Deamidation of glutamine by increased plasma gamma-glutamyltransferase is a source of rapid ammonia formation in blood and plasma specimens.
Owing to increased enzymatic hydrolysis of glutamine, additional ammonia is formed in blood and plasma specimens with increased gamma-glutamyltransferase activity (gamma-GT, EC 2.3.2.2.). The close correlation between gamma-GT and glutaminase (EC 3.5.1.2) activities (r = 0.97) in plasma, the inhibition with 6-diazo-5-oxo-L-norleucin or borate plus serine, and the activation with maleate clearly show that gamma-GT itself is the glutamine-deamidating enzyme in plasma. Under pathological conditions, increased gamma-GT activity can increase the rate of ammonia formation in plasma more than 30-fold the mean values of healthy subjects. Increased in vitro formation of ammonia caused by increased gamma-GT activity is an important source of false-positive findings in ammonia determination. Because of the high prevalence of pathological gamma-GT activities in clinical populations, blood specimens for ammonia analysis should be preserved by addition of borate plus serine.
da Fonseca-Wollheim
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Central Laboratory Department, Behring-Krankenhaus Berlin-Zehlendorf, F.R.G.
D000641:Ammonia / Q000097:blood*; D001881:Borates / Q000494:pharmacology; D002850:Chromatography, Gel; D003980:Diazooxonorleucine / Q000494:pharmacology; D005189:False Positive Reactions; D005971:Glutamates / Q000097:blood; D018698:Glutamic Acid; D005972:Glutaminase / Q000037:antagonists & inhibitors / Q000097:blood; D005973:Glutamine / Q000378:metabolism*; D006801:Humans; D008298:Maleates / Q000494:pharmacology; D012694:Serine / Q000494:pharmacology; D013048:Specimen Handling; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors / Q000097:blood*
D001881:Borates; D005971:Glutamates; D008298:Maleates; D003980:Diazooxonorleucine; D005973:Glutamine; D018698:Glutamic Acid; D012694:Serine; D000641:Ammonia; C030272:maleic acid; D005723:gamma-Glutamyltransferase; D005972:Glutaminase