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Biomedical subjects

J J Katz

Publications and source records attributed to J J Katz.

At least 19 recordsLinked to original sources
PubMed1998

Cerebral blood flow velocity in patients with subclinical portal-systemic encephalopathy.

UNLABELLED: Alterations in cerebral blood flow (CBF) are implicated in the etiology of portal-systemic encephalopathy. We hypothesized that CO2 reactivity of the cerebral circulation may be impaired in subjects with chronic liver disease (CLD) who also had subclinical portal-systemic encephalopathy (SPSE). We compared the relationship between PETCO2 and cerebral blood flow velocity in 10 patients with CLD with those of 10 healthy control subjects. Middle cerebral artery mean blood flow velocity (MCAMFV) was measured using transcranial Doppler during rest, hyperventilation, and hypoventilation. The degree of SPSE was quantified by using psychometric testing. Patients with CLD had poorer psychometric test scores compared with control subjects. Patients with CLD had lower PETCO2, MCAMFV, and blood pressure values and higher heart rates, differing from control subjects in all ventilation states. However, CO2 reactivity, the rate of change in MCAMFV to changes in ventilation (expressed as percent change in CBF velocity per mm Hg change in PETCO2) was similar for both groups (4.6% +/- 0.6% vs 4.2% +/- 0.5% for patients with CLD versus control subjects, P = 0.15). IMPLICATIONS: Psychometric test scores in patients with chronic liver disease revealed subclinical impairment compared with control subjects. Transcranial Doppler measurements of middle cerebral artery blood flow with varying PETCO2 were conducted, but the CO2 response of patients with liver disease was within the range of control subjects.

Adult↗
PubMed1988

Electron spin resonance of charge carriers in chlorophyll a/water micelles.

Chlorophyll a/water micelles (P740) prepared in hydrocarbon media have been shown by small-angle neutron scattering to consist of hollow cylinders whose surface is formed of a monolayer of chlorophyll crosslinked by water. The micelles can be reversibly oxidized or reduced to generate highly mobile holes or electrons that undergo rapid, one-dimensional transport along the chains of chlorophyll macrocycles comprising the surface of the micelles. Large pi-pi overlap within the chains facilitates the one-dimensional charge transport and is expected to do the same for energy transport. Structural defects in the micelle surface act as boundaries for charge transport, confining the spins to one-dimensional domains of approximately 200 macrocycles. The one-dimensional transport within the limited domains results in motionally narrowed electron spin resonance lines with some residual inhomogeneous broadening. Although the chlorophyll a incorporated in micelles is more easily oxidized than is monomeric chlorophyll a, it is much more resistant to chemical alteration.

Journal Article↗
PubMed1987

Bacteriopheophytin g: Properties and some speculations on a possible primary role for bacteriochlorophylls b and g in the biosynthesis of chlorophylls.

Bacteriopheophytin g and small amounts of bacteriochlorophyll g have been obtained in high purity from the recently discovered photosynthetic bacterium Heliobacterium chlorum. Preparative methods and precautions in handling these sensitive compounds are described. The compounds have been characterized by californium-252 plasma desorption mass spectrometry, HPLC, visible absorption, and electron spin resonance spectroscopy. Our results agree with the structure of bacteriochlorophyll g advanced by H. Brockmann and A. Lipinski [(1983) Arch. Microbiol. 136, 17-19], with the exception that we find the esterifying alcohol to be farnesol and not geranylgeraniol as originally suggested. Zero field splitting parameters of triplet state bacteriopheophytin g and the ESR properties of the cation free radical of bacteriochlorophyll g are reported. The photoisomerization of the subject compounds has been studied. Bacteriopheophytin g undergoes photo-isomerization in white light to pheophytin a with a half-time of approximately 42 min. We suggest that all of the chlorophylls are biosynthesized from a common intermediate containing an ethylidine group, [unk]CH-CH(3), such as is present in bacteriochlorophylls b and g.

Journal Article↗
PubMed1986

Small-angle neutron scattering studies of chlorophyll micelles: Models for bacterial antenna chlorophyll.

