Keratin: That’s tough to chew

by Pat Kelley

When an animal dies outdoors, after about one month, all that is left of the poor creature is a pile of hair, skin, and bones. The reason that these parts remain is the simple fact that Mother Nature has very few participants willing and able to consume these materials. Keratin in the hair, skin, nails, hooves, horn, and the enamel on teeth make it extremely difficult to digest for nearly every species in our world.

Now get ready for a daily dose of science! Keratin is composed of polymers of amino acids making it an extremely stable and strong substance. Polymers are simply large chains of molecules composed of many similar smaller chains linked together (Think of chainmail armor). In the case of keratin, the most common chain is the amino acid called cysteine. Cysteine contains a high amount of sulfur and the disulfide bonds in cysteine are a key factor for keratin’s durability in nature. This is a big reason why it is difficult
to digest.

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Common keratin consuming insect pests (clockwise from top left): Varied carpet beetle, Webbing clothes moth, Black carpet beetle and Casemaking clothes moth

Just how difficult is keratin to ingest? Consider house cats and wild cats alike that constantly clean, lick, and ingest their fur. Even in the highly acidic digestive tracts of these predatory animals, their ingested hair does not break down. Instead it accumulates into hair balls that need to be coughed up or even removed for the health of the cat. This shows that keratin is one tough compound! Also, think about a time that you may have accidentally burned or singed your hair. The high amount of sulfur in keratin is the reason why singed hair smells strong to us.

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The high amount of sulfur in keratin is the reason why singed hair smells strong to us.

A few select insects have evolved to be able to break down keratin for their own benefit. The digestive tracts in the larvae of clothes moths and several species of carpet beetles have adapted to be able to disassemble the disulfide bonds in the keratin and utilize the protein in hair, skin, and other natural materials. In this sense, these insects are beneficial and, quite frankly, without this particular set of insects, we would have large numbers of partially decomposed animal carcasses lying all around the place. Mankind’s only real problem with these insects occurs when we want to preserve certain furs, hides, antlers or other keratin based material in our homes and museums. The same insects that help us in nature can be a curse in these locations.

Take a brief moment to soak in all of the specialized biological processes that go into breaking down these complex animal proteins. While you’re at it, get a haircut. Your keratin is getting long!

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