1. By radiolabelling, polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate and fluorography, more than 50 soluble proteins in the molecular-weight range 15000–100000 were shown to continue to be synthesized after cells had been isolated from rat gastric mucosa. 2. Densitometric measurements of stained gels and fluorographic films were processed by computer to resolve individual overlapping Gaussian peaks corresponding to the protein bands. 3. Comparison of resolved peak areas of radioactivity and staining showed certain bands to have characteristically high relative specific radioactivities. 4. The computer programs (in FORTRAN) permit the analysis of a single densitometric trace or the simultaneous comparison of a corresponding pair of densitometric records of stained gels, or of fluorographic films, or a combination. Central processing unit time is used economically. 5. The programs identify the Gaussian components that contribute to the records and estimate their means, standard deviations and enclosed areas. These estimates are improved by a piecewise iterative method that minimizes the errors between the calculated and the experimental data. 6. Relative specific radioactivities are calculated as the normalized ratio of the area of a fluorographic film peak and the area of the corresponding stained gel peak. The computer programs have been deposited as Supplementary Publication SUP 50094 (55 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms given in Biochem. J. (1978) 169, 5.

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