FINE STRUCTURAL LOCALIZATION OF ACETYLCHOLINESTERASE USING ACETYL-β-METHYLTHIOCHOLINE AND ACETYLSELENOCHOLINE AS SUBSTRATES

Acetyl-β-methylthiocho1ine and acetylselenocholine were used as substrates for fine structural demonstration of acetylcholinesterase activity and were compared with acetylthiocholine. Essentially, the same localization of the enzyme activity was found with all of these substrates in the rat spinal cord. Acetyl-β-methylthiocoline proved to be the most specific for acetylcholinesterase in the cytochemical system used and the final product was deposited most rapidly with acetylselenocholine. When the method of Karnovsky and Roots was modified by substituting tartrate for citrate as a chelating agent, a fine crystalline end product was produced and a sharp localization with little evidence of diffusion was obtained. A fixative containing a mixture of formaldehyde and glutaraldehyde proved to be the best in preserving both enzyme activity and ultrastructure. The substrates were tested biochemically and the results substantiate the cytochemical data.