Anaerobic stimulation of sugar transport in avian erythrocytes |
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Authors: | Joseph Y Cheung David M Regen Madge E Schworer Carol F Whitfield Howard E Morgan |
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Institution: | 1. Department of Physiology, The Milton S. Hershey Medical Center, The Pennsylvania State University, Hershey, Pa. 17033, U.S.A.;2. Department of Physiology, School of Medicine, Vanderbilt University, Nashville, Tenn. 37232, U.S.A. |
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Abstract: | The kinetic parameters of the sugar transport in avian erythrocytes were evaluated under aerobic and anaerobic conditions. In anaerobic cells, transport measurements with methylglucose resulted in a set of similar dissociation-like constants. Thus the Michaelis constants of methylglucose entry and exit, and , were 8 and 7 mM, respectively. The equilibrium exchange constant, , and the counterflow constant, , were 9 and 11 mM, respectively. The activity constant for transport, , defined as , was 4 ml/h per g. This set of kinetic constants was compatible with a symmetrical mobile-carrier model. In contrast, the Michaelis constant for glucose entry, , was 2 mM and less than the counterflow constant, (8 mM). This result could be accounted for by slower movement of the glucose-carrier complex than the free carrier. The activity constant for glucose transport, , was 5 ml/h perg.Under aerobic conditions, two of the dissociation-like constants ( and ) for transport were significantly larger than those obtained in anaerobic cells, but the remaining two ( and ) remained unchanged. The values, for were 8, 26, 20 and 8 mM, respectively. The activity constant, , decreased to 2 ml/h per g. These changes in kinetic constants were consistent with the hypothesis that anoxia accelerated sugar transport by releasing free carrier that was previously sequestered on the inside of the cell membrane. |
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