Molecular forms of acetylcholinesterase in chick embryonic fast muscle: developmental changes and effects of DFP treatment.

Multiple molecular forms of acetylcholinesterase (AChE) from embryonic chick pectoral muscle were examined by sucrose density sedimentation. Embryonic muscle in ovo possessed three molecular forms with apparent sedimentation coefficient of 7S, 11S, and 20S. The proportion of the 20S form increased 4-fold between days 11 and 18 in ovo and there was a decrease in the proportion of the 7S and 11S forms. Cultured embryonic muscle contained only 7S and 11S AChE despite the presence of the 20S form in the tissue from which the cultures were derived. Brief treatment with diisopropylphosphorofluoridate (DFP) completely inhibited the enzyme activity; the newly synthesized AChE first appeared as a 7S form. Polyacrylamide gel electrophoresis of the peak fractions from the sucrose gradients revealed that the 7S AChE was composed of two electrophoretic forms and gave evidence that the 20S AChE was too large to enter the running gel. The results are consistent with the ideas that the distribution of AChE molecular forms is regulated during embryonic development and that AChE is first synthesized as a low molecular weight form following inhibition with organophosphate compounds.