Comparison of the subunits of Torpedo californica acetylcholine receptor by peptide mapping

Abstract

The acetylcholine receptor from T. californica electroplax was purified approximately 100-fold by affinity chromatography on .alpha.-neurotoxin-Sepharose 6B. Four putative subunits (.alpha., .beta., .gamma., .delta.) of apparent MW of 43,000, 52,000, 58,000 and 63,000 were found when the purified material was analyzed by sodium dodecyl sulfate (NaDodSO4) gel electrophoresis. In some preparations the amount of the .gamma. polypeptide was small. The presence of N-ethylmaleimide throughout the purification procedure greatly enhanced the amount of the .gamma. chain. To investigate the possibility that the putative subunits may be structurally related, they were isolated by preparative NaDodSO4 gel electrophoresis and subjected to peptide mapping analyses. The patterns of fragments generated by Staphylococcus aureus V8 protease, papain, or chymotrypsin were different for each of the polypeptides. Thus, it is unlikely that they are derivatives of each other.