Interaction of AChE with Lens culinaris agglutinin reveals differences in glycosylation of molecular forms in sarcoplasmic reticulum membrane subfractions.

Fractionation of muscle microsomes rich in sarcoplasmic reticulum (SR) by isopicnic centrifugation yielded three types of membranes. Heavy (HM), intermediate (IM), and light membranes (LM), with isopicnic points of 38, 33, and 25% w/w sucrose, were rich in terminal cisternae/triads, longitudinal SR, and T-tubules, respectively. All membrane subfractions displayed acetylcholinesterase (AChE) activity. About 60, 80, and 50% of total AChE in HM, IM, and LM was extracted with a Tris-saline-Triton buffer. AChE molecular forms of 4.5 S (G1), 10.5 S (G4), and 16 S (A12) were found in all membranes but their relative proportion varied among the several membranes. Asymmetric and tetrameric forms were partly sedimented with Lens culinaris agglutinin (LCA), but most of the monomeric AChE failed to interact with the lectin. However, some of the monomers, exclusively found in LM, reacted with LCA. The data suggest that monomeric AChE is classified in rough endoplasmic reticulum. A subset is destined to SR, a second one converted into oligomeric forms, and a third one is associated to external membrane after passing through the Golgi system.