The products of invertase are reducing sugars. sucrose is hydrolyzed to glucose and fructose with the latter being strongly reducing. You can test for the reducing products crudely by using hot (90 C) 0.5 N NaOH in which 2,3,5-triphenyl-2H-tetrazolium chloride monohydrate (Tetrazolium red) is dissolved at 1 mg/ml just before doing the test. I.e take sucrose solution maybe 0.1 g per ml in 0.1 M sodium acetete buffer at pH 5.5. Incubate with extract containing invertase. Add a drop or two of above reagent then heat quickly in a microwave/ put in boiling bath. Take great care with the hot alkali. Best to let the stuff sit for a time. The dye is unstable over time but this is a quick and dirty screening method. If you can do electrophoresis demonstrations, the invertase activity can be stained on polyacrylamide gels using the above stain. Electrophoresis is usually done using a Tris buffer. After electrophoresis, the gels should be first soaked in two changes of buffer to remove Tris as this inhibits glycosidases, then soaked in a sucrose solution in suitable buffer. For yeasts this has be the acetate buffer mentioned above. After sucrose has been hydrolyzed, this requires some trial runs to establish typical times, the gel is then dropped into hot alkaline tetrazolium red solution and the fructose stains (Gabriel & Wang, 1969. Analytical Biochemistry 27:545-554). For more quantitative assays of invertase, use a glucose oxidase reagent to measure the amount of glucose released from sucrose. Remember alpha glucosidases also hydrolyse sucrose so appear to have an invertase activity. In my opinion, the term invertase is best restricted to those enzymes that are beta-fructofuranosidases. However, if you are dealing with alpha-glucosidases, assays are much easier. For example you can probably use nitrophenyl-alpha-D-glucoside as a substrate, adding 1 M sodium carbonate to stop/slow the reaction and maximize the color of the nitrophenol without cleaving the substrate. Is this what you needed? Or ideas of principles using invertase? Paul Lehmann Ph.D. Department of Microbiology Med Coll Ohio Toledo [log in to unmask]