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Additional protein fraction migrating slower than spectrin has been detected in erythrocyte membranes from an ataxia-telangiectasia (A-T) patient and from his mother (A-T heterozygote). In erythrocyte membranes labelled with maleimide spin label changes in signal of the weakly immobilized spin label as related to that of strongly immobilized one (w/s) were noted. In comparison to age-matched control groups the values of w/s were lower in A-T heterozygotes (ten persons) and higher in A-T homozygotes (four persons). In control persons the values of w/s increased with age, whereas in families with A-T no significant differences in this parameter were noted between children and parents. The presence of additional protein fraction in erythrocytes membranes of A-T patient and A-T heterozygote indicates that these phenotypes can be differentiated from the healthy control persons for the first time on the basis of changes detected in the erythrocytes. This change in erythrocyte membrane may explain the decrease in the w/s parameter of electron spin resonance in A-T heterozygotes. On the other hand increased values of w/s in A-T patients may be caused by disease process.

Beta1-Fetoprotein (Fbeta1) and fetal hemoglobin (HbF) were compared with the help of immunodiffusion methods. They were shown to be non-identical although Fbeta1, as well as HbF, is stained by benzidine. Antisera against Fbeta1 do not form the line of precipitation with HbF. Besides, we succeeded to differentiate Fbeta1 from Fbeta2 (they are separated under chromatography on sephadex G-200). Fbeta1 differs from Fbeta2 by benzidine staining: Fbeta1 is benzidine-positive and Fbeta2 is benzidine-negative. The constant parallelism in the appearance of Fbeta2 and a monomeric subunit IgMs of the immunoglobulin molecule IgM. Both the proteins, Fbeta1 and Fbeta2, are present in the serum of a newborn, as well as of a patient with ataxia-teleangiectasia. At the same time erythrocytes of the latter do not contain HbF, as was shown by electrophoresis in polyacrylamide gel.

In a number of lymphoblastoid cell lines from individuals with the genetic disease ataxia-telangiectasia (A-T), a decrease in the levels of actin and a concomitant increase in the levels of a protein species of 37K has been observed to occur following high cell density. In this paper we describe ataxia-telangiectasia lymphoblastoid lines that show this response constitutively, and demonstrate that this 37K protein is most likely an actin-derived peptide. This is because of extensive similarity between the two proteins in the spectrum of peptides produced by proteolytic fingerprinting. It appears likely that this 37K protein is similar to the well documented protease-resistant actin fragments produced by protease digestion of actin in vitro. Examination of a number of possible initiators found no clear signal that promoted this response, although the response is clearly very dependent on cell culture conditions. The possible involvement of a cytoskeletal anomaly in ataxia-telangiectasia is discussed.