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Results for “Optical Rotatory Dispersion”

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At least 865 records · Page 48Linked to original sources
PubMed1980

Evidence that (+)-bupranolol interacts directly with myocardial beta-adrenoceptors. Control of optical purity with differential thermal analysis.

Melting points measured with the capillary method were 150.5 degree C, 150.5 degree C and 224.0 degree C for hydrochlorides of (+)-bupranolol, (-)-bupranolol and (+/-)-bupranolol, respectively. The large difference in melting points of 73.5 degree C prompted us to determine possible contaminations of (+)-bupranolol with traces of (-)-bupranolol using differential scanning calorimetry. We detected as little as 0.001% (-)-bupranolol in a standard mixture of (+)-bupranolol and (-)-bupranolol. A batch of (+)-bupranolol not measurably contaminated with (-)-bupranolol (optically purity greater than 99.999%) was used in pharmacological and biochemical assays. The affinities of (-)-bupranolol and (+)-bupranolol were determined functionally by the blockade of isoprenaline stimulation of spontaneously beating rat right atria and electrically driven kitten papillary muscles; and directly by inhibition of binding of 3H-(-)-propranolol to kitten ventricle membrane particles. In all 3 systems the enantiomeric (-)/(+) affinity ratio was 50--120 for bupranolol. These experiments prove that (+)-bupranolol itself binds to the beta-adrenoceptors of mammalian myocardium.

Animals↗
PubMed1977

Spectral studies on the conformation of rhodopsin.

A summary is given of visible and ultraviolet spectral studies which deal with the conformation of rhodopsin in situ and solubilized with detergent. Emphasis is placed on studies which give specific information about the macromolecular structure and which set quantitative limits on the magnitude of light-induced conformational changes.

Animals↗
PubMed1979

Conformational effects of coenzyme binding to porcine lactic dehydrogenase.

Changes induced on addition of the coenzyme, NADH or NAD+, to porcine lactic dehydrogenase isoenzymes H4 and M4 have been studied by hydrodynamic and spectroscopic methods. As shown by ultracentrifugal analysis, the native subunit structure remains unchanged on holoenzyme formation; an approximately 5% increase of the sedimentation coefficient, parallelled by a slight decrease of the partial specific volume (less than 1%) indicate a significant change in the native tertiary and/or quaternary structure of the enzymes, corroborating earlier calorimetric data (Hinz and Jaenicke, 1975). The binding constant for the enzyme from skeletal muscle (M4) and NADH are found to be in agreement with KD-values obtained from equilibrium dialysis, as well as spectroscopic and thermal titration experiments (8 muM). Far UV circular dichroism measurements do not show significant changes on ligand binding, indicating unchanged helicity or compensatory conformational effects. In the near UV, ligand binding is reflected by an extrinsic Cotton effect around 340 nm; in the range of aromatic absorption no changes are detectable. The experimental results suggest that there are gross structural changes on coenzyme binding to lactic dehydrogenase which do not affect the intrinsic spectral properties normally applied to analyze transconformation reactions in protein molecules.

Animals↗
PubMed1996

Enantioselective autocatalysis. IV. Implications for parity violation effects.

Historically, parity violation at the contemporary biomolecular level (i.e., only L-amino acids in proteins and D-sugars in DNA and RNA) has been postulated to be the inevitable result of parity violations at the elementary particle level, involving either beta-decay electrons or parity violating energy differences (PVEDs) between enantiomers. These two chiral biases have in turn allegedly impressed a small but persistent chirality onto prebiotic chemistry which, after appropriate amplification, has culminated in our contemporary homochiral biopolymers. Experiments and controversies pertaining to the efficacy of these two chiral biases are reviewed briefly, with the conclusions that: a) there is no experimental evidence supporting the capability of beta-decay electrons or other spin-polarized chiral particles to generate chiral molecules, and b) only theoretical calculations, but no experimental evidence, support the allegation of a causal relation between PVEDs and biomolecular homochirality. We here attempt to examine the latter allegation experimentally. Spontaneous resolution under racemization conditions (SRURC) during the crystallization of the bromofluoro-1,4-benzodiazepinooxazole derivative I is capable of affording products of high enantiomeric purity. This process, which involves very efficient stereoselective autocatalysis, has now been examined statistically. If PVED effects are operative, the SRURC of racemic I should provide, either exclusively or with a strong and consistent bias, only one enantiomer of crystalline I. However, crystallization experiments of racemic I showed no bias in its SRURC, leading to the conclusion that PVED effects are ineffective in dictating a preferred chirality in this system. Several earlier experiments in the literature leading to a similar conclusion as to the inefficacy of PVED effects in promoting a preferred chirality are noted.

Amino Acids↗