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]