Recent Progress in the Biochemistry of Choline Acetyltransferase

Abstract

This chapter discusses recent progress in the biochemistry of choline acetyltransferase (ACh). Ach, which is generally accepted as a neurotransmitter both at the peripheral and central cholinergic synapses is synthesized by the reversible transfer of acetyl groups from acetyl-CoA to choline catalyzed by the enzyme choline acetyltransferase (ChAT). In the recent years, great progress has been achieved in the purification of the ChAT. The progress is mainly due to improved techniques in column chromatography, fractionation techniques, affinity chromatography and in stabilizing the purified enzyme. Several laboratories have prepared enzyme preparations with specific activity higher than 20 pmollmin mg protein. Different molecular forms of ChAT exist both as charge isoenzymes and as aggregates. However, the presence of aggregates seems to be dependent upon experimental conditions. Various reaction mechanisms have been proposed for ChAT. Strong evidence has been presented that a histidine residue in the active site participates in the acetyl transfer reaction. Antibodies raised against bovine brain ChAT inactivate ChAT almost completely in immunoprecipitation experiments. The antibodies crossreact with several species those are important in terms of immunohistochemical localization of ChAT. However, the specificity of several of the antibody preparations is still questioned, although encouraging results have recently been obtained in preparing monospecific antibodies against bovine brain ChAT of high specific activity.