Band 4.1-like Proteins of the Bovine Lens. Effects of Differentiation, Distribution and Extraction Characteristics

Bovine lens epithelium, cortex and nucleus were screened for the presence of red-cell-membrane band 4.1-like proteins by using an immunoblot method. Lens epithelial cells were found to contain proteins of Mr 78 000 and higher (approximately 150 000) that cross-reacted with anti-(protein 4.1) sera. Fibre cells of the superficial cortex were also found to contain these two proteins, as well as an additional protein of approx. 80 000 Mr. In contrast, deep layers of the cortex and the lens nucleus contained no detectable cross-reactive protein at these Mr values. Treatment of a crude membrane fraction prepared from superficial bovine cortices with a low-ionic-strength buffer resulted in release of the high-Mr band 4.1-like protein. The 80 000- and 78 000-Mr proteins remained with the membrane fraction in low-ionic-strength buffer, but were released into solution by high-ionic-strength-buffer treatment. We have also demonstrated that the human red-blood-cell membrane, like lens epithelial cells and fibre cells, also contains a high-Mr band 4.1-like protein that is released from membranes by low-ionic-strength-buffer treatment.