[A study of native streptokinase and its polymeric derivative by means of small angle x-ray scattering]

The gyration radius (R0) of native streptokinase (SK) was found to be R0 = (40 +/- ) A by small-angle X-ray scattering. Experimental hydrodynamic characteristics of SK were S0(20),W = (2.8 +/- 0.1)S; D0(20),W = (6.0 +/- 0.5) x 10(-7) cm2/s; [n] = 0.12 dl/g. The molecular weight of the enzyme was found to be 44,000. The values of the form factor R0/Rsphere = 2.1 and the frictional ratio f/f0 = 1.5 indicate considerable anisometry of the SK molecule. Basing on the curves of small-angle X-ray scattering of SK modified with a synthetic linear copolymer of N-vinylpyrrolidone (P) at a molar ratio SK less than P, a structural model of the conjugate was proposed. The modified form consisted of a dense nucleus covered with a diffuse polymeric membrane. In accordance with the model, R0 of modified SK and of the whole conjugate were found to be R0nucleus = (34 +/- 2) A and R0conjugate = (114 +/- 5)A.