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An Examination of Methods Used to Assay Potato Tuber Invertase and Its Naturally Occurring Inhibitor ¹

^a Department of Vegetable Crops, Cornell University, Ithaca, New York 14850

Confirming an earlier report, it was shown that the endogenous inhibitor of potato tuber invertase forms an essentially undissociable complex with the enzyme. Consequently, several previous analyses of potato tuber invertase which were based on equations derived for highly dissociable enzyme-inhibitor complexes are presumed to be in serious error. The complex formation proceeded slowly, requiring approximately 1 day to reach completion at 2 C, and 1 hr at 37 C. Allowing complex formation to reach completion before assaying enzyme activity did not affect the noncompetitive nature of the inhibition.

Contrary to previous reports that inhibitor could be selectively inactivated through foaming in a blender, both enzyme and inhibitor appeared to be denatured by such treatment. Foaming accomplished by passing nitrogen gas bubbles through extracts gave more favorable results.

¹ Supported by Hatch funds granted to Cornell University. Paper 611 of the Department of Vegetable Crops, Cornell University.