Search PubMed⌕ Search

Biomedical subjects

R C Davis

Publications and source records attributed to R C Davis.

At least 91 records · Page 5Linked to original sources
PubMed1982

Giant circular dichroism of high molecular weight chlorophyllide-apomyoglobin complexes.

Chlorophyllide a and the apoprotein of myoglobin (Mb) spontaneously form three types of complex. The M (M(r) approximately 3 x 10(5)) and H (M(r) >/= 4 x 10(6)) complexes, but not the L (M(r) approximately 1.7 x 10(4)), display a circular dichroism (CD) spectrum that is highly red-shifted, nonconservative, and very intense-characteristics shared by the CD spectra of reaction center complexes from purple photosynthetic bacteria. At its 710-nm peak, the H complex CD spectrum has a larger magnitude, 0.06 differential absorbance per unit total absorbance, than has been reported for chlorophyll in any medium.

Journal Article↗
PubMed1982

Interaction of D-phenylalanine with Co(II)-substituted rabbit muscle pyruvate kinase: kinetic and optical properties.

The kinetic and optical properties of Co(II)-substituted pyruvate kinase in the presence of D-phenylalanine (D-Phe) were investigated. The results are discussed in comparison with the effects of its optical isomer L-phenylalanine (L-Phe) on the same enzyme. The catalytic effect of D-Phe on rabbit muscle pyruvate kinase depended upon the nature of the activating divalent metal ion used. It has stimulatory effect on Mg(II)-activated enzyme, but inhibitory effect on Co(II)-activated enzyme. Unlike the inhibitory effect of L-Phe, the inhibition of Co(II)-enzyme by D-Phe was not sensitive to the changes of pH and temperature, could not be reversed by L-alanine (L-Ala), displayed hyperbolic kinetics, and was noncompetitive with respect to phosphoenopyruvate saturation. D-Phe induced substantial visible circular dichroism (CD) spectral changes of Co(II)-enzyme similar to those induced by L-Phe. Although ultraviolet CD spectrum was not affected, D-Phe induced an ultraviolet difference absorption spectral change very similar to, but much smaller than, that induced by L-Phe. Our results support that D-Phe and other amino acids interact with the enzyme at two different sites: a common site, causing similar conformational changes which bear little direct kinetic relevance, and a kinetically relevant site, which is sterically dependent upon the side chain of the amino acids.

Animals↗
PubMed1981

Salmonella sepsis in infancy.

Of seven infants with Salmonella sepsis, three had meningitis. A review of these cases and others previously reported demonstrated that among infants less than 1 year old in Arkansas, Salmonella infection developed in 383 over a 31/2-year period. The reported incidence of sepsis and/or meningitis was 1.8%; for those less than 2 months of age, it was 5.0%. Epidemiologic investigation failed to disclose a consistent source of the Salmonella colonization for young infants. Treatment of meningitis with ampicillin sodium was frequently associated with relapse or clinical failure, while chloramphenicol or a chloramphenicol-ampicillin combination appeared to offer superior efficacy. Consideration should be given to antibiotics for the routine treatment of Salmonella gastroenteritis in infants less than 3 months of age.

Ampicillin↗
PubMed1981

L-phenylalanine induced changes of sulfhydryl reactivity in rabbit muscle pyruvate kinase.

