Well, I'm using catechin for my polyphenol oxidase assay to determine the substrate specificity. But the problem is when I try to use 50mM above, the concentration seems to be very high which the spectrophotometer shows more than 4.500. What should I do?? I couldn find any info from the website or journals. Should I dilute it? And I should dilute the substrate only or together with the enzyme? The total volume is 2.9ml, so if i dilute it using 1:2 ratio, means 2ml of buffer and 1ml of substrate? The total volume of blank is 3.0ml of buffer + substrate. Please help me ! Thanks a lot !!