504
MARY BELLE ALLEN
filtrates was lost during heating for one hour at 60°. Pringsheim (154,
155) studied a cellulase from thermophilic cellulose-fermenting bacteria
which hydrolyzed cellulose to cellobiose over the temperature range
20-70°. These findings lent support to the view that the proteins of
thermophilic microorganisms must be in some way modified so that
they are not destroyed by the high temperatures at which the organisms
grow. Recently Sobotka et al. (166) have studied the extracellular proteins produced by some thermophilic bacteria and found them to be resistant to thermal denaturation. It is of special interest that the protein
from organisms grown at 75° contained an amino acid component not
present in protein formed by cells growing at lower temperatures.
As knowledge of enzymes and microbial biochemistry increased, it
became evident that extracellular hydrolytic enzymes need not be good
indicators of the thermostability of the essential intracellular proteins of
microorganisms. Attention then turned to the respiratory enzymes and
other cellular proteins. Militzer and his co-workers (183-187) have
furnished good evidence for the existence of thermostable respiratory
enzymes in a stenothermal thermophilic bacterium. This group has obtained thermostable cell-free preparations of malic dehydrogenäse, cytochrome oxidase, cytochrome b, cytochrome c, succinoxidase, aldolase,
and apyrase. Most of these enzymes are found together in a particulate
"red fraction" which appears to constitute a morphological entity within
the cell, but a soluble apyrase has been prepared, indicating that combination in a particle is not necessary for thermostability of the proteins
from their bacterium.
Koffler and his collaborators (188-190) have shown that the total
cytoplasmic protein and the flagella from some thermophilic bacteria are
more heat stable than similar preparations from bacteria growing at
lower temperatures. Flagella from thermophils also showed an increased
resistance to urea, acetamide, and detergents, indicating more "effective"
hydrogen bonding in proteins from the organisms living at high temperatures. This work is of interest in that it provides the first indication of
how proteins from thermophilic bacteria might be rendered more
thermostable, and perhaps also gives a clue as to the reason for the inability of stenothermal thermophils (the bacteria in which notably heat
resistant proteins have been demonstrated are generally stenothermal,
see below) to grow at ordinary temperatures. The greater rigidity given
to their proteins by a greater degree of hydrogen bonding may render
them unable to carry out their normal catalytic functions until a greater
than usual thermal energy is provided. However, individual enzymes of
stenothermal thermophils can function at ordinary temperatures.
Reactions of enzyme inactivation and protein denaturation are char-
MARY BELLE ALLEN
filtrates was lost during heating for one hour at 60°. Pringsheim (154,
155) studied a cellulase from thermophilic cellulose-fermenting bacteria
which hydrolyzed cellulose to cellobiose over the temperature range
20-70°. These findings lent support to the view that the proteins of
thermophilic microorganisms must be in some way modified so that
they are not destroyed by the high temperatures at which the organisms
grow. Recently Sobotka et al. (166) have studied the extracellular proteins produced by some thermophilic bacteria and found them to be resistant to thermal denaturation. It is of special interest that the protein
from organisms grown at 75° contained an amino acid component not
present in protein formed by cells growing at lower temperatures.
As knowledge of enzymes and microbial biochemistry increased, it
became evident that extracellular hydrolytic enzymes need not be good
indicators of the thermostability of the essential intracellular proteins of
microorganisms. Attention then turned to the respiratory enzymes and
other cellular proteins. Militzer and his co-workers (183-187) have
furnished good evidence for the existence of thermostable respiratory
enzymes in a stenothermal thermophilic bacterium. This group has obtained thermostable cell-free preparations of malic dehydrogenäse, cytochrome oxidase, cytochrome b, cytochrome c, succinoxidase, aldolase,
and apyrase. Most of these enzymes are found together in a particulate
"red fraction" which appears to constitute a morphological entity within
the cell, but a soluble apyrase has been prepared, indicating that combination in a particle is not necessary for thermostability of the proteins
from their bacterium.
Koffler and his collaborators (188-190) have shown that the total
cytoplasmic protein and the flagella from some thermophilic bacteria are
more heat stable than similar preparations from bacteria growing at
lower temperatures. Flagella from thermophils also showed an increased
resistance to urea, acetamide, and detergents, indicating more "effective"
hydrogen bonding in proteins from the organisms living at high temperatures. This work is of interest in that it provides the first indication of
how proteins from thermophilic bacteria might be rendered more
thermostable, and perhaps also gives a clue as to the reason for the inability of stenothermal thermophils (the bacteria in which notably heat
resistant proteins have been demonstrated are generally stenothermal,
see below) to grow at ordinary temperatures. The greater rigidity given
to their proteins by a greater degree of hydrogen bonding may render
them unable to carry out their normal catalytic functions until a greater
than usual thermal energy is provided. However, individual enzymes of
stenothermal thermophils can function at ordinary temperatures.
Reactions of enzyme inactivation and protein denaturation are char-