Membrane affinities and subcellular distribution of the different molecular forms of choline acetyltransferase from rat.

Abstract

AbstractCholine acetyltransferase from rat brain is present in three different molecular forms with isoelectric points at pH 7·4‐7.6, 7·7‐7·9 and 8·3. The three forms were identified in a highly purified enzyme preparation, in a preparation of synaptosomes and in a cyto‐plasmic preparation from disrupted axons and perikarya (fraction S3). The three molecular forms differed in their affinities for synaptosome membranes and for a cation exchange resin (CM‐Sephadex C‐50). The positive surface charges of the different molecular forms and their affinities for membranes correlated well with their isoelectric points. The molecular form with jsoelectric point 8·3 had the largest positive surface charge and the highest membrane affinity. On isoelectric focusing of an extract from rat brain synaptosomes, the molecular form with isoelectric point 8·3 formed a complex with a negatively charged compound, presumably a protein. A method was developed to remove this compound by treatment with DEAE‐Sephadex or by precipitation with vinblastine. These procedures are similar to methods known to remove the neurotubular protein. The complex formation did not occur in fraction S3.