294
MAURICE WELSCH
explodes unless it is stabilized in a medium of high enough osmotic
pressure (102, 103a).
The degree of bacterial sensitivity to lysozyme is widely different for
different species. It is related to the chemical composition and anatomical
(216) structure of their cell wall (217). In species where the specific
substrate of the enzyme is not readily accessible, normally lysozymeresistant cells can be made sensitive either by suitable pretreatments,
such as lipid extraction or freeze drying followed by rehydration (218),
or by the choice of particular experimental conditions, such as a high
alkalinity, the presence of Versene (219), of glycine (220), etc. (221).
Lysozyme-resistant mutants of the very sensitive species Micrococcus
lysodeikticus appear to owe their peculiar properties to an increase of
the O-acetyl content of their cell wall (222).
Several other bacteriolytic enzymes acting upon different sites of the
basal structure of the bacterial cell wall have been described. They are
found, notably, in cultures of streptomycetes (223, 224), where they
constitute the actinomycetin complex (9, 225, 226), of bacilli (227), and
of other microorganisms as well (228, 229). Some are associated with
bacteriophages, either as an integral part of the virus (230) or as a free
entity produced by the host cell alongside with, but independently of,
the virus
(231-233).
The mode of action of all these enzymes superficially recalls that of
several antibiotics already reviewed: novobiocin, D-cycloserine, the penicillins, bacitracin, and vancomycin (126, 234a). However, although the
final result is the same in all cases, the mechanisms involved are greatly
different: the antibiotics in some way prevent the biosynthesis of the
wall, whereas the enzymes destroy, or impair the mechanical resistance
of, an already existing wall. As a consequence, the latter are able to
dissolve resting, or even killed, bacteria, whereas the former act only
upon metabolically active organisms, their effect resulting precisely from
the unbalanced growth for which they are responsible.
Another enzyme which can exert antibiotic effects is notatin, a flavoprotein with glucose oxidase activity, produced by Penicillium notatum,
P. vitale (234b), and other species. It is indirectly bactericidal through
its ability to produce the toxic hydrogen peroxide. The same kind of
antibiotic effect was reported for xanthine oxidase in the presence of
xanthine.
Antagonistic relations observed between mouth microorganisms and
the antibiotic activity of pneumococci have been explained by a similar
mechanism.
In closing this section, it should be recalled that several proteins from
MAURICE WELSCH
explodes unless it is stabilized in a medium of high enough osmotic
pressure (102, 103a).
The degree of bacterial sensitivity to lysozyme is widely different for
different species. It is related to the chemical composition and anatomical
(216) structure of their cell wall (217). In species where the specific
substrate of the enzyme is not readily accessible, normally lysozymeresistant cells can be made sensitive either by suitable pretreatments,
such as lipid extraction or freeze drying followed by rehydration (218),
or by the choice of particular experimental conditions, such as a high
alkalinity, the presence of Versene (219), of glycine (220), etc. (221).
Lysozyme-resistant mutants of the very sensitive species Micrococcus
lysodeikticus appear to owe their peculiar properties to an increase of
the O-acetyl content of their cell wall (222).
Several other bacteriolytic enzymes acting upon different sites of the
basal structure of the bacterial cell wall have been described. They are
found, notably, in cultures of streptomycetes (223, 224), where they
constitute the actinomycetin complex (9, 225, 226), of bacilli (227), and
of other microorganisms as well (228, 229). Some are associated with
bacteriophages, either as an integral part of the virus (230) or as a free
entity produced by the host cell alongside with, but independently of,
the virus
(231-233).
The mode of action of all these enzymes superficially recalls that of
several antibiotics already reviewed: novobiocin, D-cycloserine, the penicillins, bacitracin, and vancomycin (126, 234a). However, although the
final result is the same in all cases, the mechanisms involved are greatly
different: the antibiotics in some way prevent the biosynthesis of the
wall, whereas the enzymes destroy, or impair the mechanical resistance
of, an already existing wall. As a consequence, the latter are able to
dissolve resting, or even killed, bacteria, whereas the former act only
upon metabolically active organisms, their effect resulting precisely from
the unbalanced growth for which they are responsible.
Another enzyme which can exert antibiotic effects is notatin, a flavoprotein with glucose oxidase activity, produced by Penicillium notatum,
P. vitale (234b), and other species. It is indirectly bactericidal through
its ability to produce the toxic hydrogen peroxide. The same kind of
antibiotic effect was reported for xanthine oxidase in the presence of
xanthine.
Antagonistic relations observed between mouth microorganisms and
the antibiotic activity of pneumococci have been explained by a similar
mechanism.
In closing this section, it should be recalled that several proteins from