so that in the trans conformation a reaction with DAS is no longer possible.

Soil salinity is one of the most severe factors limiting growth and physiological response in cowpea plants. In this study, the possible role of γ-irradiation in alleviating soil salinity stress during plant growth was investigated. Increasing salinity in the soil (25, 50, 100 and 200 mM NaCl) decreased plant growth, photosynthetic pigments content, total carbohydrate content and mineral uptake compared to control, while increased total phenol content, proline, total free amino acids and lipid peroxidation. Seed irradiation with gamma rays significantly increased plant growth, photosynthetic pigments, total carbohydrate, total phenol, proline, total free amino acids and the contents of N, P, K +, Ca+2 and Mg+2 compared to non irradiated ones under salinity. On the other hand, irradiation with gamma rays decreased lipid peroxidation, Na+ and Cl- contents which may contribute in part to activate processes involved in the alleviation of the harmful effect of salt at all concentrations used (25, 50 and 100 mM) except at the high concentration (200 mM). Electrophoretic studies of α-esterase, β-esterase, polyphenol oxidase, peroxidase and acid phosphatase isozymes showed wide variations in their intensities among all treatments.

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