Micelles of hydrated chlorophyll a (P740), bacteriochlorophyll a (P865), bacteriochlorophyll c (P750), and pheophytin a prepared in organic media have been studied by small-angle neutron scattering to determine their shape, size, and mass per unit length. All of the micelles are hollow cylinders of well-defined size. The P740 and P750 cylinders are essentially monolayers of macrocycles crosslinked by water, probably in an arrangement similar to that of crystals of chlorophyll derivatives. The P865 micelle is more nearly a bilayer of macrocycles. We show that the curvature necessary to form cylinders probably results from intrinsic curvature of the five-coordinated chlorophyll macrocycle. Studies of P740 micelle formation and the disaggregating effects of another nucleophile (pyridine) are described. As the P750 micelles are nearly identical in size and optical spectra to the rod-shaped structures observed in chlorosomes, and the P865 micelles have optical properties very similar to the in vivo properties of the long-wavelength antenna of purple photosynthetic bacteria, we propose that features of the hydrated cylindrical micelles of these chlorophylls provide good models for antenna chlorophyll in photosynthetic bacteria.

Journal Article↗
PubMed1986

Deuterioglucose: alteration of biodistribution by an isotope effect.

Carbon-14 glucose, in which all carbon-hydrogen bonds were replaced by carbon-deuterium bonds (deuterioglucose), was extracted from algae growing in heavy water and exposed to [14C]carbon dioxide. The identity of [14C]deuterioglucose was confirmed by comparison with authentic material on two high performance liquid chromatography and two thin layer chromatography systems. Fermentation to lactate followed by oxidative decarboxylation demonstrated that 35% of the 14C was on carbons 3 and 4 for deuterioglucose isolated from a 24-hr algal incubation, and 61% for a 20-min incubation. Mice were injected intravenously with either (24-hr) deuterioglucose or with 14C-labeled (protio)glucose labeled uniformly. The deuterioglucose cleared more slowly from the blood, while heart and brain accumulated label more slowly. Tissue concentrations peaked at later times for deuterioglucose. Deuteration may be a useful feature of radiopharmaceutical design.

Animals↗
PubMed1985

Biological effects of background radiation: mutagenicity of 40K.

The naturally occurring radioactive isotope 40K is the single largest contributor to the internal background radiation dose in living organisms. We examined cell growth and mutation rate or frequency in several strains of Escherichia coli in (i) media containing the natural content of 40K, (ii) media containing potassium from which essentially all of the 40K had been removed by isotope separation, and (iii) media highly enriched in 40K. Growth rates (doubling times) were identical in the present or absence of 40K. In more than 40 chemostat experiments, we were unable to detect any significant differences in mutation rate to bacteriophage T5 resistance or in mutation frequency to valine resistance or tryptophan prototrophy attributable to 40K. We conclude that, in the bacterial systems we have studied, 40K does not make a significant contribution to spontaneous mutation.

Dose-Response Relationship, Radiation↗
PubMed1984

Cross-polarization/magic-angle sample-spinning C NMR spectroscopic study of chlorophyll a in the solid state.

Solid-state cross-polarization/magic-angle sample-spinning (13)C NMR spectra have been recorded on chlorophyll a-water aggregates, methyl pyrochlorophyllide a, and methyl pyropheophorbide a (derivatives that lack a phytyl chain). Spectra have also been collected under a decoupling regime in which resonances of certain hydrogen-bearing carbon atoms are suppressed. These observations are used to assign the solid-state spectra.

Journal Article↗
PubMed1980

Photophysical properties of zinc and magnesium tris(pyrochlorophyllide a) 1,1,1-tris(hydroxymethyl)ethane triesters.

The zinc and magnesium tris(pyrochlorophyllide a) 1,1,1-tris(hydroxymethyl)ethane triesters have properties that are very similar to those exhibited by pairs of pyrochlorophyll a or chlorophyll a linked by ethylene glycol through their propionic acid side chains. In the open configuration, the fluorescence lifetimes and emission spectra of the triesters resemble those of chlorophyll a monomers. However, the triesters have a mechanism for energy dissipation not present in monomeric chlorophyll a, which prevents the build-up of significant concentrations of molecules in S(1) states. Optical pumping of these compounds in their folded configuration results in the formation of high concentrations of molecules in S(1) states and in laser light emission, which originates from the two folded macrocycles. The optical data indicate that efficient energy transfer occurs from the open to the folded configurations.

Journal Article↗
PubMed1980

Self-assembled chlorophyll a systems as studied by californium-252 plasma desorption mass spectroscopy.

