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Lactase has been partially purified from human intestinal mucosa. Lactase was inhibited by glucose, galactose, and fructose with the use of a radioisotopic assay; sucrase was inhibited by glucose and fructose; and maltase was inhibited by glucose alone. However, the Ki for glucose was the same (about 30 mM) for all 3 enzymes. No obvious structural requirements could be determined for inhibition of lactase, but naturally occurring sugars were the best inhibitors. inhibition by sugars of all disaccharidases was pH dependent, with a pH optimum of 6. It was suggested that inhibition of lactase by sugars might be physiologically important and provide one mechanism for the production of lactose intolerance.
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Accepted: May 19, 1971
Received: February 3, 1971
☆This paper was supported by Research Grant AM 14038 and Training Grants AM-04501 and AM-05280 from the National Institutes of Health, United States Public Health Service.
☆☆A preliminary report of this work appeared in abstract form in Clin Res 17: 296, 1968.
© 1971 Published by Elsevier Inc.