even lend a hand in the synthesis of drugs
and supplements such as vitamin E.
But enzyme-driven processes these
days can get much more involved than
just throwing starting materials into
an animal gut. Often materials need to
undergo additional reactions, treatment
with a solvent or dyeing with a chemical, before or after an enzyme can do its
job. For many of these reactions, heat is
required as a catalyst.
The problem: Most known enzymes
work only at conditions matching those
of the organism from which they came.
So temperatures have to be repeatedly
ramped up and lowered at various stages
of a multistep process. “You have to cool
it down for the biological part and heat
it back up for the next step,” says Vicki
Thompson of Idaho National Labora-
tory in Idaho Falls. “That makes the
process more expensive, and it’s waste-
ful of energy.”
During low-temperature stages, mate-
rials can also be vulnerable to attack
from a plethora of microbes.
The breakdown of long chains of glucose molecules from plants, or cellulose,
faces such troubles. Cellulose stored in
corn stover — the grassy part of corn that
people don’t eat and a potential biofuel
source — is tied up in complex chemical arrangements, making it hard for
enzymes working alone to get access.
So the biomass has to be mashed up
a bit first. It’s heated and treated with
corrosive chemicals like acids or salty
solutions, which expose the cellulose.
But the plant products have to be neutralized and cooled before a collection of
room-temperature enzymes can digest
the material into usable sugars.
Cellulose-breaking enzymes, called
cellulases, made by organisms that normally thrive under extreme conditions,
in places like hot springs or hydrothermal vents, could offer a solution.
“You can take those enzymes and use
them under the industrial conditions
that you are interested in,” explains
Thompson, who has been studying
organisms that live in extreme environments and the proteins they make for
more than a decade.
Biologist Thomas Brock unearthed one
of the first known extremophiles from
hot pools in Yellowstone National Park
in Wyoming in the 1960s. Later named
Thermus aquaticus, the bacterium
thrived best at temperatures around
70° C. This finding suggested life could
exist in all kinds of places that were previously thought of as dead zones.
Explorations in volcanic soil, hot
vents, deep seas and salt deserts have
turned up thousands of extremophiles
since, says Thompson. A sizable portion
love the heat. Notably, a heat-loving,
DNA-building enzyme from T. aquaticus
has been a major boon for genetic engineering and forensics. To analyze DNA
from collected samples, scientists need
large amounts of uncontaminated copies. By simply adding the enzyme, Taq
polymerase, to a starting strand of DNA
and other genetic ingredients, scientists
can make lots of DNA copies with no
contamination to worry about.
Over the last two decades, Frank Robb
of the University of Maryland, Baltimore
has scoured some of the hottest corners
of the Earth — from the hot springs at
Yellowstone to the deep-sea vents of the
Okinawa Trough — in search of interesting heat-loving enzymes. An ability
to break down cellulose is one sought-after skill in the “help wanted” ads.
Robb and Graham want cellulases
that can do their thing at temperatures
of 100° C or even higher. The more
types the better, since some enzymes
specialize in cutting the cellulose into
chunks and some break it down even
further into glucose.
Fueled by heat From a
hot pool in Nevada (above),
researchers pulled a cellulose-busting enzyme called EBI-244.
The enzyme shows its maximum
breakdown activity above 100°
Celsius (right), making it a good
candidate for use in biofuel
EBI-244 activity vs. temperature
Activity (micromole glucose/min/mg)
60 70 95 100
120 115 110 105 90 85 80 75 65