Clotting of Casein with Pepsin : Amount and Nature of the Soluble Products

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The amounts of soluble products resulting from the action of pepsin on whole casein at pH 6.5 have been determined by precipitating the solutions with CaCl2 (clot formation), and with 12% trichloracetic acid, and by adjusting the pH to 4.7 with HCl. α- and β-Caseins were studied in the same manner; with the latter, however, no clot was obtained. In general, 2 to 5% of the whole casein and α-casein N became soluble by the action of pepsin, with the lower values obtained with trichloracetic acid as the precipitant. Parallel increases in soluble P were obtained. Both paper and column chromatography showed that the soluble fractions contained a number of components, none of which were free amino acids or orthophosphate. Increases in the soluble fraction of β-casein indicated that considerable proteolysis had occurred. Most of the soluble fractions did not pass through a cellophane membrane.

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When tomatoes were planted in steamed soil inoculated with spores of Didymella lycopersici Kleb., a large proportion became infected but very few became infected in unsteamed soil similarly inoculated. In soil treated with formalin and subsequently inoculated the number of diseased plants was about half that in steamed soil. Reinfecting steamed soil with soil micro-organisms before inoculation with D. lycopersici reduced the amount of disease. Covering steamed soil with a layer of maiden loam filtered out a large proportion of D. lycopersici spores applied in water suspension and reduced the amount of disease. Addition of stable manure either before or after steaming did not affect the number of diseased plants Steamed soil remained susceptible to infection by D. lycopersici for 4 months