engleski

Binding of Anabolic Steroids to Human Serum Albumin

1. ABSTRACT Binding of testosterone, epitestosterone, and metandienone to human serum albumin (HSA) was studied by the gel filtration method. The experimental results obtained are presented graphically using the method of Scatchard and calculated by linear and non-linear regression: (a) for testosterone and epitestosterone there are two independent and non-equivalent binding sites on the HSA molecule; (b) the binding constants calculated for the higher affinity binding sites were: for epitestosterone K1 /n = 3.7 x 105 L mol-1, and for testosterone = 9.8 x 105 L mol-1 (for the concentration range from 0.64 to 1.12 x 10-5 mol L-1 ); (c) differences estimated between the higher affinity binding site constants were statistically significant (p<0.05); (d) differences between the low affinity binding constants (for concentration range between 1.84 to 7 x 10-5 mol L-1) estimated for testosterone (K2 /n = 0.22 x 105 L mol-1) and for epitestosterone (K2 /n = 0.05 x 105 L mol-1) could not be statistically evaluated because of the high SD values obtained for the low affinity binding of epitestosterone; (e) for metandienone data for Scatchard plot could be best approximated by a single straight line in the whole range of concentration tested (K1 /n = 0.18 x 105 L mol-1) indicating only one set of low affinity binding sites; (f) testosterone, epitestosterone), and metandienone are bound into a low extent to the HSA molecule (i.e. at a ligand concentration of 1.04 x 10-5 mol L-1 the percent of binding ranged from about 23% to 40% for the compounds tested): the higher extent of binding was obtained for testosterone when compared to its isomer epitestosterone (40% and 24%, respectively). Displacement experiments performed using stanozolol revealed that in the presence of the displacement agent, the percent of binding decreased, however, the differences between estimated binding constants were not statistically significant. When binding of metandienone was tested in the presence of stanozolol the results obtained did not allow calculation of the binding parameters by the Scatchard method.

steroids; human serum albumin; binding; binding constants

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