Letter: Bichromatic analyses with the ABA-100--a critical assumption.

aAA ay with no add ed glutam ate repeated at end of experiment. bition at the lower (and suboptimal) substrate concentration used in this method.fect of glutamate on apparent serum-y-glu-tamyltranspeptidase activity. and-y-glutamyltranspeptidase activity. of significant effect of L(+)-glu-tamate on serum-y-glutamyltransferase activity det&rmined in the presence of glycyl-glycine. of-y-glutamyl-transpeptidase by reaction rate assay at 37 ence of increasing concentrations of L-glutamate. The final reaction mixture for the first method approximates the method used by Rock and Slickers , but was done at 37 #{176}C and con-tamed, per liter, 4 mmol of-y-glu-tamyl-p-nitroanilide (Sigma), 40 mmol of glycylglycine, and 185 mmol of tnis (hydroxymethyl) aminomethane buffer (pH 8.25). L-Glutamic acid (Sigma) was added to the buffer to give a final concentration in the reaction mixture ranging from 0 to 1.0 mmol/liter. The final reaction mixture had a sample/volume ratio of 1/29. The reaction was measured by mea-suning the rate of change of absorb-ance at 410 nm at 37 #{176}C, by use of an LKB Model 8600 reaction rate analyz-en, and the activity was calculated in U/liter. The final reaction mixture for the second method (5)-a method currently in use in this laboratory-con-tamed, per liter, 8 rnmol of 'y glu-tamyl-p-nitroanilide (Sigma), 67 mmol of glycylglycine, and 100 mmol of 2-amino-2-methylpropane-1,3-diol buffer (pH 8.30). The final reaction mixture had a sample/volume ratio of 1/12. Identical concentrations of L-glutamate were used as in the first method. Data collected during this study showed good precision, similar to that described previously (5), and a similar precision for both the first and second methods. Table 1 shows the mean results of triplicate determinations. The assays were performed in the order shown left to night in the Table, each set of results for a given patient being ob-tamed within the same analytical batch. A zero concentration of L-glu-tamate was analyzed at the beginning and end of each patient batch. These results are reported to one decimal place, but one should not infer that single-yGT determinations are this precise. The precision of these results is about 0.5 to 1.0 standard deviation units as a result of their being the mean of triplicate determinations. Comparison of activities with Stu-dent's t-test for pained observations did not show any significant activation (P > 0.1) by either of the two methods at any concentration of added gluta-mate. The first method showed a decrease in yGT activity at 0.5 mmol/ liter concentration of L-glutamate (0.05 < …