278
R. M. C. DAWSON
brain, heart, spleen, and whole blood as well as sheep liver and thyroid
(2, 64) and pig lung (55). Recent evidence suggests that it may also
be present in human plasma. The mammalian tissue enzyme has a pH
optimum of 6.0-6.5; this is much higher than that of the phospholipase
B of molds.
Phospholipase B has been prepared from fresh extracts of rice bran
or Aspergillus oryzae (65); the mycelium of Penicillium notatum is also
a rich source (66) as well as that of Penicillium chrysogenum
(67).
The enzyme from mold has been partially purified with ammonium
sulfate (64, 68). It has a low pH optimum, which has been found with
various preparations to vary between 3.3 and 4 (59, 65, 66).
In bacteria, phospholipase B has been characterized in Serratki plymuthica; it has a pH optimum of 6.0 and differs from the enzyme prepared from other sources in having remarkable thermal stability (38).
It has been found also in Mycobacterium avium, the avian tubercule
bacillus (69), and in a preparation of microorganisms from sheep rumen
(70). The partially purified enzyme from the latter source, which could
be derived from either protozoa or bacteria, has a pH optimum of 7.5,
which is higher than the phospholipase B from other sources.
Phospholipase B does not occur in the poison of snakes, but with
the venoms of the bee, hornet (Vespa crabro), and wasp, the lysolecithin formed by the action of phospholipase A is further broken down
to glycerylphosphorylcholine (65, 71, 72).
C. GLYCERYLPHOSPHORYLCHOLINE DIESTERASE
The glycerylphosphorylcholine and glycerylphosphorylethanolamine
formed by the action of phospholipase B can be further metabolized by
the enzyme glycerylphosphorylcholine diesterase, which catalyzes the
hydrolysis of both these phosphodiesters, liberating the free base and
glycerophosphoric acid. The enzyme has been characterized in mammalian tissues [rat liver, kidney, heart, brain, spleen, intestine, skeletal
muscle, and blood cells (73) and in various parts of the nervous system
in the rat, guinea pig, hen, human, rabbit, and dog (74)] and also in
the bacterium Serratia plymuthica (38). The enzyme does not appear
to be present in significant amounts in sheep liver (73) or in pancreas
(63).
Soluble preparations of the liver enzyme require Mg
2+ for full activity,
although high concentrations are inhibitory (73). The bacterial enzyme
is inhibited by Mg
2+ and also by metal chelating agents such as Versene
(38). The pH optimum of the rat liver enzyme is 7.5; of the bacterial
enzyme, 9.0; and of rat brain homogenates, 9.5.
R. M. C. DAWSON
brain, heart, spleen, and whole blood as well as sheep liver and thyroid
(2, 64) and pig lung (55). Recent evidence suggests that it may also
be present in human plasma. The mammalian tissue enzyme has a pH
optimum of 6.0-6.5; this is much higher than that of the phospholipase
B of molds.
Phospholipase B has been prepared from fresh extracts of rice bran
or Aspergillus oryzae (65); the mycelium of Penicillium notatum is also
a rich source (66) as well as that of Penicillium chrysogenum
(67).
The enzyme from mold has been partially purified with ammonium
sulfate (64, 68). It has a low pH optimum, which has been found with
various preparations to vary between 3.3 and 4 (59, 65, 66).
In bacteria, phospholipase B has been characterized in Serratki plymuthica; it has a pH optimum of 6.0 and differs from the enzyme prepared from other sources in having remarkable thermal stability (38).
It has been found also in Mycobacterium avium, the avian tubercule
bacillus (69), and in a preparation of microorganisms from sheep rumen
(70). The partially purified enzyme from the latter source, which could
be derived from either protozoa or bacteria, has a pH optimum of 7.5,
which is higher than the phospholipase B from other sources.
Phospholipase B does not occur in the poison of snakes, but with
the venoms of the bee, hornet (Vespa crabro), and wasp, the lysolecithin formed by the action of phospholipase A is further broken down
to glycerylphosphorylcholine (65, 71, 72).
C. GLYCERYLPHOSPHORYLCHOLINE DIESTERASE
The glycerylphosphorylcholine and glycerylphosphorylethanolamine
formed by the action of phospholipase B can be further metabolized by
the enzyme glycerylphosphorylcholine diesterase, which catalyzes the
hydrolysis of both these phosphodiesters, liberating the free base and
glycerophosphoric acid. The enzyme has been characterized in mammalian tissues [rat liver, kidney, heart, brain, spleen, intestine, skeletal
muscle, and blood cells (73) and in various parts of the nervous system
in the rat, guinea pig, hen, human, rabbit, and dog (74)] and also in
the bacterium Serratia plymuthica (38). The enzyme does not appear
to be present in significant amounts in sheep liver (73) or in pancreas
(63).
Soluble preparations of the liver enzyme require Mg
2+ for full activity,
although high concentrations are inhibitory (73). The bacterial enzyme
is inhibited by Mg
2+ and also by metal chelating agents such as Versene
(38). The pH optimum of the rat liver enzyme is 7.5; of the bacterial
enzyme, 9.0; and of rat brain homogenates, 9.5.