Acrylamide photopolymerization at 25 degrees C, using as chain transfer agent the single exposed cysteine residue of bovine serum albumin (BSA), resulted in a conjugate where a single poly(acrylamide) chain is bound to the cysteine residue of the protein. Studies of the intrinsic fluorescence of the protein and of the extrinsic probe, 1-anilino-8-naphthalene-sulfonic acid, indicate that the protein mostly maintains its native structure in the conjugate. Kinetic studies showed that the chain transfer efficiency of thiols depends on the microenvironment where the -SH group is located. The single exposed cysteine residue of BSA is a more efficient chain transfer agent of the acrylamide polymerization than the free cysteine or glutathione tripeptide. Other potentially reactive amino acids, such as tryptophan, tyrosine and histidine, are two orders of magnitude less efficient than the protein as chain transfer agents. (C) 2010 Elsevier Ltd. All rights reserved.