Intrinsic forms of acetylcholinesterase in skeletal muscle

In~~d~~tionAcetylcholinesterase (AChE; EC 3.1.1.7)occurs in mammalian and avian skeletal muscle in a number of molecular forms as characterised by their sedimentation coefficients on sucrose gradients.In rat diaphragm, three principal forms were observed by Hall ]I] , who showed that the heaviest (H) form, 16 S AChE, was specifically associated with the endplate regions of the muscle and was greatly reduced in amount upon denervation.Vigny et al. [2,3] provided additional evidence suggesting that the H form was endplatespecific in various muscles of the rat and the chicken.In all 3 studies, however, the H form accounted for only a minor part of the total AChE activity, the greater part of the enzyme occurring in peaks of medium ($4) or low (L) sedimentation coefficient.Treatment with collagenase or proteases can modify the molecular forms of AChE in skeletal muscle [4][5][6] , and it has been suggested that endogenous proteases may affect the distribution of AChE species observed in skeletal muscle extracts [ 5,7] .In the present study, therefore, we have examined the effect of certain protease inhibitors on the sedimentation profile of AChE activity in extracts of various chicken muscles and of rat diaphragm.We will demonstrate that use of protease inhibitors in the extraction medium prevents degradation of the intrinsic molecular forms of AChE and.greatly simplifies the sedimentation profiles obtained, Using an appropriate mature of ~hibitors, it is shown that AChE in normal pectoral muscle is predominantly of the H (19.5 S) type.In the pectoral