Antistreptokinase IgG (antiSK
IgG) from blood of 8 patients with acute
myocardial infarction that were treated by
streptokinase (SK) has been investigated. AntiSK
IgG contained 1.8% of total serum
IgG. They had high affinity to SK (K50% approximately 10 nM) and inhibited activation of
plasminogen (Pg) by SK with K50% approximately 6 nM. AntiSK
IgG were bound with chymothriptic fragments of SK with affinity decreased in the set of fragments: 47 > 36 > 30 > 17 > or = 11 > 7 kDa. 11 linear
epitopes of antiSK
IgG were localized in I1-S12, T43-M70, G139-Q152, T163-I190, T193-S222, F241-Y252, Y275-P286, T315-L336, I365-E376, S379-T390 and Y397-N410 sites of SK primary structure using SK decapeptides. 70% of
antibodies were bound with T43-M70 (38.3%), T315-L336 (13.2%) and Y397-N410 (17.7%) SK sequences located in alpha and gamma SK domains. By depletion of antiSK
IgG on Pg-SK complex it was shown that 80-85% of antiSK
IgG bound to Pg-SK complex, 47.9% of that contained
antibodies with
epitopes located in I1-S12, T43-M70, T193-S222 and S379-T390 SK sequences, and rest of
IgG had probably spatial
epitopes. Unbound with Pg-SK complex
antibodies inhibited activation of Pg by SK with higher affinity (Ki approximately 1.2 nM) in comparison with total antiSK
IgG fraction. The role of different sites in antigenity of SK and in Pg-SK complex formation is discussed.