[Studies of the heterogeneity of streptokinases; IV. Evidence for isostreptokinases in Streptococcus pyogenes type 1 (author's transl)].

Two strains of Streptococcus pyogenes, originating from the same Griffith strain SF 130/13 but different in M protein synthesis, produce two isostreptokinases. The molecular weights of both isostreptokinases are the same (about 50 000 daltons) as well as the specific activities (38 000 and 43 000 U/mg, resp.). The activity values are influenced by an incomplete removal of ampholytes. The isoelectric points were determined as pI 6.3, and 6.5, resp. The presence of isostreptokinases was concluded by (1) the absence of proteolytic activities in the culture filtrate, (2) the same molecular weights, (3) the same specific activities, (4) the constant quantitative relation of about 1:2.5 between both isostreptokinases after refocusing, (5) a lack of cystein- or cystin residues in the molecule, (6) the appearance of both isostreptokinases in untreated culture filtrates, (7) the separability by disc electrophoresis, and (8) the lack of such double bands in streptokinases of other streptococci. Isoelectric focusing of streptokinase produced by a type 3 strain of S. pyogenes was followed by the appearance of four bands with streptokinase activity. It is unlikely that these four bands represent isostreptokinases. Both streptokinases (type 1 and type 3 streptococci) differ from streptokinases of other types by their relatively high content of tryptophane (table 1) and the high isoelectric points (6.5 to 6.0; streptokinases of other types and groups show pI's between 5.05 to 5.65 (6).