The extracellular bacterial protein, streptokinase, is produced by various strains of P-hemolytic streptococci (Streptococcus haemolyticus). Billroth first identified streptokinase-producing streptococci in 1874 in exudates of infected wounds. The thrombolytic effect of streptokinase, which was initially called streptococcal fibrinolysin, was first demonstrated in 1933 . In the same year, serological distinctions allowed further differentiation of the P-hemolytic streptococci into groups A to O . Most of the streptokinases are obtained from P-hemolytic streptococci of the groups A, C, and G. The C group is preferred for producing the protein as it lacks erythrogenic toxins. The group C strain Streptococcus equisimilis H46A (ATCC 12449) isolated from a human source in 1945 has been widely used for producing streptokinase because it synthesized the most thrombolytically active form. The H46A strain is also the main source of the streptokinase gene (skc), which has been studied in detail and expressed in various other microorganisms [35,36].
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