The acetylcholinesterases and non-specific esterases of embryo and chick muscle, brain, heart and other tissues were investigated using acrylamide disc gel electrophoresis and spectrophotometric enzyme assays. Migration of the proteins as a function of acrylamide gel concentration was used to determine their molecular weights and relative charges. Acetylcholinesterase isozymes in embryonic skeletal muscle and brain differed in size but not appreciably in charge. Their molecular weights were approximately 420,000, 300,000 and 220,000. The non-specific esterases of all the tissues studied differed only by charge from each other; their molecular weight averaged 160,000.
Previous experiments indicated that white-fibered muscles from birds selected for muscular dystrophy exhibited acetylcholinesterase isozymes similar to those in embryonic muscle while normal muscles did not. The studies reported here show that the acetylcholinesterases of normal embryo muscle and dystrophic chick muscle migrated similarly on acrylamide gels and responded similarly to anticholinesterase agents. The acetylcholinesterase activity of muscles from chicks of normal females X dystrophic males resembled that of normal chicks. The results are consistent with the hypothesis that white-fibered muscles of birds inbred for muscular dystrophy are unable to repress the synthesis of isozymes of acetylcholinesterase characteristic of normal embryo skeletal muscle.