Partial Purification and Characterization of Proteases in Tobacco Leaf and Callus

Ammonium sulfate fra.ctionation, gel permeation and cation-exchange column chromatography were employed for panial purification of proteases from leaf laminae and callus tissues of Samsun NN tobacco (Nicotiana tabacum L). The predominant proteases in the leaf and callus are acidic sulfhydryl proteases which are activated by 2-mercaptoethanol and ethylenediamine tetraacetic acid, completely inhibited- by iodoacetic acid, and partially inhibited by phenylmethane sulfonyl fluoride and pepstatin A. With hemoglobin and tobaccl:l Fraction I protein as substrates, leaf and callus proteases showed a pH optimum of 5. However, specific activity was significandy higher in the callus than in the leaf. Tobacco proteases digested hemoglobin more effectively than Fraction I protein and showed the least activity with casein. Gel permeation resolved three -protease variants in leaf extracts but only two in callus samples. Rechromatography of the large molecular weight fraction in a cation-exchange column produced three and two variants for leaf and callus, respectively. The present results suggest that there are at least five variants of sulfhydryl protease in tobacco leaf and three in callus tissue and that tobacco Fraction I protein can be metabolized by both leaf and callus proteases.