It depends on the assay kit you're using (as different kits may have different amounts of reagents). A standard abcam kit allows for 500 tests - this means that enough reagent is supplied for you to test for activity in 500 wells (of a 96 well plate). The amount of use you get out of the kit will also depend on the size of your experimental design, but I imagine it would do at least a few separate experiments.

almost about 500 reactions.

Kit information sheet should provide this info. If not, best call their toll free number since their technical service can guide you best since they made the kit.