Por que purificar proteinas

‘‘Don’t waste clean thinking on dirty enzymes’’ is an admonition of
Efraim Racker’s which is at the core of enzymology and good chemical
practice. It simply says that detailed studies of how anenzyme catalyzes the
conversion of one substance to another is generally a waste of time until the
enzyme has been purified away from the other enzymes and substances that
make up a crude cellextract. The mixture of thousands of different enzymes
released from a disrupted liver, yeast, or bacterial cell likely contains several
that direct other rearrangement of the starting material and theproduct of
the particular enzyme’s action. Only when we have purified the enzyme to
the point that no other enzymes can be detected can we fell assured that
a single type of enzyme molecule directsthe conversion of substance A
to substance B, and does nothing more. Only then can we learn how the
enzyme does its work.
The rewards for the labor of purifying an enzyme were laid out in a seriesof inspirational papers by Otto Warburg in the 1930s. From his laboratory in
Berlin-Dahlem came the discipline and many of the methods of purifying
enzymes and with those the clarification of keyreactions and vitamin functions
in respiration and the fermentation of glucose. Warburg’s contributions
strengthened the classic approach to enzymology inaugurated with Eduard
Bu¨chner’s accidentaldiscovery, at the turn of this century, of cell-free
conversion of sucrose to ethanol. One tracks the molecular basis of cellular
function—alcoholic fermentation in yeast, glycolysis in muscle,luminescence
in a fly, or the replication of DNA—by first observing the phenomenon
in a cell-free system. Then one isolates the responsible enzyme
(or enzymes) by fractionation of the cell extract andpurifies it to homogeneity.
Then one hopes to learn enough about the structure of the enzyme to
explain how it performs its catalytic functions, responds to regulatory signals,
and is associated...