Self-assembled chlorophyll a and pheophytin a systems in thin solid films have been studied by (252)Cf plasma desorption mass spectrometry (PDMS). The (252)Cf-PDMS spectra of these films show monomer cation and anion molecular ions, ions of molecular aggregates, and positive and negative ion fragmentation patterns arising from the loss of various aliphatic side chains from the chlorin ring. Chlorophyll a films cast from dry carbon tetrachloride solution, in which chlorophyll a is known to occur as the dimer, produced an abundant dimer ion. The highest degree of chlorophyll a self-assembly was observed in chlorophyll a films cast from n-octane solutions. Oligomer ions extending upwards in size to the heptamer were detected in this system.

Journal Article↗
PubMed1978

Coherent stimulated light emission (lasing) in covalently linked chlorophyll dimers.

The covalently linked chlorophyll a dimer exhibits remarkably different properties in the folded and open configurations. In the folded configuration the absorption maximum is at 695 nm and the fluorescence maximum is at 730 nm. Laser output at 733 and 735 nm is obtained for solutions in wet benzene and 0.1 M ethanol/toluene, respectively. Measurements of fluorescence lineshapes, made with a transverse excited atmospheric (TEA) nitrogen laser for excitation, show the lifetime shortening associated with stimulated emission resulting from appreciable concentrations of molecules in S(1) excited states. In contrast, the open dimer has absorption and fluorescence spectra essentially the same as those of chlorophyll a monomer. Unlike either the folded dimer or chlorophyll a monomer, the open dimer shows no laser emission or fluorescene lifetime shortening. It does not appear that the behavior of the open dimer can be explained in terms of excimer or triplet formation or by nonradiative decay processes. It is suggested that absorption of the exciting radiation by S(1), leading to the formation of an exciplex or charge transfer state, may be involved. Significantly, no large changes in fluorescence quantum yield or fluorescence lifetime are observed for these dimers as compared to monomer chlorophyll. This suggests that concentration quenching and lifetime shortening in condensed chlorophyll systems involve more than the simple proximity of two chlorophyll molecules.

Journal Article↗
PubMed1977

Chlorophyll lasers: Stimulated light emission by chlorophylls and Mg-free chlorophyll derivatives.

Stimulated emission and lasing have been demonstrated for chlorophyll a, chlorophyll b, and bacteriochlorophyll a as well as for the Mg-free chlorophyll derivatives pheophytin a and methyl pheophorbide a. Population inversion was obtained by optically pumping with an N(2) laser. For the three chlorophylls, lasing was observed for only the (0,0) vibronic region of the S(1) --> S(0) fluorescence band. In contrast, lasing was observed for both the (0,0) and (0,1) vibronic regions of the S(1) --> S(0) fluorescence band of pheophytin a and methyl pheophorbide a. Differences between the lasing behavior of the chlorophylls and the Mg-free derivatives probably reflect differences in aggregation behavior. Laser pulses of duration shorter than the fluorescence lifetimes were generated. This result suggests that stimulated emission must be considered in the interpretation of fluorescence lifetime data for in vitro and in vivo chlorophyll-containing systems.

Journal Article↗
PubMed1976

Biosynthesis of deuterated riboflavin: structure determination by NMR and mass spectrometry.

The riboflavin-producing fungus Eremothecium ashbyii was cultured in various growth media containing high concentrations of deuteriuj, and the product was isolated. The structures of highly deuterated riboflavin, in which at least 13 of 15 nonexchangeable hydrogens were replaced by deuterium, and fully deuterated riboflavin, in which all 15 nonexchangeable sites contained deuterium, were established by NMR and mass spectrometry. The aromatic protons (C-5 and C-8) wer partially substituted in the highly deuterated molecule. Information regarding three areas of the biosynthetic pathway within the microorganism was obtained as a result of the formation of these compounds. Extensive solvent interaction, possibly due to passage of sugar through the transaldolase-transketolase pathway, occurs during formation of the ribityl chain. Limited solvent participation takes place during formation of 6,7-dimethyl-8-ribityllumazine, the immediate precursor of riboflavin. Deuteration of the riboflavin C-6 and C-7 methyl groups indicates significant solvent exchange during the final step of the biosynthetic process.

Deuterium↗