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Biomedical subjects

K M Smith

Publications and source records attributed to K M Smith.

At least 181 records · Page 10Linked to original sources
PubMed1984

Temporal response of murine bone marrow to local hyperthermia.

Hemopoietic insufficiency resulting from single or multiple agents used in cancer therapy often becomes a dose limiting toxicity. Since hyperthermia is finding increased clinical application with whole body or extended field treatments for a variety of neoplastic diseases, we wished to examine its potential effects on normal bone marrow. One hind leg of anesthetized mice received up to one hour water bath heating to 41-44 degrees C. With temperatures of 42 degrees C or greater, there was a dose and heating time dependent initial depletion of both CFU-S and CFU-GM that was not appreciably affected by migration of stem cells to or from the heated field. CFU-S and CFU-GM returned to normal values by 2 to 3 weeks after 1 hour heating to 42 degrees C. However, at 43 degrees or 44 degrees C for 1 hour, CFU-GM only transiently returned to normal, falling to 55% and 33% of control respectively by 3 months. Total nucleated cell counts reflected a similar dose and time dependent depletion and repopulation. Finally, bone marrow differential counts from heated marrow suggested that equivalent repopulation along each differentiation pathway occurred during recovery after thermal injury. These data indicate that temperatures greater than 42 degrees C for one hour caused a long term delay in hemopoietic repopulation, which may contribute to a significant toxicity when hyperthermia is used in combination with chemotherapeutic drugs or local irradiation incorporating the same treatment field.

Animals↗
PubMed1984

Polymyalgia rheumatica and rheumatoid arthritis: a prodromal or overlap syndrome?

Seven patients seen over an eight-year period and drawn from a population of approximately one million are described, who presented with unequivocal polymyalgia rheumatica (PMR) and developed sero-positive, erosive rheumatoid arthritis (RA) within a year. Two of the patients were confirmed as having temporal arteritis (TA). The association of PMR and RA is discussed.

Aged↗
PubMed1983

Heme orientational disorder in reconstituted and native sperm whale myoglobin. Proton nuclear magnetic resonance characterizations by heme methyl deuterium labeling in the Met-cyano protein.

The solution proton nuclear magnetic resonance spectrum of the Met-cyano form of sperm whale myoglobin reveals the presence of two sets of comparably intense resonances immediately after reacting the apoprotein with hemin, only one of which corresponds to that of the accepted native protein. Isotope labeling of individual methyl groups of hemin reveals that the methyl assignments differ characteristically in that similar resonance positions for the two components arise from the methyl groups related by a 180 degrees rotation about the alpha-gamma-meso axis. This phenomenon, observed earlier only for myoglobin with modified hemin, dictates that the second protein component in solution immediately after reconstitution must have the heme rotated by 180 degrees about the alpha-gamma-meso axis as compared to that found in the single crystal. The two components in the reconstituted protein equilibrate to yield the spectrum of the native Met-cyanomyoglobin for which there still exists approximately 8% of the minor component. Thus native myoglobin in solution is structurally heterogeneous in the heme pocket. Proton nuclear magnetic resonance spectra of deoxymyoglobin produced from both native and freshly reconstituted protein shown that the heterogeneity is also a property of the physiologically relevant reduced protein forms. It is suggested that, contrary to available X-ray data, heme orientational heterogeneity may be the rule rather than the exception in b-type hemoproteins, and that such disorder must be carefully considered in detailed correlations between structure and function even in native hemoproteins.

Animals↗
PubMed1983

Assignment of hyperfine shifted resonances in high-spin forms of cytochrome c peroxidase by reconstitutions with deuterated hemins.

