Federation Proceedings 37:1527, (1978).
A RESIDUAL SUBUNIT FRAGMENT IN THE CONVERSION OF 18S TO 11S ACETYLCHOLINESTERASE. Philip Barnett* and Terrone L. Rosenberry. Depts. of Biochemistry and Neurology, Columbia Univ., New York, N.Y. 10032.
11 S Acetylcholinesterase (AChE) purified by affinity chromatography from toluene-stored eel electric organ is a tetramer of catalytic subunits. Prior to disulfide reduction , the predominant species in denaturing solvents is a 150,000 MW disulfide linked dimer of catalytic subunits. If the enzyme is first reduced with dithiothreitol under non-denaturing conditions and the resulting structure alkylated with [14C]N-ethylmaleimide (NEM), the predominant species is a 75,000 MW catalytic monomer containing one alkylated sulfhydryl per monomer. A small peptide of 8,000 apparent molecular weight, originally linked by disulfide bonds to catalytic subunits, is also present and alkylated with NEM. Based on incorporation on NEM, there is one small peptide for each tetramer. 11S AChE is derived from a native 18S species by proteolytic degradation of a collagen-like tail subunit. This small peptide appears to be a residual fragment of the collagen-like subunit that remains after degradation. However, this peptide is not collagen-like; it contains fairly high contents of glutamic acid and proline but no hydroxyproline or hydroxylysine. The collagen-like region of the tail subunit thus appears somewhat removed from the catalytic subunits. (supported by NIH Grants NS-03304-15 and NS-11766-03, NSF Grant PCM73-00744 and a N.Y. Heart Assn. Postdoctoral Fellowship.)