Stability of Glutamic Acid, Glutamine, and gamma-Glutamyl Derivatives during Isolation from Natural Sources.

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Abstract
14C-Labeled glutamic acid, glutamine, alanine, 5-oxoproline and .gamma.-glutamylalanine (in different experiments labeled in the different amino acid moieties) were subjected to ion-exchange fractionations either in mixtures with pure amino acids or in mixture with an extract from seeds of Fagus silvatica containing large amounts of .gamma.-glutamyl derivatives. Limited degradation of glutamine into glutamic acid and 5-oxoproline was observed. When glutamic acid is applied in aqueous ethanol to a strongly acidic ion-exchange resin in the hydrogen form with subsequent elution with ammonia, partial transformation via the .gamma.-ethyl ester to 5-oxoproline takes place. No production of .gamma.-glutamyl derivatives by ring-opening of 5-oxoproline by transpeptidation takes place. Apparently .gamma.-glutamyl derivatives cannot be produced chemically as artifacts during standard procedures for isolation of amino acids from natural material.

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