2.Introduction of KAKENHI Projects
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Chemical studies on the red sweat of the
hippopotamus
Kimiko Hashimoto
Associate Professor
Kyoto Pharmaceutical University
【Background】
Some mammals produce colored secretion on their skin from various glands.
For example, hippopotamus secret red
sweat on the whole body surface and elephants discharge blue liquid from the temporal glands on the sides of the head. In
spite of the interesting phenomena, chemical studies of the colored principles had
not been performed. We focused on the
red sweat of the hippopotamus and isolated two unstable pigments, called hipposudoric acid (red) and norhipposudoric acid
(orange), as the responsible compounds to
the red coloration (Nature, 2004). According to the ancient tradition on the roles of
the red sweat for the animal, it is useful to
protect the skin from harmful UV light
and also prevent infection of microbes
from the injured skin. We revealed that
the isolated pigments must be medicines
by absorbing UV light and also by having
antibiotic properties.
【Results】
In fact hippopotamus secretion is originally colorless and it becomes reddish within
a few minutes after perspiration. It finally
turns brown producing polymers of the
pigments within a few hours. We were interested in the mechanisms of the pigments formation. In order to isolate the
precursor of the pigments, we collected
the colorless sweat just after perspiration
and analyzed organic molecules of low
molecular mass. We found homogentisic
acid of reasonable content. Biogenetic
consideration of the hipposudoric acid
easily suggests that two molecules of homogentisic acid produce the red pigment
by an oxidative coupling. Then,“how are
they converted?” was the next problem.
Possible candidates oxidizing the homogentisic acid are oxygen, sunlight, microbe,
and enzyme. We found that an enzyme
contained in the sweat catalyzed this oxidation reaction using oxygen in the air.
Additionally, we also performed the chemical synthesis of these unstable pigments.
【Outlook】
One of the next challenges is the structure
determination of the brown polymers.
The synthetic pigments should be useful
not only for clarifying the polymer structure but also for functional properties and
the roles for the animal. Another subject
is elucidation of the structure and function of the unique enzyme. We hope that
these studies contribute to the progress in
chemistry and biology.
Fig. 1: The red sweat of the hippopotamus
Related Grants-in-Aid for Scientific Research:
FY2005-2007 Grant-in-Aid in Scientific Research (B):“Studies on the bioactive pigments isolated from mammalian secretions”
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