Assignments of hyperfine shifted proton resonances for the high-spin forms of cytochrome c peroxidase (EC 1.11.1.5) have been made (cytochrome c peroxidase, cytochrome c peroxidase-F) employing the technique of reconstituting the apoprotein with specifically deuterated protohemin IX derivatives. The results show that the heme methyl group pattern differs significantly from similar assignments made for metmyoglobin. In cytochrome c peroxidase the methyl pattern is 5 greater than 1 greater than 8 greater than 3. For cytochrome c peroxidase-F the pattern is 5 greater than 8 greater than 1 greater than 3, but the resonances are not shifted as far downfield and they exhibit a narrower spread. For myoglobin the relative methyl ordering has previously been shown to be 8 greater than 5 greater than 3 greater than 1. Several conclusions have been reached, including confirmation of the essential correspondence between the solution- and crystal-derived data for several heme crevice structural features. The pH dependence of the cytochrome c peroxidase-F methyl resonances is also presented and is shown to differ from native peroxidase. For cytochrome c peroxidase-F smooth, continuous titrations are observed with no evidence of the second conformation which was found for the native enzyme.

Cytochrome-c Peroxidase↗
PubMed1983

Resonance Raman spectra of the heme in leghemoglobin. Evidence for the absence of ruffling and the influence of the vinyl groups.

Resonance Raman spectra of deoxy and carbonmonoxy leghemoglobin (Lb) are compared to the corresponding forms of human adult hemoglobin (HbA). It is found that the heme "core size" indicator line has nearly the same frequency for the two deoxyhemoglobins and the pi-electron density-sensitive line also falls at the same frequency. However, several other modes occur at very different frequencies in the spectra of the two proteins. From an examination of the spectrum of an HbA derivative in which the beta-carbon atoms of the heme vinyl groups were deuterated, it appears that the major differences between deoxy-HbA and -Lb may result from conformational changes in the vinyl groups. No evidence for the suggested ruffling (Irwin, M. J., Armstrong, R. S., and Wright, P. E. (1981) FEBS Lett. 133, 239-243) in deoxy-Lb was found. The spectra of carbonmonoxy-Lb and -HbA were also found to be very different. As in the deoxy case, some of these frequency differences could be attributed to vinyl group conformational differences. However, from the large difference in the pi-electron density-sensitive line, it appears that the vinyl pi-conjugation into the porphyrin in Lb(CO) may be different than it is in HbA(CO). The vinyl conformational differences may be a consequence of the looser heme pocket in Lb than in HbA. The difference in pi-conjugation could make a significant contribution to the difference in ligand binding affinity for these two globins.

Heme↗
PubMed1982

The use of N-methylprotoporphyrin dimethyl ester to inhibit ferrochelatase in Rhodopseudomonas sphaeroides and its effect in promoting biosynthesis of magnesium tetrapyrroles.

N-Methylprotoporphyrin dimethyl ester inhibits ferrochelatase in isolated membranes of Rhodopseudomonas sphaeroides at low concentrations (around 10 nm). Full inhibition developed after a short lag phase. The inhibition was non-competitive with porphyrin substrate. Addition of inhibitor to growing cultures of Rps. sphaeroides caused a decrease (near 40%) in cytochrome content and a severe inhibition of ferrochelatase; the excretion of haem into the medium by cell suspensions was also severely inhibited. The addition of N-methylprotoporphyrin dimethyl ester to suspensions of photosynthetically competent Rps. sphaeroides Ga caused excretion of Mg-protoporphyrin monomethyl ester. When added to mutants V3 and O1, magnesium divinylphaeoporphyrin a5 monomethyl ester and 2-devinyl-2-hydroxyethylphaeophorbide a were excreted, with maximum effect at around 3 microM-inhibitor in the medium. The results are interpreted to suggest that the inhibitor decreases concentration of intracellular haem, which normally controls the activity of 5-aminolaevulinate synthetase. Unregulated activity of this enzyme leads to overproduction of protoporphyrin, which is diverted to the bacteriochlorophyll pathway. Further control operates at magnesium protoporphyrin ester conversion in normal cells.

Cell Membrane↗
PubMed1982

The effect of N-methylprotoporphyrin IX on the synthesis of photosynthetic pigments in Cyanidium caldarium. Further evidence for the role of haem in the biosynthesis of plant billins.

N-Methylprotoporphyrin IX strongly inhibits synthesis of phycocyanobilin, but not chlorophyll a, in the dark. In the light, both phycocyanin and chlorophyll a synthesis are inhibited in parallel. These results are consistent with the intermediacy of haem in algal bilin synthesis and suggest a control mechanism for chlorophyll a synthesis, previously unknown.

