3. LIPIDS: STEROID METABOLISM
189
acids with a calcified skeleton, and perhaps connect them with the
needs for exogenous antirachitic factors, the development of parathyroid glands, and the beginning of a special cholesterol metabolism
based on its endogenous synthesis and correlate these steps in biochemical evolution even with remoter points such as the increased resistance to lead poisoning or susceptibility to certain tumorous
growths."
II. The Metabolism of Steroids
A. INTRODUCTION
The complexity of the metabolism of steroids in higher animals is
readily appreciated. The steroid hormones and their metabolites alone
account for almost two hundred substances isolated from animal tissues
and excreta. The diversity of products which may be obtained from a
single relatively simple steroid is indicated by the detection of fifty-five
distinct substances on incubation of 4-C
14 -androst-4-ene-3,17-dione with
ox adrenal homogenates (122). By contrast almost nothing is known of
the metabolism of steroids by insects which usually show a nutritional
requirement for sterols or by plants and microorganisms which either
synthesize these substances or encounter them naturally in their environment. The recently revived interest in the transformation of steroids
by microorganisms which may never naturally encounter these substances has indicated the possibility of effecting a wide range of steroid
reactions and of preparing many steroids not so far found in animal
tissues. These transformations are however not strictly speaking metabolic reactions. Although much has been learned about the occurrence
of sterols in invertebrates* nothing is known of their metabolism in
these animals.
B. METABOLISM OF STEROLS BY INSECTS
The nutritional requirement of insects for sterols has recently been
reviewed (123). Free or ester cholesterol is effective in supporting
normal growth in many insects and thus it is not surprising that
esterase has been reported in the intestines of the wax moth Galleria
mellonelL· (124) and the American cockroach Periphneta americana
(125). Evidence was also obtained that the latter insect can degrade
the side chain of the cholesterol molecule. The Australian ant Iridomyrmex delectus contains cholesterol and is known to produce methylheptenone (126). As pointed out by Horning (123), this could be
readily obtained from the cholesterol side chain at C-17.
* See Chapter 2 in this volume by W. Bergmann.
189
acids with a calcified skeleton, and perhaps connect them with the
needs for exogenous antirachitic factors, the development of parathyroid glands, and the beginning of a special cholesterol metabolism
based on its endogenous synthesis and correlate these steps in biochemical evolution even with remoter points such as the increased resistance to lead poisoning or susceptibility to certain tumorous
growths."
II. The Metabolism of Steroids
A. INTRODUCTION
The complexity of the metabolism of steroids in higher animals is
readily appreciated. The steroid hormones and their metabolites alone
account for almost two hundred substances isolated from animal tissues
and excreta. The diversity of products which may be obtained from a
single relatively simple steroid is indicated by the detection of fifty-five
distinct substances on incubation of 4-C
14 -androst-4-ene-3,17-dione with
ox adrenal homogenates (122). By contrast almost nothing is known of
the metabolism of steroids by insects which usually show a nutritional
requirement for sterols or by plants and microorganisms which either
synthesize these substances or encounter them naturally in their environment. The recently revived interest in the transformation of steroids
by microorganisms which may never naturally encounter these substances has indicated the possibility of effecting a wide range of steroid
reactions and of preparing many steroids not so far found in animal
tissues. These transformations are however not strictly speaking metabolic reactions. Although much has been learned about the occurrence
of sterols in invertebrates* nothing is known of their metabolism in
these animals.
B. METABOLISM OF STEROLS BY INSECTS
The nutritional requirement of insects for sterols has recently been
reviewed (123). Free or ester cholesterol is effective in supporting
normal growth in many insects and thus it is not surprising that
esterase has been reported in the intestines of the wax moth Galleria
mellonelL· (124) and the American cockroach Periphneta americana
(125). Evidence was also obtained that the latter insect can degrade
the side chain of the cholesterol molecule. The Australian ant Iridomyrmex delectus contains cholesterol and is known to produce methylheptenone (126). As pointed out by Horning (123), this could be
readily obtained from the cholesterol side chain at C-17.
* See Chapter 2 in this volume by W. Bergmann.