A Study of the Molecular Sizes and Stability of Choline Acety Ltransfer Ase

Aggregation of the enzyme acetyl‐CoA: choline‐O‐acetyltransferase (ChAc, EC 2.3.1.6) which appears to be homogeneous has been observed. The molecular weight of the most abundant form of ChAc was estimated by gel filtration and sucrose gradient centrifugation to be in the range 58,000‐62,000. The most frequently encountered aggregates were much larger and eluted in the void volume from Sephadcx® G‐100 and G‐150 indicating molecular weights in excess of 400,000. In fact, they were subsequently found to be 1.2 × 106 and 1.9 × 106 by sucrose gradient centrifugation. The percentage of activity associated with high molecular weight ChAc increased with purification, but these aggregates disappeared after storage for 2‐3 weeks at −20°C. The loss occurred independently of any fall in enzymic activity in the preparations examined.