Acetylcholinesterase from the Skeletal Muscle of the Lamprey Petromyzon marinus Exists in Globular and Asymmetric Forms

To obtain information about the evolution of acetylcholinesterase (AChE), we undertook a study of the enzyme from the skeletal muscle of the lamprey Petromyzon marinus , a primitive vertebrate. We found that the cholines‐terase activity of lamprey muscle is due to AChE, not pseudocholinesterase; the enzyme was inhibited by 1,5‐bis(4‐allyldimethylammonium phenyl) pentane‐3‐one (BW284C51), but not by tetramonoisopropyl pyrophos‐phortetramide (iso‐OMPA) or ethopropazine. Also, the enzyme had a high affinity for acetylthiocholine and was inhibited by high concentrations of substrate. A large fraction of the AChE was found to be glycoprotein, since it was precipitated by concanavalin A‐agarose. Optimal extraction of AChE was obtained in a high‐salt detergent‐containing buffer; fractional amounts of enzyme were extracted in buffers lacking salt and/or detergent. These data suggest that globular and asymmetric forms of AChE are present. On sucrose gradients, enzyme that was extracted in high‐salt detergent‐containing buffer sedimented as a broad peak of activity corresponding to G 4 ; additionally, there was usually a peak corresponding to A 12 . Sequential extraction of AChE in conjunction with velocity sedimentation resolved minor forms of AChE and revealed that the G 1, G 2 , G 4 , A 4 , A 8 , and A 12 forms of AChE cpuld be obtained from the muscle. The identity of the forms was confirmed through high‐salt precipitation and collagenase digestion. The asymmetric forms of AChE were precipitated in low ionic strength buffer, and their sedimentation coefficients were shifted to higher values by collagenase digestion. We discuss these results in terms of the evolution of AChE in deuterostome vertebrates and invertebrates and in terms of the physiological significance of asymmetric forms of AChE for muscle function.