Imagine you're a cell.
Inside your body runs the machinery that creates life itself. But
as that machinery keeps running, day after day, you begin to get worn
out - the friction and the processes that cause damage (here the
"free-radicals" - highly destructive little entities generated by
biochemical processes, as well as pollutants, UV radiation and other
sources) start to create havoc and you begin to lose the battle to
disease, old age and ultimately death.
In fact your battle would
be over much sooner were it not for the numerous mechanisms that you and
other mammalian cells evolved over millions of years, as protection from
the injury that can result from your normal functional processes. The
foremost among these internal protective systems is the "Glutathione
antioxidant system."
Glutathione, a small molecule composed
of three amino acids - glycine, glutamate and cysteine
- acts as your cellular Super-Mop, soaking up "free-radicals" (with the
help of the sulfur-containing portion of the cysteine molecule),
protecting your cellular membranes and internal organs from the
cascading destruction they can cause. 
Besides being the major antioxidant that you produce as
protection from "free-radicals," glutathione is also a very important
detoxifying agent, enabling you to get rid of undesirable toxins
and pollutants. If you were a liver, kidney or lung cell, you
would contain high levels of glutathione, as you'd be exposed to
the greatest levels of toxins.
Glutathione also helps you dispose of many cancer-producing
chemicals, heavy metals, drug metabolites etc. that invade the pristine
recesses of your cellular world. And Mother Nature (the first recycler)
also designed you to use glutathione to recycle other well-known
antioxidants such as vitamin C and vitamin E, keeping them in their
active state.
If you were a cell delegated to the immune system department, you
would require glutathione for many of the intricate steps needed to
carry out your essential immune response functions - such as
multiplying to make many clones of yourself, to mount a full-bodied
immune response, or "neutralizing" undesirable elements of the cellular
community, like cancerous or virally infected cells.
But your finicky cell membrane does not allow whole glutathione
molecules to cross over directly into your cellular spaces. And every
time a molecule of glutathione neutralizes a destructive free-radical or
toxin, it fatally binds with the undesirable element and is washed out
with them in the bile or the urine.
So how do you replenish your stores and get your daily fix
of glutathione? Simple. You manufacture it in your cellular factory,
from its raw materials - glycine, glutamate and cystine (a cysteine=cysteine dipeptide - consisting of two
molecules of cysteine
joined together). Cystine enters the blood
with no digestion, and donates two cysteine
molecules in the cells, where they're used to create glutathione.
If your human eats a diet
high in fresh fruits and vegetables and freshly prepared meats, you
should get be getting enough glutamate and glycine.
But cystine comes mostly from eggs, milk
and cheese.
And when eggs, milk and cheese are cooked or
processed, the heat breaks down the dipeptides of cystine to
cysteine. While still a valuable amino
acid, it can no longer feed your glutathione levels.
If you can get a sufficient supply of cystine (which determines the rate at which you
can make glutathione), your arsenal is well-stocked. If not, you and
your human are at a strategic disadvantage in the battle of "Cell v/s
Free-radical Destroyers."
As a normal, healthy cell, increasing your glutathione levels
could help you and your human maintain that strategic advantage
in the battle against free-radicals. If you're not really in your prime,
boosting your levels could tip the scales in your favor, and help you
fight the cellular damage that causes disease and
aging.
So how do you get your daily diet of glutathione
precursors? Find out in your Free Wellness Report
Transport of glutathione, as g-glutamy l-cysteinylglycyl ester,
into liver and kidney. Puri RN, Meister A.
[Proc Natl Acad Sci USA 80: 5258-60, 1983]
Glutathione
monoethylester: Preparation, uptake by tissues, and conversion to
glutathione. Anderson ME, Powric F,Puri RN, Meister.A. [Arch
Biochem Biophys 239: 538-48, 1985.]