6. METABOLISM OF PHOSPHOLIPIDS
279
D. PHOSPHOLIPASE C
1. Properties
This phospholipase catalyzes the hydrolysis of lecithin, liberating a
1,2-diglyceride and phosphorylcholine. Both fully saturated and unsaturated lecithins are attacked (75), and also choline plasmalogen.
Sphingomyelin is hydrolyzed with the formation of phosphorylcholine
and a ceramide, but phosphatidylserine, phosphatidylethanolamine, and
lysolecithin are not usually attacked (75, 75a) although there is some
evidence that they can be hydrolyzed when they are presented to the
enzyme in a mixed phospholipid substrate (75b).
The activity of the enzyme under normal conditions of assay requires the presence of calcium as an activator (76). To a lesser extent
magnesium, maganese, cobalt, and zinc can activate the system, but
cuprous, strontium, cadmium, aluminum, ferrous, ferric, and barium
ions are inhibitory (77). Phospholipase C is similar to the A and D
enzymes in showing considerable resistance to heat and also by its
ability to act catalytically in wet ether solution of its substrate (75).
The enzyme has been partially purified by ammonium sulfate and
nucleic acid precipitation (78) and by methanol solvent fractionation
(79).
2. Distribution
Phospholipase C appears to be largely confined to the plant kingdom
although reports, as yet unconfirmed, have appeared of its presence
in fetal pig cartilage (80) dog brain, rabbit pancreas, ox kidneys (81),
human semen (82), and the venom of the snake Bothrops alternatus
(47).
In bacteria, phospholipase C is identical with the α-toxin of Clostridium perfringens (welchii) and also that of C. bifermentans
(83).
It is also found in C. hemolyticum (84) and C. oedematiens
(novyi)
(85). Although the enzymes from these species all catalyze the identical
chemical reaction, they are not by any means identical proteins. For
example, in C. oedematiens filtrates two immunologically distinct lecithinases are present; these probably represent the γ- and ß-toxins. The
phospholipase in C. hemolyticum is apparently identical antigenically
with C. oedematiens ß-toxin, but not with the γ-toxin or the α-toxin of
C. perfringens. The C. bifermentans lecithinase is inhibited by C. perfringins antitoxin; this suggests similarity of structure, but nevertheless,
the two lecithinases show appreciable differences in their biochemical
279
D. PHOSPHOLIPASE C
1. Properties
This phospholipase catalyzes the hydrolysis of lecithin, liberating a
1,2-diglyceride and phosphorylcholine. Both fully saturated and unsaturated lecithins are attacked (75), and also choline plasmalogen.
Sphingomyelin is hydrolyzed with the formation of phosphorylcholine
and a ceramide, but phosphatidylserine, phosphatidylethanolamine, and
lysolecithin are not usually attacked (75, 75a) although there is some
evidence that they can be hydrolyzed when they are presented to the
enzyme in a mixed phospholipid substrate (75b).
The activity of the enzyme under normal conditions of assay requires the presence of calcium as an activator (76). To a lesser extent
magnesium, maganese, cobalt, and zinc can activate the system, but
cuprous, strontium, cadmium, aluminum, ferrous, ferric, and barium
ions are inhibitory (77). Phospholipase C is similar to the A and D
enzymes in showing considerable resistance to heat and also by its
ability to act catalytically in wet ether solution of its substrate (75).
The enzyme has been partially purified by ammonium sulfate and
nucleic acid precipitation (78) and by methanol solvent fractionation
(79).
2. Distribution
Phospholipase C appears to be largely confined to the plant kingdom
although reports, as yet unconfirmed, have appeared of its presence
in fetal pig cartilage (80) dog brain, rabbit pancreas, ox kidneys (81),
human semen (82), and the venom of the snake Bothrops alternatus
(47).
In bacteria, phospholipase C is identical with the α-toxin of Clostridium perfringens (welchii) and also that of C. bifermentans
(83).
It is also found in C. hemolyticum (84) and C. oedematiens
(novyi)
(85). Although the enzymes from these species all catalyze the identical
chemical reaction, they are not by any means identical proteins. For
example, in C. oedematiens filtrates two immunologically distinct lecithinases are present; these probably represent the γ- and ß-toxins. The
phospholipase in C. hemolyticum is apparently identical antigenically
with C. oedematiens ß-toxin, but not with the γ-toxin or the α-toxin of
C. perfringens. The C. bifermentans lecithinase is inhibited by C. perfringins antitoxin; this suggests similarity of structure, but nevertheless,
the two lecithinases show appreciable differences in their biochemical