Enzymes— The Catalysts of Life 
Without enzymes, there would be no life. 
Nearly all of the myriad chemical reactions 
occurring within a cell at any moment 
require the participation of at least 1 of the 
4,000 or so enzymes in the cell's reper- 
toire. Many cellular processes are energeti- 
cally unfavorable; without enzymes they 
would proceed slowly or not at all. 
Enzymes act as catalysts, speeding up 
reactions without being permanently altered 
themselves. Thus, enzymes can do their 
jobs — often, cutting apart or splicing 
together other molecules — over and over. 
According to chemist Ronald Breslow of 
Columbia University, enzymes work so well 
that a process that takes 5 seconds (such as 
reading this sentence) with enzymes would 
take 1 ,500 years without them. Enzymes 
also have great specificity; like a lock, each 
enzyme will accept only appropriately 
shaped "keys" (called substrates). 
With few exceptions, enzymes are 
proteins and are made of strings of amino 
acids ordered according to instructions 
contained in the genes. Even if the 
sequence of amino acids in an enzyme is 
known, however, scientists cannot predict 
how the enzyme will fold into its final, active 
shape. This is the so-called "folding 
problem" that many researchers are working 
to solve. If scientists can learn the rules by 
which enzymes and other proteins fold, it 
would open the way to synthesizing 
engineered, artificial enzymes with thera- 
peutic, industrial, and manufacturing 
applications. 
The first exception to the rule that all en- 
zymes are proteins was uncovered in the 
early 1 980's when Thomas Cech of the 
University of Colorado at Boulder and other 
scientists made the startling discovery that 
the nucleic acid RNA can act as an enzyme 
because it can cut and splice itself. This ob- 
servation, which led, in 1989, to a Nobel 
Prize for Cech and Sidney Altman of Yale 
University, has caused some scientists to 
speculate that RNA was the first self-forming 
and self-reproducing molecule to evolve. 
If an enzyme is missing or malfunctioning, 
one of a large class of diseases, collectively 
called metabolic disorders, may develop. 
To date, most attempts at treating such 
diseases in humans with enzyme replace- 
ment have failed because the body quickly 
breaks down ingested or injected enzymes. 
In 1 987, however, researchers at Duke 
University developed a chemically "camou- 
flaged" enzyme that can escape detection 
by the antibodies that attack foreign 
molecules. It has shown promise in treating 
children who are deficient in adenosine 
deaminase, an enzyme that plays a crucial 
role in the immune system. 
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