抄録
The chromogenic method for amylase activity using blue starch is widely used in clinical laboratories. This method is simpler, quicker and more reproducible than the amyloclastic method using iodine staining or the saccharogenic method using dinitrosalicylic acid. Recently, Levitt et al, found that the chromogenic method often showed considerably lower value on urinary amylase than the amyloclastic and saccharogenic methods. This discrepancy of amylase values was clearly improved by the addition of albumin or other proteins to reaction mixture. Among four proteins tested, albumin, . γ-globulin, α-casein and submaxillary mucin, albumin was most effective for the improvement of assay value.
The four proteins tested did not affect the Km value for a substrate, blue starch, appreciably, indicating that they did not affect the affinity of amylase for its substrate. But they did increase the Vmax value, showing that they increased the effective amount of amylase during incubation. Thus they will increase amylase activity by protecting the enzyme from inactivation.
Amylase activity was higher in urine samples containing proteins than in those without any protein. Therefore, amylase activity in urine samples showing proteinuria may be evaluated as higher than that in urine samples without detectable protein. Thus albumin should be added to the reaction mixture for assay of urinary amylase at a final concentration of 1mg/ml. The results also indicate that albumin should be added at the step of dilution of enzyme. Routine addition of albumin at these steps should make the assay more reliable for clinical purpose.
