What does units/mg mean for Streptavidin I got streptavidin for surface reaction. The label says "biotin binding: 16 units/mg". What does `units/mg` mean? Does it mean "1 mg biotin can bind to 16 units SA"? How much is the `unit` here?

16 units/mg means 16 units per milligram of protein.

Many companies, including Invitrogen, define 1 unit streptavidin as **the amount of streptavidin necessary to bind 1 microgram of biotin**.