Biochemistry. 1976 Apr 6;15(7):1425-34. |
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Molecular forms of acetylcholinesterase
from Torpedo californica: their relationship to synaptic membranes.
Lwebuga-Mukasa JS, Lappi S, Taylor P.
The 16S and 8S forms of acetylcholinesterase (AchE), which are composed of
an elongated tail structure in addition to the more globular catalytic subunits,
were extracted and purified from membranes from Torpedo californica electric
organs. Their subunit compositions and quaternary structures were compared
with 11S lytic enzyme which is derived from collagenase or trypsin treatment
of the membranes and devoid of the tail unit. Upon sodium dodecyl sulfate-polyacrylamide
gel electrophoresis in the absence of reducing agent, appreciable populations
of monomeric through tetrameric species are observed for the 11S form. Under
the same conditions, the 16S form yields only monomer and dimer in addition
to a higher molecular weight species. If complete reduction is effected, only
the 80,000 molecular weight monomer is dominant for both the 11S and 16S forms.
Cross-linking of the 11S form by dimethyl suberimidate followed
by reduction yields monomer through tetramer in descending frequency, while
the 16S form again shows a high molecular weight species. A comparison
of the composition of the 11S and 16S forms reveals that the latter has an
increased glycine content, and 1.1 and 0.3 mol % hydroxyproline and
hydroxylysine, respectively. Collagenases that have been purified to homogencity
and are devoid of amidase and caseinolytic activity, but active against native
collagen, will convert 16S acetylcholinesterase to the 11S form. Thus, composition
and substrate behavior of the 16S enzyme are indicative of the tail unit containing
a collagen-like sequence. A membrane fraction enriched in acetylcholinesterase
and components of basement membrane can be separated from the major portion
of the membrane protein. The 16S but not the 11S form reassociates selectively
with this membrane fraction. These findings reveal distinct similarities between
the tail unit of acetylcholinesterase and basement membrane components and
suggest a primary association of AchE with the basement membrane.
PMID: 177042 [PubMed - indexed for MEDLINE]