chemistry. In 1951 he retired from the Mayo Founda-
tion and accepted the position of visiting professor in
the department of biochemistry at Princeton University.
In 1914 he isolated thyroxine, the active principle
of the thyroid gland, and also discovered the crystal-
lization and chemical nature of glutathione, and con-
ducted work on the oxidation systems in animals.
Kendall isolated and identified a series of com-
pounds from the adrenal gland cortex, and while work-
ing at Merk & Co., Inc., he prepared cortisone by
partial synthesis. He also investigated the effects of cor-
tisone and of adrenocorticotropic hormone (ACTH) on
rheumatoid arthritis with Philip S. HENCH, H. F. Polley,
and C. H. Slocumb. Kendall and Hench, along with
Tadeus REICHSTEIN, shared the Nobel Prize in physiolo-
gy or medicine in 1950 for this work. Kendall received
many awards and honors. He died on May 4, 1972.
keratin A tough, insoluble, fibrous protein with
high sulfur content that forms the main structure
and protective barrier or cytoskeleton of epidermal
cells and is the chief constituent of skin, hair, nails,
and enamel of the teeth. It is produced by ker-
atinocytes, the most abundant cells in the epidermis
(95 percent). Keratin makes up 30 percent of the cel-
lular protein of all living epidermal cells. The high
amount of sulfur content is due to the presence of the
amino acid cystine.keystone predator Adominant species as predator
that maintains species richness in a community through
selective predation of the best competitors in the com-
munity, and as a result maintains populations of less
competitive species.186 keratin
12 3 4 56 7 8 9 10 11 1213 14 15 16 17 1819 20 21 22 X/YThe term karyotyperefers to the chromosomal complement of an individual, including the number of chromosomes and any abnormalities.
Theterm is also used to refer to a photograph of an individual’s chromosomes.(Courtesy Darryl Leja, NHGRI, National Institutes of Health)