Developmental changes in the molecular forms of acetylcholinesterase during the life cycle of the lamprey Petromyzon marinus.

1. We have determined the molecular forms of acetylcholinesterase (AChE) present in the skeletal muscle of the lamprey during the adult parasitic stage of its life cycle. AChE was found primarily in the globular G4 form, as well as in the asymmetric forms A4, A8 and A12. 2. We compare the complement of molecular forms present in skeletal muscle during the larval, parasitic, and spawning stages of the lamprey life cycle. The larval form, the ammocoete, contains elevated amounts of G1 and G2. However, the most striking change that we observed was in the proportion of asymmetric forms of AChE present: 5% in the ammocoete, 28% in the parasite and 9% in the spawner. 3. We speculate that these differences may be related to the physiological states of the lamprey during the various stages of its life cycle.