The amino acid composition of 350 lymphocyte proteins

We determined the amino acid composition of proteins of Sp2 hybridoma cells by a procedure which assembles the information on the polypeptides upon two-dimensional gel electro-phoresis, such that biosynthetic labeling with 20 different ³H amino acids provides the data-spot intensities-on the relative representation of the detected polypeptides. The gels were impregnated with 2,5-diphenyloxazol (PPO) and suitably exposed radiofluorographs were selected for analysis. The images originating from the 12 cultures labeled with amino acids R, A, H, I, L, K, M, F, P, S, T and Y were analysed with the Kepler image analysis system. The spot volume data of the 12 analysed patterns were corrected for the unequal labeling efficiencies of the ³H amino acids and for the various exposure times. This correction is performed by applying calibration factors based on the amino acid determination of a hydrolysate of the analysed cells. After the calibration step was applied to the data files we used the amino acid compositions of nine proteins taken from a database to establish for each of these proteins the correlation coefficients with the image analysis derived amino acid compositions of all spots. The correlation coefficients allow us to tentatively identify polypeptide spots on two-dimensional gels, while the amino acid composition of 350 investigated two-dimensional gel spots is usable as an identification tag in the gene retrieval from our cDNA libraries.