Which is the appropriate coenzyme for the measurement of ammonia with glutamate dehydrogenase?
The determination of ammonia in plasma, using glutamate dehydrogenase, is complicated by non-specific oxidation of the coenzyme, promoted by components of the sample matrix. Measurements performed with appropriate plasma blanks show that 2'-phosphorylated coenzymes (NADPH, deamino-NADPH) are much less oxidized than NADH. By adding lactate dehydrogenase, NADH oxidation by endogenous pyruvate can be completed within a short time. Considerable consumption of coenzyme occurs, however, and endogenous L-alanine aminotransferase also represents a possible source of interference. The results of ammonia determinations using deamino-NADPH (y) or NADPH (x) were identical (a = 0.0 mumol/l, b = 1.00; r = 0.996, n = 62). With NADH as the coenzyme, the method displays adequate specificity only at high sample dilution, e.g. in the measurement of urea after conversion to ammonia.
da Fonseca-Wollheim
F
F
Zentrallaboratorium, Behring-Krankenhaus Berlin-Zehlendorf.
Heinze
K G
KG
D000641:Ammonia / Q000097:blood*; D003067:Coenzymes / Q000097:blood*; D005969:Glutamate Dehydrogenase / Q000097:blood*; D006801:Humans; D009243:NAD / Q000097:blood; D009249:NADP / Q000097:blood; D010084:Oxidation-Reduction; D012680:Sensitivity and Specificity; D013053:Spectrophotometry
D003067:Coenzymes; D009243:NAD; D009249:NADP; D000641:Ammonia; D005969:Glutamate Dehydrogenase