PubMed · 63705
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P R Pannall, D A Maas. 1977-01-08. Danazol and thyroid-function tests.. https://doi.org/10.1016/s0140-6736(77)91125-4
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Retinoidal activity of retinoic acid isomers [all-trans-retinoic acid (ATRA), 9-cis-retinoic acid (9CRA) and 13-cis-retinoic acid (13CRA)] and their oxidized derivatives [19-hydroxy and 19-oxo derivatives of ATRA (19-hydroxy-ATRA and 19-oxo-ATRA), 19-oxo derivative of 9CRA (19-oxo-9CRA), and 19-hydroxy derivative of 13CRA (19-hydroxy-13CRA)] was evaluated by means of a human promyelocytic leukemia HL-60 cell differentiation induction assay. All the compounds examined showed this activity with ED50 values of 2-30 nM, which are in accordance with their binding activity to nuclear retinoic acid receptors (RARs).
Dansylcadaverine, a cationic fluorescent probe binds to bacterial lipopolysaccharide and lipid A, and is displaced competitively by other compounds which possess affinity toward endotoxins. The binding parameters of dansylcadaverine for lipid A were determined by Scatchard analysis to be two apparently equivalent sites with apparent dissociation constants (Kd) ranging between 16 microM to 26 microM, while that obtained for core glycolipid from Salmonella minnesota Re595 yielded a Kd of 22 microM to 28 microM with three binding sites. The Kd of polymyxin B for lipid A was computed from dansylcadaverine displacement by the method of Horovitz and Levitzki (Horovitz, A., and Levitzki, A. (1987) Proc. Natl. Acad. Sci. USA 84, 6654-6658). The applicability of this method for analyzing fluorescence data was validated by comparing the Kds of melittin for lipid A obtained by direct Scatchard analysis, and by the Horovitz-Levitzki method. The displacement of dansylcadaverine from lipid A by polymyxin B was distinctly biphasic with Kds for polymyxin B-lipid A interactions corresponding to 0.4 microM and 1.5 microM, probably resulting as a consequence of lipid A being a mixture of mono- and di-phosphoryl species. This was not observed with core glycolipid, for which the Kd for polymyxin was estimated to range from 1.1 microM to 5.8 microM. The use of dansylcadaverine as a displacement probe offers a novel and convenient method of quantitating the interactions of a wide variety of substances with lipid A.
"Suicide" inactivation of leukotriene (LT) A4 hydrolase/aminopeptidase occurs via an irreversible mechanism-based process which is saturable, of pseudo firstorder, and dependent upon catalysis. Data obtained with either recombinant enzyme or enzyme purified from human leukocytes were similar. Apparent binding constants and inactivation rate constants are equivalent, compatible with a single type of substrate-enzyme complex which partitions between two fates, turnover and inactivation. Both catalytic functions are inactivated, consistent with an overlapping active site for this bifunctional enzyme. The partition ratio (turnover/inactivation) for the LTA4-enzyme complex is 129 +/- 16 for LTA4 hydrolase activity and 124 +/- 10 for aminopeptidase activity. The pH dependence for turnover and inactivation are indistinguishable with a maximum at pH 8. L-Proline p-nitroanilide, a weak substrate with a high Km for the aminopeptidase affords only partial protection against inactivation by LTA4. However, two potent competitive inhibitors, bestatin and captopril, protect both catalytic processes from inactivation, consistent with an active-site specificity for the suicide event. Electrospray ionization mass spectrometry indicates that the molecular weight of pure recombinant enzyme is 69,399 +/- 4 and that covalent modification accompanies catalysis, producing an LTA4:enzyme adduct with a molecular weight 69,717 +/- 4 and a 1:1 stoichiometry. In agreement with kinetic data, electrospray ionization mass spectrometry shows that bestatin inhibits the covalent modification of enzyme by LTA4 and that the extent of modification is proportional to the loss of enzymatic activity.