Approximately 150/o of the total acetylcholinesterase (AChE)
activity of pig brain cortex can be extracted in dilute buffer solution
and the properties of this »soluble« form of the enzyme have been
compared with the membrane bound enzyme which was brought
into solution by extraction with 1-0/o Triton X-100 or 1 mM EDTA.
The activity of the »soluble« enzyme against a range of ·substrates is
identical to the membrane enzyme. The variation of activity with
pH and substrate concentration are similar for the two phyisical
forms of the AChE. Gradient polyacrylamide gel electrophoresis
demonstrated the similarities of the »soluble« and detergent solubilized
enzyme preparations. Three molecular weight species were
common to both preparations: 353 000, 262 000, and 68 000 and in
addition the »soluble« enzyme had a band of mol. wt. 135 000 while
the Triton X - 100 extract contained species of mol. wt. 181 000
and 83 000. The membrane AChE showed a break in the Arrhenius plot
with a transition temperature of 27 °c and this was abolished with
detergent. In contrast the »soluble« enzyime showed no break in
the Arrhenius plot suggesting the absence of associated membrane
material. There are however more similarities than differences
between the two physical forms of the enzyme which appear to be
closely related
