Reagent steroid-binding sites

Representative Examples of Affinity Reagents Directed Towards Steroid-Binding Sites... 

Other groups independently have used polyunsaturated ketosteroids as photoaffinity reagents directed towards mammalian steroid-binding proteins. Katzenellenbogen attempted to obtain site-specific photoinactivation and photoattachment of 6-oxoestradiol, Compound XII, to uterine estrogen receptor... 

Based on the foregoing reactions, some useful observations pertaining to the use of A -3-ketosteroids as affinity reagents can be made. First, the chemical specificity of the photoexcited keto group is very broad since both nucleophiles and C—H groups are potential reactants. This would suggest that an enzyme s binding site need not contain reactive nucleophiles in order to be labeled. Second, reactions of the photoexcited steroid with a protein may or may not result in covalent attachment of the steroid to the protein. Third, the possibility of occurrence of nonspecific side reactions is a very real one, particularly in the case of a species that is as reactive as a ketone excited state. 

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