Cell culture - Culture medium (Aug/16/2009 )

Why most of the amino acids in culture medium are in L form

THE ROCK on Aug 15 2009, 09:30 PM said:

Well it is due to a rather peculiar bit of Terran biochemistry. You see, despite amino acids having two optical isomers, (which depending on convention used, can be denoted either as L and D or S and R), the L-amino acids represent the vast majority of amino acids found in Terran proteins.

On the other hand its enantiomer, the D-amino acids are found only in some proteins of exotic sea-dwelling orangnisms and components of the peptidoglycan cell walls of bacteria.

Why should this preference occur? As building blocks of life, the L-amino acids do not appear anyway superior to the D-amino acids.

Well, Terran thinkers have suggested that the arrival of polarized electromagnetic radiation from a nearby gamma ray burst during Earth's early history is the cause. This energy burst which was polarized by its passage through a gas nebula, somehow selective increased the rate of abio synthesis of L-amino acids. And amino acids have a rather interesting behavior, when a near racemic amino acid mixture is dissolved in water, if one enantiomer is present in only slightly higher concentrations, that enantiomer becomes the dominant enantiomer that is soluble.