Multiple expressions of the activity of guanine nucleotide regulatory protein in human thyroid adenylate cyclase |
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Authors: | Sania Amr Pierre Carayon Michael C Lin |
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Institution: | 1. Developmental Endocrinology Branch, NICHD, NIH, and Laboratory of Cellular and Developmental Biology, NIADDK NIH, Bethesda, Maryland 20205 U.S.A.;2. Laboratoire de Biochimie Medicale-U 38 INSERM, Marseille, France |
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Abstract: | Adenylate cyclase (ATP pyrophosphate-lyase, EC 4.6.1.1) in plasma membranes from human thyroid was highly responsive to thyrotropin. Pretreatment of thyroid plasma membranes with 5′-guanylylimidodiphosphate (Gpp(NH)p) in the presence of Mg2+ led to a temperature-dependent activation, which was seen neither in the absence of Mg2+ nor at 4 °C. By contrast, thyrotropin bound to its receptors regardless of the temperature and produced its maximal effect after 2 min of preincubation in the absence or presence of Mg2+. Furthermore, activation was seen after treatment with thyrotropin and Gpp(NH)p even carried out in the absence of Mg2+ or at 4 °C. However, the full activation by Gpp(NH)p required Mg2+, hormone, and elevated temperature. These observations suggest that there appears to be two types of nucleotide interaction responsible for the Gpp(NH)p activation in human thyroid membrane; one type seen in the absence of hormone may represent the system uncoupled from hormone receptor, while the fully coupled hormone-sensitive adenylate cyclase accounts for the second type of interaction which requires the presence of hormone. |
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Keywords: | To whom all correspondence should be addressed: National Institutes of Health Bldg 10 Rm 10B09 Bethesda Md 20205 |
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