The L (Leva, Greek for "left") and D (Dextro, Greek for "right")
forms of amino acids are isomers of each other.  They are
compounds with identical chemical formulas, but in one case
a particular functional group within the molecule is found on
the left side when viewed in a certain orientation and in the
other case the same functional group appears on the right
side when viewed in the same orientation.

According to my organic chemistry book, almost all of the
amino acids found in humans and other living organisms are
the L form.  So it's the L form that you want.

It may well be that when you buy something sold as just
"Glutamine", it's also the L form.  That's the form that's going
to be derived by processing beans or cabbage, or whatever
they process to get it.  It may actually be the only form you
can buy even if it's not labeled that way.

I imagine that most of the companies that sell supplements
don't really know what they're selling.  Some of them probably
buy chemicals in bulk and put them in pills.  Some probably
don't even do that, they just buy them in pills, maybe even in
bottles, with the contractor putting the label on that's provided
by the seller.

I think it's always a good idea to buy from some sort of name
brand organization that you have reason to believe stands
behind what they sell and actually knows what's inside.  However
I'm not sure what the best way to find such sellers is.

   Alan