190
JAMES K. GRANT
It is tempting to speculate that cholesterol is a precursor of hormones
required by the insect during the larval stage or during metamorphosis,
and this might be thought to gain support from the observation (127)
that in the larva of the meal worm (Tenebrio molitor) the cholesterol
requirement decreases with age. However, an alternative explanation of
this observation is possible and experimental proof of the transformation
of cholesterol into other biologically active substances in insects is
lacking.
C. MICROBIOLOGICAL TRANSFORMATION OF STEROIDS
Bile acids, sterols of dietary origin or in the bile, and the metabolites
of steroid hormones excreted in the bile are exposed to the action of
bacteria in the intestines. The transformations of bile acids by these
bacteria have already been referred to (Section I,C,4). Cholesterol is
reduced to coprostanol in the intestines (128). Estrone and metabolites
of progesterone, testosterone (129), and hydrocortisone (130) have been
found in the bile of the ox and of human subjects, but nothing is known
of the possible microbiological transformation of these steroids in the
intestines. The presence of an enterohepatic circulation of steroids in
man was demonstrated by experiments in which C
14 -labeled estrone
was administered intravenously when about 80% of the C
14 appeared in
the urine. When bile was collected from a fistula, 50% of the C
14 appeared in the bile but in nonfistula subjects only about 7% of the C
14
was recovered from the feces (131). Thus the possibility exists that
steroids found in the urine may have been formed by bacteria in the
intestines. No systematic study of the steroids in feces has been made,
but it has been observed that the androgenic steroids in dried feces of
pregnant cows increase in amount on administration of progesterone to
the animals (132). The following substances have been identified in this
material: 5a- and 5/?-androstane-3,17-dione, androst-4-ene-3,17-dione, and
androst-l,4-diene-3,17-dione (133). The occurrence of the last compound
as a product of the action of a species of Fusarium on progesterone (134)
suggests that some of these androgens may be formed by microorganisms
in the intestines of the cow.
In addition to the intestinal flora, other bacteria and molds have been
found to effect transformations of steroids completely foreign to their
normal environment (135). The enzymes involved are probably induced
in the microorganisms, perhaps as a defense against intoxication. By
continued exposure of the organism to steroid, high activity of these
enzymes may be built up, and microbiological transformation of steroids
has become of considerable commercial importance. The reactions catalyzed include hydroxylations, other oxidations and reductions, some of
JAMES K. GRANT
It is tempting to speculate that cholesterol is a precursor of hormones
required by the insect during the larval stage or during metamorphosis,
and this might be thought to gain support from the observation (127)
that in the larva of the meal worm (Tenebrio molitor) the cholesterol
requirement decreases with age. However, an alternative explanation of
this observation is possible and experimental proof of the transformation
of cholesterol into other biologically active substances in insects is
lacking.
C. MICROBIOLOGICAL TRANSFORMATION OF STEROIDS
Bile acids, sterols of dietary origin or in the bile, and the metabolites
of steroid hormones excreted in the bile are exposed to the action of
bacteria in the intestines. The transformations of bile acids by these
bacteria have already been referred to (Section I,C,4). Cholesterol is
reduced to coprostanol in the intestines (128). Estrone and metabolites
of progesterone, testosterone (129), and hydrocortisone (130) have been
found in the bile of the ox and of human subjects, but nothing is known
of the possible microbiological transformation of these steroids in the
intestines. The presence of an enterohepatic circulation of steroids in
man was demonstrated by experiments in which C
14 -labeled estrone
was administered intravenously when about 80% of the C
14 appeared in
the urine. When bile was collected from a fistula, 50% of the C
14 appeared in the bile but in nonfistula subjects only about 7% of the C
14
was recovered from the feces (131). Thus the possibility exists that
steroids found in the urine may have been formed by bacteria in the
intestines. No systematic study of the steroids in feces has been made,
but it has been observed that the androgenic steroids in dried feces of
pregnant cows increase in amount on administration of progesterone to
the animals (132). The following substances have been identified in this
material: 5a- and 5/?-androstane-3,17-dione, androst-4-ene-3,17-dione, and
androst-l,4-diene-3,17-dione (133). The occurrence of the last compound
as a product of the action of a species of Fusarium on progesterone (134)
suggests that some of these androgens may be formed by microorganisms
in the intestines of the cow.
In addition to the intestinal flora, other bacteria and molds have been
found to effect transformations of steroids completely foreign to their
normal environment (135). The enzymes involved are probably induced
in the microorganisms, perhaps as a defense against intoxication. By
continued exposure of the organism to steroid, high activity of these
enzymes may be built up, and microbiological transformation of steroids
has become of considerable commercial importance. The reactions catalyzed include hydroxylations, other oxidations and reductions, some of