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Biomedical subjects

A Moscowitz

Publications and source records attributed to A Moscowitz.

At least 19 recordsLinked to original sources
PubMed1986

The binding of the antitumor antibiotic chartreusin to poly(dA-dT).poly(dA-dT), poly(dG-dC).poly(dG-dC), calf thymus DNA, transfer RNA, and ribosomal RNA.

Chartreusin binds cooperatively to poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC). Both the site-exclusion model and the specific site model yield cooperative binding constants of about 5 X 10(5) M-1 and 3 X 10(5) M-1 for the AT and GC polymers, respectively, and the same stoichiometry and intrinsic binding constant for both polymers of 5 nucleotides per binding site and 3.1 X 10(4) M-1. The Scatchard plot for calf thymus DNA is curved in the opposite sense from that of cooperative binding. These binding data did not fit the site-exclusion model with the cooperative binding parameter as a variable nor the specific site, negative-cooperative binding model. The site-exclusion model with a cooperative binding parameter of unity yielded a binding constant of about 4 X 10(4) M-1 and a stoichiometry of about 5 nucleotides per binding site. The same model for transfer and ribosomal RNA yielded binding constants of 5 X 10(3) M-1 and 7 X 10(3) M-1 and stoichiometries of about 13 and 6 nucleotides per binding site, respectively.

Antibiotics, Antineoplastic↗
PubMed1980

Magnetic circular dichroism analysis of the IHP effect on spin equilibria in human ferric hemoglobins.

Magnetic circular dichroism (MCD) spectroscopy has been to explore the connection between optical spectra and the high spin population of several hemoglobins under various conditions. It is found that the effectiveness of IHP in inducing spectral changes can be markedly affected by solvent. For example, the IHP-induced spectral changes in the visible region for nitritomethemoglobin-A in mixed buffer solvent systems (glycerol or polyethylene glycol (PEG), mw 190-210) are more than double those observed in aqueous buffers. We estimate that IHP induces a mix of R/T forms in bis-tris phosphate buffers, for NO-2metHb that is only about 50%. While PEG and glycerol both lead to enhanced IHP-induced spectral differences, they behave differently in two aspects. PEG shifts the visible MCD and absorption spectra of F-metHb-A, supposedly already biased towards the T form by ligand, in the same direction that IHP does. PEG also maximizes the spin state changes with IHP for three R from hemoglobins and N-3metHb-A, and so appears to stabilize the T form in all cases. Glycerol does not. In addition, the apparent binding constant for NO-2 to H2OmetHb-A differs between these two solvents. Comparison of the data from several hemoglobins leads to the conclusion that the changes in spin state distributions induced by IHP correlate well with quaternary structure for a given hemoglobin. An analogous correlation amongst various proteins between initial spin state distribution (IHP) absent) and quaternary structure is not found.

Circular Dichroism↗
PubMed1974

On the existence of a mono-vinyl d-urobilin.

Chromic acid degradation of a d-urobilin, obtained after incubation of bilirubin in fecal bacterial cultures, gave methylvinylmaleimide and methylethylmaleimide. The d-urobilin, molecular weight 588, C(33)H(40)-N(4)O(6), clearly showed the presence of both vinyl and ethyl resonances in the nuclear magnetic resonance spectrum. These results point unambiguously to a urobilin structure with one vinyl and one ethyl beta-substituent.

Acids↗
PubMed1971

The absolute configuration of natural (-)-stercobilin and other urobilinoid compounds.

Chromic acid degradation of natural (-)-stercobilin (1) yields 2(R)-methyl-3(R)-ethylsuccinimide (+2), whereby the absolute configuration of 1 at the chiral centers C-1, C-2, C-7, and C-8 is established. The substituted oxo-tetrahydrodipyrromethane precursor, 5, for the total synthesis of (-)-stercobilins 3 and 4, in which the relative configuration between the asymmetric centers is known, yields 2(S)-methyl-3(S)-ethylsuccinimide (-2) under the same conditions of degradation. Nuclear magnetic resonance studies of 1 and 3 show that in 1 the hydrogen atoms at C-2 and C-2', as well as those at C-7 and C-7', are trans relative to one another. Accordingly, natural (-)-stercobilin possesses the 2'(S), 7'(S) configuration, and has the configuration formula 6(1 (R), 2(R), 2'(S), 7'(S), 7(R), 8(R)). These results, coupled with those of earlier studies, also establish the absolute configuration of the (+)-urobilin 7 and of the phycobilin 8 at C-7'.

Chromates↗
PubMed1970

Circular dichroism studies at variable temperature: urobilinoid conformation.

Measurements of the temperature dependence of the circular dichroism spectra of l-stercobilin and d-urobilin show that the conformations of these optically-active urobilinoids change with temperature between 163 and 297 degrees K. These conformational changes depend critically on the hydrogen bonding characteristics of the solvent. Thus, in methanol-glycerol (9:1), the chiral sense of the helical conformation of the dipyrrylmethene chromophore is reversed on lowering the temperature, whereas in chloroform, reversal does not occur.

Bile Pigments↗