Photochemical reactions of LAC repressor. Effects on inducer binding. |
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Authors: | M Charlier F Culard J C Maurizot C Helene |
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Affiliation: | Endocrinology and Metabolism, Department of Medicine, University of Florida School of Medicine, Gainesville, Florida 32610 USA |
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Abstract: | Insulin was tritiated by exposure to tritium gas activated by microwave radiation. 3H-insulin competed with 125I-insulin for binding to cultured human lymphocytes and to anti-insulin antibody to the same extent as did native insulin. The affinity constant for the binding of 3H-insulin to specific receptors on cultured human lymphocytes was 0.48 × 109 M?1 (SD-0.06). The affinity constant for the binding of 125I-insulin was 0.57 × 109 M?1 (SD=0.23). As was the case with 125I-insulin, the Scatchard plot of the binding of 3H-insulin to human lymphocytes was curvilinear, suggesting the presence of a heterogeneous population of receptors, or of a homogeneous population of receptors that exhibit negative cooperativity. The similarity observed between 3H-insulin and 125I-insulin helps refute the argument that distortion of the insulin molecule caused by introduction of an iodine atom may interfere with its binding to insulin receptors. |
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