ABSTRACT
11 S acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) from
the electric eel Electrophorus electricus essentially consists of four
catalytic subunits which appear to be identical structurally but to be
assembled with slight asymmetry. During isolation and storage of the enzyme,
proteolysis cleaves a portion of the subunits into major fragments containing
the active site and minor fragments containing no active sites without
change in the enzyme molecular weight. A previous report (Gentinetta, R.
and Brodbeck, U. (1976) Biochim. Biophys. Acta 438 437--448) indicated
that the intact and the fragmented subunits reacted with diisopropylfluorophosphate
at different rates and that the reaction rate in the presence of excess
phosphorylating agent was not strictly first order. Those findings could
not be reproduced in this report. Intact and fragmented subunits were observed
to react at the same rate with diisopropylfluorophosphate. In addition,
the overall reaction kinetics both of 11 S and 18 S plus 14 S acetylcholinesterase
were found to be strictly first order in the presence of an excess of diisopropylfluorophosphate
throughout the course of reaction. These results are consistent with several
previous reports that only one type of active site can be detected in acetylcholinesterase.
The proteolysis which fragments a portion of the catalytic subunit has
no apparent effect on the catalytic properties of the enzyme.
MEDLINE PMID: 454619
Chemical Abstracts: 90:163995