Guanine nucleotide binding characteristics of transducin: essential role of rhodopsin for rapid exchange of guanine nucleotides

Biochemistry ◽  
1990 ◽  
Vol 29 (15) ◽  
pp. 3804-3812 ◽  
Author(s):  
Ahmad B. Fawzi ◽  
John K. Northup
Keyword(s):  
Essential Role ◽  
Nucleotide Binding ◽  
Guanine Nucleotides ◽  
Guanine Nucleotide ◽  
Binding Characteristics ◽  
Rapid Exchange ◽  
Guanine Nucleotide Binding

Forskolin stimulation of adenylate cyclase in human thyroid membranes

1985 ◽  
Vol 108 (2) ◽  
pp. 200-205 ◽  
Author(s):  
Kikuo Kasai ◽  
Yoshinobu Suzuki ◽  
Masaki Hiraiwa ◽  
Hisamoto Kuroda ◽  
Tatsushi Emoto ◽  
...  
Keyword(s):  
Adenylate Cyclase ◽  
Nucleotide Binding ◽  
Guanine Nucleotides ◽  
Human Thyroid ◽  
Guanine Nucleotide ◽  
Guanine Nucleotide Binding ◽  
Stimulation Of

Abstract. Forskolin stimulates adenylate cyclase in human thyroid membranes approximately 7-fold with halfmaximal stimulation occurring at 5–10 μm. Guanine nucleotides are not required for stimulation of the enzyme by forskolin. Forskolin-stimulation is additive or greater than additive with that of TSH or Gpp(NH)p-(above 1 μm). Different from TSH- or Gpp(NH)p-stimulation of adenylate cyclase, uncoupling of the guanine nucleotide-binding regulatory component by increasing concentrations of MnCl2 did not result in uncoupling of forskolin stimulation. The finding indicates that forskolin may mainly act on the catalytic component of adenylate cyclase. From the present study, it is suggested that the diterpene forskolin stimulates adenylate cyclase in human thyroid membranes by a novel mechanism that differs from TSH- or Gpp(NH)p-stimulation, and that the diterpene may be a useful tool to investigate the metabolism of thyroid and its regulation in normal and pathological situations.

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