1955, Alex Novikoff of the 
Albert Einstein College of 
Medicine clearly identified 
some lysosomes in rat liver 
cells, and it is now known 
that lysosomes (whose name 
refers to the fact that their 
enzymes can lyse, or digest, 
substances) exist in all 
eukaryotic cells. In fact, lyso- 
somes contain over 40 
different enzymes that can 
digest almost anything in the 
cell, including proteins, RNA, 
DNA, and carbohydrates. 
At about the same time that 
de Duve and his colleagues 
were describing the bio- 
chemistry of lysosomes, they 
detected another enzyme-con- 
taining organelle. In 1965, de 
Duve proposed that the 
organelle be called a peroxi- 
some because it appeared to 
both generate and break down 
hydrogen peroxide, a corrosive 
molecule composed of two 
atoms each of hydrogen and 
oxygen. 
Today it is known that 
peroxisomes exist in most 
eukaryotic cells, and that 
they are especially prominent 
in mammalian liver cells. The 
membrane that surrounds a 
peroxisome is usually 
permeable, permitting many 
small molecules to enter easily. 
Peroxisomal enzymes remove 
hydrogen atoms from these 
small molecules and join the 
hydrogen to atoms of oxygen to 
form hydrogen peroxide. One 
of the peroxisomal enzymes, 
catalase, then neutralizes the 
hydrogen peroxide by cat- 
alyzing its breakdown into 
water and oxygen. This two- 
step process is the method 
that peroxisomes in the liver 
use to break down molecules 
of alcohol into substances that 
can be eliminated from the 
body. About one-quarter of the 
alcohol that enters the liver is 
processed in peroxisomes. 
In his early descriptions of 
peroxisomes, de Duve called 
them “fossil organelles” 
because of their primitive 
nature and seemingly 
expendable actions. (All of 
the enzymes found in peroxi- 
somes are also found 
33 
