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Binding of 5 alpha-dihydroprogesterone to proteins in human pregnancy serum
Abstract:
The binding of 5 alpha-dihydroprogesterone (DHP) to proteins in pregnancy serum has been investigated and compared with the binding of progesterone. Characteristic properties of the DHP-serum protein interaction were unsaturability, low affinity and poor complex stability. Fractionation of serum using a variety of protein separation techniques, revealed that DHP interacts with several proteins. At low temperature (0--4 degrees C) albumin appeared to be the principal binding component whereas higher temperatures seemed to favour binding to beta-lipoproteins and alpha 2-macroglobulin. Binding to specific binding proteins such as the corticosteroid binding globulin (CBG) and the sex hormone-binding globulin, (SHBG) were detectable but appeared to be quantitatively unimportant. Progesterone showed a similar multicomponent interaction but differed from DHP in the extent of binding to CBG. Binding of either hormone to the alpha 1-acid-glycoprotein was negligible. The present study shows that the high endogenous DHP levels present in pregnancy sera are caused by factors other than high affinity protein binding.
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