The objective of the present study was to analyze serum protein complexes and detect serum esterase activities using nongradient blue native polyacrylamide gel electrophoresis (BN-PAGE). For analysis of potential protein complexes, serum from rat was used. Results demonstrate that a total of 8 gel bands could be clearly distinguished after Coomassie blue staining, and serum albumin could be isolated nearly as a pure protein. Moreover, proteins in these bands were identified by electrospray mass spectrometry and low-energy collision induced dissociation (CID)-MS/MS peptide sequencing and the existence of serum dihydrolipoamide dehydrogenase (DLDH) was confirmed. For studies of in-gel detection of esterase activities, serum from rat, mouse, and human was used. In-gel staining of esterase activity was achieved by the use of either α-naphthylacetate or β-naphthylacetate in the presence of Fast blue BB salt. There were three bands exhibiting esterase activities in the serum of both rat and mouse. In contrast, there was only one band showing esterase activity staining in the human serum. When serum samples were treated with varying concentrations of urea, esterase activity staining was abolished for all the bands except the one containing esterase 1 (Es1) protein that is known to be a single polypeptide enzyme, indicating that majority of these esterases were protein complexes or multimeric proteins. We also identified the human serum esterase as butyrylcholinesterase following isolation and partial purification using ammonium sulfate fractioning and ion exchange column chromatographies. Where applicable, demonstrations of the gel-based method for measuring serum esterase activities under physiological or pathophysiological conditions were illustrated. Results of the present study demonstrate that nongradient BN-PAGE can serve as a feasible analytical tool for proteomic and enzymatic analysis of serum proteins.
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