Reactivity of sulfhydryl groups in rabbit muscle pyruvate kinase toward 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) was studied in the presence of activating divalent metal ions, substrate, substrate analogue, and the allosteric inhibitor, L-Phe. The pattern of sulfhydryl modification in various complexes of pyruvate kinase was consistent with the extent of enzyme inactivation by DTNB under very similar conditions. The sulfhydryl reactivity of Mg(II)-, Co(II)-, and Mn(II)-substituted pyruvate kinase toward DTNB depended upon the nature of the activating divalent metal ions used in the following order of increasing potency, Mg(II) less than Mn(II) less than Co(II), which is inversely related to the order of catalytic efficiency of these metal ions at alkaline pH. Similar optical spectra and the patterns of sulfhydryl modification by DTNB of the metal derivatives of pyruvate kinase were observed upon the binding of the substrate, phosphoenolpyruvate (PEP), or the substrate analogue, phosphoglycolate, which also provided a complete protection against enzyme inactivation by DTNB. L-PHe, on eht other hand, deprotected the enzyme from inactivation and further sulfhydryl modification by DTNB in the presence of PEP with the following order of potency depending upon the activating metal ions, Mn(II) less than Co(II) less than Mg(II), which parallels the order of metal dependency of L-Phe inhibition of this enzyme. L-Ala, which reverses the L-Phe inhibition of Mg(II)- or Co(II)-activated enzyme, restored the protective effect of PEP in the presence of L-Phe. The different patterns of sulfhydryl reactivity toward Mn(II)-enzyme (hyperbolic) and Mg(II)-enzyme (sigmoidal) correspond well with their kinetic patterns in the presence of L-Phe, indicating the presence of different conformational states between these two metal-enzyme complexes. These results led us to conclude that enzyme sulfhydryl reactivity toward DTNB can be used as a valid index for allosteric conformational changes of rabbit muscles pyruvate kinase.

Alanine↗
PubMed1980

Chronic intravascular hemolysis after aortic valve replacement with Ionescu-Shiley xenograft: comparative study with Bjork-Shiley prosthesis.

Twenty patients with a prosthetic valve (Ionescu-Shiley or Bjork-Shiley) in the aortic position were studied for evidence of intravascular hemolysis. Serum lactic dehydrogenase and serum haptoglobin levels were used as the most sensitive indicators of hemolysis. Elevated concentrations of lactic dehydrogenase were found in all 10 patients with an Ionescu-Shiley prosthesis (mean 402 IU/liter) and in 7 of 10 patients with a Bjork-Shiley prosthesis (mean 234 IU/liter). The mean serum haptoglobin was 15 mg/dl (range 10 to 28) in patients with the Ionescu-Shiley valve and 96 mg/dl (15 to 284) for those with the Bjork-Shiley valve. This study indicates the presence of chronic intravascular hemolysis in patients with the Ionescu-Shiley aortic valve. The increase in lactic dehydrogenase was significantly greater in patients with the Ionescu-Shiley prosthesis than in those with the Bjork-Shiley prosthesis, indicating a slightly shorter red cell life span in the former group.

Adult↗
PubMed1980

pH-dependent amino acid induced conformational changes of rabbit muscle pyruvate kinase.

The interactions of L-Phe and L-Ala with rabbit muscle pyruvate kinase dependend upon the nature of divalent metal ions sutdied: Mg(II), Co(II), Mn(II), and Ni(II). L-phe inhibited all metal derivatives of the enzyme except Mn(II)--enzyme. L-Ala inhibited only Ni(II)--enzyme and had no effect on other metal derivatives. The inhibition by L-Phe could be partially or completely reversed by L-Ala for all metal derivatives. The mode of inhibition of pyruvate kinase by L-Phe depended upon pH as well as the nature of activating divalent metal ions. The sigmoidal response increased with increasing pH for all metal derivatives inhibited by L-Phe. L-Phe and L-Ala strongly perturbed the coordination sphere of enzyme bound Co(II), but not Ni(II). There were poor correlations between visible circular dichroic (cd) spectral changes and the corresponding kinetic changes. However, L-Phe and (or) L-Ala induced ultraviolet cd and difference absorption spectral changes, on the other hand, corresponded remarkably well with the kinetic observations.

Alanine↗
PubMed1980

Comparative studies of kinetic and optical properties of rabbit muscle, sturgeon muscle, and yeast pyruvate kinase.

