No abstract

The properties of native streptokinase and streptokinase purified from the human plasminogen activator complex (altered streptokinase) have been compared. Native streptokinase possesses a molecular weight of 44,000 and a s°o,w value of 3.03 S whereas the values for altered streptokinase are 36,000 and 2.82 S, respectively. Native streptokinase possesses an amino-terminal isoleucine and a carboxylterminal lysine residue whereas altered streptokinase possesses an amino-terminal serine and a carboxyl-terminal lysine residue. The amino-terminal amino acid sequence of native streptokinase is NH2-Ile-Ala-Gly-Pro-Glu-Trp-Leu-Leu-Asp-Arg-Pro-Ser-and the amino-terminal amino acid sequence for altered streptokinase is NH2-Ser-Lys-Pro-Phe-Ala-X-Asp-T A he mechanism of the activation of the single-chain proenzyme, plasminogen to the two-chain enzyme, plasmin by streptokinase has been a widely studied subject. Any study of this mechanism must include the fact that at least one bond in the plasminogen molecule must be cleaved in the activation process (Robbins et al., 1967;Summaria et al., 1967). Although synthetic ester substrates have been found for all other plasminogen activators, none has been found to be a substrate for streptokinase (De Renzo et al., 1967a). This finding appears to rule out direct activation of plasminogen by streptokinase; however, such a mechanism has been nonetheless proposed (Summaria et al., 1969). On the other hand, most investigators have suggested an indirect activation mechanism via an activator complex. It was found that streptokinase could form a 1:1 complex with human plasmin and this complex could in fact directly activate bovine plasminogen (Zybler et al., 1969;Blatt et al., 1964;Ling et al., 1965Ling et al., , 1967). This same activator complex was formed whether streptokinase and human plasmin or streptokinase and human plasminogen were used as the starting materials (Ling et al., 1967). More recently, these considerations have been incorporated into a unified mechanism for the streptokinase induced activation of human plasminogen (Reddy and Markus, 1972) and for the streptokinase-induced activation of rabbit plasminogen (Schick and Castellino, 1973). These studies demonstrate that the principal activator of human plasminogen is a complex of streptokinase and human plasminogen, containing an active site.

No abstract

Normal subjects, patients with various bleeding disorders, and patients with von Willebrand's disease were studied. All patients with von Willebrand's disease had decreased levels of ristocetin-Willebrand factor (range, 0 to 41%) as compared with all other subjects (range, 79 to 202%). Ristocetin-induced platelet aggregation of platelet-rich plasma was abnormal in all patients with von Willebrand's disease tested, and it was possible to correct this abnormal response by addition of normal platelet-poor plasma. Abnormal ristocetin-induced platelet aggregation was seen in patients with intrinsic platelet disorders or, on some occasions, in normal patients who had ingested aspirin. Ristocetin-induced platelet aggregation is not diagnostic, but it may be useful as a simple screening test for patients with possible von Willebrand's disease. In conjunction with other tests, the assay for ristocetin-Willebrand factor will be useful in diagnosis and evaluation of these patients.

Two fractions of rabbit plasminogen have been 86,000 f 3000. These results demonstrate that rabbit plasisolated by specific affinity chromatography on Sepharose minogen consists of a single polypeptide chain. The amino 4B-~-lysine solid supports. Each fraction migrated as a single acid compositions and number of amides in each original but distinct component on polyacrylamide gel electrophoresis fraction were also indistinguishable. Further, on activation at pH 4.3 and each was resolved into five activatable com-to plasmin by urokinase each plasminogen fraction was ponents by polyacrylamide gel electrophoresis at pH 9.5.converted to a two-chain plasmin structure. The molecular Examination of the isozyme pattern in the original fractions weights of the component chains were 62,000 3000 and by isoelectric focusing demonstrated that the first fraction 24,000 f 1800 and were cross-linked in plasmin by disulfide eluted from the affinity columns consisted of five isozymes bond(s). Studies on streptokinase activation demonstrated with an isoelectric pH range of 6.20-7.78. The second frac-that each fraction of rabbit plasminogen is streptokinase tion eluted from the affinity columns also consisted of five sensitive with the component plasmin polypeptide chains isozymes but possessed an isoelectric pH range of 6.95-8.74.indistinguishable in molecular weight to those produced The native molecular weight of each plasminogen fraction by urokinase activation. was 88,000 f 3000 and the subunit molecular weight was