Reappraisal of the inhibitory effect of certain sugars used as osmotica on phenylalanine ammonia-lyase activity |
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| Authors: | Jonathan E Poulton Duncan McRee Eric E Conn James A Saunders Denise E Blume Jerry W McClure |
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| Institution: | 1. Department of Biochemistry and Biophysics, University of California, Davis, CA 95616 U.S.A.;2. Tobacco Laboratory, USDA, SEA, Beltsville, MD 20705 U.S.A.;3. Department of Botany, Miami University, Oxford, OH 45056, U.S.A. |
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| Abstract: | An earlier report that various sugars, especially d-mannitol and d-sorbitol, severely inhibited phenylalanine ammonia-lyase (PAL)1 activity from tobacco in vitro has been reappraised. This apparent inhibition resulted from complexing of the sugars with borate, used as buffer system in that study, leading to an undetected pH decrease. We find that d-mannitol, d-sorbitol, d-glucose and sucrose are not inhibitory to PAL preparations obtained from sweet-clover leaves or from protoplasts of tobacco and barley, when alternative buffers are used for the assay. Moreover, the inhibition of barley PAL due to borate—sugar complex formation was completely eliminated by readjusting the pH of the reaction mixture to 8.8 before assaying. |
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| Keywords: | Leguminosae sweet clover Gramineae barley Solanaceae tobacco phenylalanine ammonia-lyase borate—carbohydrate complexes assay pH changes |
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