The kinetic and optical properties of pyruvate kinase isolated from rabbit muscle, sturgeon muscle, and yeast were compared using various activating divalent metal ions as probes for functional features and using ultraviolet circular dichroism (cd) measurements for conformational features, respectively. All three preparations of pyruvate kinase were similar in many aspects, such as activating efficiencies of the four activating metal ions, Mg(II), Co(II), Mn(II), and Ni(II) and pH-rate profiles, suggesting the presence of a similar metal binding locus of these enzymes as well as a common underlying mechanism of action. L-Phe inhibited the rabbit muscle enzyme and turned the hyperbolic kinetics into a sigmoidal kinetic with respect to phosphoenolpyruvate at alkaline pH, while fructose-1,6-biphosphate activated the sturgeon muscle and yeast enzymes and turned the sigmoidal kinetics into hyperbolic kinetics with respect to phosphoenolpyruvate. The ultraviolet cd spectral changes qualitatively correlated well with kinetic observations of all three native enzymes in the presence and absence of allosteric effectors. Our results suggested that there are at least two conformational states of pyruvate kinase which are inducible by the binding of substrate and (or) allosteric effectors. The conformational changes from one form to another in these enzymes are very similar, especially between the rabbit and sturgeon muscle enzymes.

Animals↗
PubMed1978

De novo development of membranous nephropathy in cadaver renal allografts.

Glomerulonephritis in transplant recipients often reflects recurrence of the immunopathogenetic mechanism causing the original renal disease. Membranous nephropathy (MN), a progressive immune complex mediated glomerular disease and the commonest cause of idiopathic nephrotic syndrome in adults, has been virtually unreported in transplant recipients. Two cases are reported here of typical MN (by clinical, light, immunofluorescent and electron microscopic criteria) developing de novo in the transplants of patients whose original diseases were anti-GBM nephritis and focal glomerular sclerosis. NM developed following episodes of viral hepatitis and renal infarction respectively. Possible mechanisms by which this lesion might develop in these patients are investigated and discussed. Chronic immune complex nephropathy (MN) can develop de novo in immunosuppressed transplant recipients apparently initiated by events in the post-transplant period.

Adolescent↗
PubMed1977

Circular dichroism of cobaltous complexes of creatine kinase.

Circular dichroic spectra in the visible wavelength region were used to investigate the local environment of Co(II), an activating metal, at the active site of rabbit muscle creatine kinase. There was a small spectral change when CoADP- was bound to creatine kinase, no change when creatine was added, and another small change when NO3- was added to form the transition state analogue. Using matrix rank analysis to quantitate these small spectral changes, a titratable group with a pK = 7.4 was found which modified the enzyme-bound metal-nucleotide interaction. These data suggest that, throughout the enzyme's catalysis, the metal-nucleotide interaction remains very similar in structure to the complex not bound to the enzyme.

Adenosine Diphosphate↗
PubMed1977

A comparison of the late patency rates of axillobilateral femoral and axillounilateral femoral grafts.

A total of 130 axillofemoral grafts were peformed in 120 patients from 1966 to present; 66 were axillobilateral femoral moral and 64 were axillounilateral femoral grafts. The average patient age was 66 years. The indications for operation were occlusive disease with rest pain or gangrene in 102 patients, severe claudication four, and bypass of a thoracic aneurysm in one. The one month operative mortality rate was 8 percent (ten patients). Four deaths occurred in elderly patients operated upon as emergencies with acute aortic occlusion. In the 126 elective cases, there were six postoperative deaths (4.7 percent). Twenty thrombectomies were performed in 15 axillobilateral femoral grafts of which 15 (75 percent) were successful. In the unilateral grafts there were 25 thrombectomies in 22 grafts, of which only eight (32 percent) were successful. The 5 year patency rate by the life-table method was 74 percent for axillobilateral femoral grafts and 37 percent for axillounilateral femoral grafts. This difference in patency rates is statistically significant (p < 0.01). Average flow measured by electromagnetic flow meter in six axillobilateral femoral grafts was 621 c.c. per minute and in 11 unilateral femoral grafts was 273 c.c. per minute. We attribute the higher patency rate in axillobilateral femoral grafts to this increased flow. These data indicate that axillobilateral femoral grafts may be performed with anticipation of a 5 year patency rate comparable to that with conventional aortoiliac reconstruction and that axillobilateral femoral grafts should be performed in preference to axillounilateral femoral grafts in poor-risk patients requiring extra-anatomic bypass for aortoiliac occlusive disease.

Aged↗