Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 51:289-294 (1973)
© 1973 American Society of Plant Biologists

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Articles

Multiphasic Absorption of Glucose and 3-O-Methyl Glucose by Aged Potato Slices 1

Juri Linask2 and George G. Laties

a Department of Biology and Molecular Biology Institute, University of California, Los Angeles, California 90024

The isotherm for glucose absorption by aged potato (Solanum tuberosum var. Russet Burbank) discs shows four distinct phases in the concentration ranges 1.0 to 75 µM, 75 µM to 1.5 mM, 1.5 to 15 mM, and 15 to 100 mM, respectively. Each segment of the multiphasic isotherm, when plotted reciprocally by the method of Lineweaver and Burk or of Hofstee, without regard for uptake in earlier phases, indicates absorption rate to be a hyperbolic function of concentration. The observations suggest that glucose uptake is carrier-mediated, and that the transport barrier undergoes a series of all-or-none transformations at critical external concentrations, yielding successive new and higher values for the parameters Km and Vmax 3-O-Methyl glucose, a nonmetabolizable analogue of glucose, shows the same multiphasic absorption isotherm, with Km values essentially similar to those for glucose uptake, and Vmax values somewhat lower than those for glucose absorption. Whereas the first three phases of the absorption isotherm are taken to reflect passage across the plasma membrane, the fourth phase may reflect kinetics of glucose or 3-O-methyl glucose transport to the vacuole.

2 Present address: Department for Sick and Injured, Pennsylvania Hospital, Philadelphia, Pa. 19107.

1 The work herein generously was supported by a grant from the United States Atomic Energy Commission.






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