Influence of temperature and denaturing agents on the structural stability of calmodulin. A 1H-nuclear magnetic resonance study

The structural stability of calmodulin was studied by 1H-nuclear magnetic resonance spectroscopy under different denaturing conditions. The presence of Ca2+ stabilizes the structural properties of the native protein. In the absence of calcium the structural integrity of calmodulin can easily be affected by elevated temperatures or by high concentrations of denaturing agents. The unfolding process under various denaturing conditions is reversible underlining the high degree of structural flexibility of this protein.

Influence of Ca2+ and trifluoperazine on the structure of calmodulin. A 1H-nuclear magnetic resonance study

Ca2+-induced conformational changes of calmodulin under a variety of different experimental conditions have been studied by 1H-nuclear magnetic resonance techniques. The assignment for Tyr-99 has been corrected. Ca2+ titration performed at pH 7.5 and greater than 9.5 apparently induces a different sequence of the protein folding process as can be monitored by the resonances of His-107. These two structural forms cannot be interconverted. The phenylalanine residue(s) responsible for the resonances at 6.47 ppm (Ca2+-free form) and 6.64 ppm (Ca2+-saturated form) respectively, are apparently located close to Ca2+-binding sites III and IV. This can be recognized from nuclear Overhauser enhancement and Gd3+-broadening techniques. Gd3+-broadening experiments classify Ca2+-binding site IV as the site with the highest Gd3+/ca2+-exchange rate. The antipsychotic drug trifluoperazine, which is known to bind to calmodulin in a calcium-dependent way [Levin, R. M. and Weiss, B. (1977) Mol. Pharmacol. 13, 690-697], has been found to induce a conformational change of the Ca2+-saturated form of calmodulin. The methionine and phenylalanine residues were especially affected. Possible binding site(s) for trifluoperazine are discussed.

Hormones and the pathophysiology of fibrocystic mastopathy: elevated luteinizing hormone levels

Serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, testosterone, estrone, and estradiol were measured weekly for 1 month in 12 menstruating women with fibrocystic mastopathy. LH levels were abnormally elevated. The remainder of hormone levels were essentially normal. Elevated serum LH may be secondary to hypothalamic-pituitary, ovulatory, or corpus luteum dysfunction. The roles of hormonal abnormalities in the pathogenesis of fibroycstic mastopathy are not known.