Aminolevulinic Acid↗
PubMed1981

Proton nuclear magnetic resonance investigation of the nature of solution conformational equilibria of monomeric insect deoxyhemoglobins.

The proton nuclear magnetic resonance spectra of the three monomeric deoxyhemoglobins of the insect larva Chironomus thummi thummi have been recorded, assigned, and analyzed. In the two allosteric hemoglobins, the heme methyls and vinyl protons were assigned by specific deuterium labeling. The hyperfine-shifted proximal histidyl imidazole exchangeable protons for the three native and two deuteroheme-reconstituted hemoglobins were assigned by comparison of spectra in H2O and 2H2O. Both native and reconstituted allosteric hemoglobins exhibit two sets of interconvertible resonances indicative of two heme orientations differing by a 180 degrees rotation about the alpha-gamma-meso axis, as previously found for the met-cyano analogues [La Mar, G. N., Smith, K. M., Gersonde, K., Sick, H., & Overkamp, M. (1980) J. Biol. Chem. 255, 66]. The relative pH sensitivities of the heme resonance hyperfine shifts for the two allosteric hemoglobins and the apparent pK approximately 8 indicate that the t in equilibrium r allosteric transition, as modulated by the Bohr proton, is being observed. For the native hemoglobins, the t in equilibrium r conformational transition was found to be centered at the heme periphery, with the proximal histidyl imidazole environment insensitive to both pH and the rotational position of the heme, consistent with the absence of a pH influence on the ligation on-rate. For the deuteroheme-reconstituted allosteric hemoglobins, both the heme and axial imidazole environments sense the t in equilibrium r transition, and the histidine environments for the two components for each hemoglobin can be clearly distinguished, suggesting that the ligation on-rates may depend on both pH and heme orientation.

Animals↗
PubMed1980

Mechanism of photooxidation of bacteriochlorophyll c derivatives. A possible model for natural chlorophyll breakdown.

The photooxidation of methyl pheophorbides, derived from bacteriochlorophyll c, yields ring-opened acetylbilitrienes which are structurally related to mammalian bile pigments. The mechanism of this photooxidation, and that of certain mesomethyl-substituted model compounds, has been studied using 18O labeling with molecular oxygen. In all cases, the methine bridge carbon atoms were retained in the ring-opened photoproducts and both oxygen atoms incorporated into the acetylbilitriene photoproducts were derived from a single oxygen molecule. In this respect, ring opening of bacteriochlorophyll c derivatives and mesomethyl-substituted model compounds differs from the nonphotochemical (enzymatic) ring opening of heme which involves elimination of the methine bridge carbon atom as carbon monoxide and insertion of two oxygen atoms, each from a different molecule of molecular oxygen. The process of photooxidation of bacteriochlorophyll c and mesomethyl-substituted model compounds studied may have implications for the mechanism of natural degradation of chlorophyll a and b during leaf senescence and grain ripening.

Bacteria↗
PubMed1980

Proton nuclear magnetic resonance study of the electronic and molecular structure of the heme crevice in horseradish peroxidase.

High field proton nuclear magnetic resonance spectroscopy was used to investigate the electronic and molecular structure of the ferric heme in the resting state of horseradish peroxidase. Deuterium labeling of selected positions of hemin and deuterohemin which were subsequently reconstituted into apo-horseradish peroxidase yielded hyperfine shift patterns for the prosthetic group which are consistent with a ferric porphyrin exhibiting appreciable S = 3/2 character in a quantum mixed spin state. All resolved resonances with significant hyperfine shifts can be accounted for by the porphyrin and a proximal histidyl imidazole, although a sixth ligand from the protein cannot be definitely eliminated. The extremely slow exchange rate with bulk water of the proximal histidyl imidazole exchangeable proton and the absence of deviations from Curie behavior for the porphyrin vinyl and propionic acid proton hyperfine shifts indicate a buried heme crevice which is more rigid than in metmyoglobin. The observation of significant deviations from Curie behavior of the proximal histidyl imidazole exchangeable proton in horseradish peroxidase but not in metmyoglobins is suggested to arise from strong hydrogen bonding between the coordinated imidazole and some unspecified protein acceptor residue in the former protein.

Heme↗