1) Both citrate and acetate can act as acetyl
donors for choline acetylation by crude brain
2) In order to demonstrate the action of acetate
three conditions have to be observed: a) that
acetate is not added as a contaminant of the ATP:
b) that the enzymes bringing acetate into reaction
are protected during extraction from the acetone - dried powder by cysteine: c) that a ten times
higher level of coenzyme than for the citrate
system is used.
á) Citrate acts as an acetyl donor by breaking
down to acetate and oxaloacetate. Mg, ATP and
the coenzyme are essential for this reaction.
The coenzyme requirement is low.
4) Citrate can act in a similar manner in the
acetylation of sulphanilamide. Probably acetate
and oxaloacetate are not the only products of
5 The citrate and acetate "priming reactions"
carried out by the brain enzymes (in the absence
of choline) can be coupled with a liver fraction
(sulphanilamide condensing enzyme) to acetylate
6) At least two steps are involved in enzymic
acetylation. Activation of acetate (probably a coenzyme acetate complex) and condensation with
the acetyl acceptor are the main enzymic steps.
7) "Choline acetylase" includes more than one
enzyme; it should only refer to the enzyme catalysing the condensation of active acetate with
8) The validity of studies on the distribution of
"choline acetylase" in the nervous system is discussed. No change in the ability of various
parts of the system to synthesise acetylcholine is
expected since the "citrate enzyme" probably has a universal distribution.
The Purification and Structure of Coenzyme A.
1) Evidence is presented to prove the identity of th
activator with the coenzyme of acetylation.
2) The coenzyme is not responsible for the blue
fluorescence described by Comline (1948).
3) A method of purification, based on the acidic
and reducing properties of the coenzyme is described.
4) Acid hydrolysatevof the coenzyme contain a sulphur fragment which is probably identical with
the Lactobacillus bulgaricus factor.
5) Digestion of the coenzyme with an enzyme derived from rabbit spleen releases two phosphoruscontaining fragments which can be resynthesised to
the coenzyme by a liver enzyme.
6) Digestion of the coenzyme with a crude intestinal phosphatase releases three phosphorus-containing fragments which cannot be resynthesised
to the coenzyme under the conditions described.