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Biomedical subjects

J C Chien

Publications and source records attributed to J C Chien.

At least 19 recordsLinked to original sources
PubMed1996

Differential regulation of trichome formation on the adaxial and abaxial leaf surfaces by gibberellins and photoperiod in Arabidopsis thaliana (L.) Heynh.

In wild-type (WT) Columbia and Landsberg erecta ecotypes of Arabidopsis thaliana (L.) Heynh., trichomes are present on the adaxial surfaces of all rosette leaves but are absent from the abaxial surfaces of the first-formed leaves. We have determined that both long-day (LD) photoperiod and gibberellin (GA) stimulate trichome formation. WT plants grown in LD conditions produce the first abaxial trichome on earlier leaves than plants grown in short-day (SD) conditions. Photoperiod sensitivity of abaxial trichome formation on WT plants develops gradually over time, reaching the maximum sensitivity about 24 d after germination. Application of gibberellic acid to WT plants growing in SD conditions accelerates the onset of abaxial trichomes. Conversely, application of 20 to 80 mg L-1 paclobutrazol, a GA biosynthesis inhibitor, to wild-type plants suppresses trichome initiation on the abaxial epidermis. The GA-deficient mutants ga1-5 and ga4-1 and the GA-insensitive mutant gai-1 exhibit delayed onset of abaxial trichomes when grown in LD conditions. The null mutant ga1-3 produces completely glabrous leaves when grown in SD conditions. Application of gibberellic acid to glabrous ga1-3 plants consistently induces earlier formation of trichomes on the adaxial epidermis than on the abaxial epidermis, demonstrating a difference between the adaxial and abaxial surfaces in their response to GA with regard to trichome formation.

Arabidopsis↗
PubMed1983

Structural dynamics of human deoxyhemoglobin and hemochrome investigated by nuclear gamma resonance absorption (Mössbauer) spectroscopy.

Mössbauer spectra of human deoxyhemoglobin and hemochrome frozen solutions, selectively enriched with 57Fe in either the alpha chains or the beta chains, were measured from 4.2 to 250 K. The Lamb-Mössbauer factor, ln f = 4II2 [x2]gamma/lambda 2, was calculated from these spectra and gives the structural dynamics of the iron atom (heme). Large differences in the mean-squared displacement, [x2]gamma, of the heme between hemochrome and deoxyhemoglobin at temperatures above 210 K were observed, demonstrating that when iron is bound to a rigid part of the protein (i.e., distal histidine in hemochrome), motions of the heme are suppressed (i.e., the dynamics are decreased). Comparison of the motions of these two hemoglobins proves that molecular diffusion can be neglected in an analysis of the dynamics below approximately 250 K.

Hemeproteins↗
PubMed1982

Electron paramagnetic resonance crystallography of bacterial catalase: g-Contour mapping method of analysis.

Single crystals of bacterial catalase from Micrococcus luteus have been examined by EPR at 77 K. X-ray perfect crystals gave a set of four prominent resonances in all three orthogonal planes which yielded eight heme direction cosine matrices to an accuracy of +/- 2 degrees as expected for the P4(2)2(1)2 space group and unit cell parameters previously determined. These matrices are related by D4 symmetry operation of the space group. There were additional weaker resonances only resolved in two or even one plane. A method of g-contour mapping was devised to solve for the orientations of hemes that give rise to these weaker resonances. Three additional sets of heme orientations, also following D4 symmetry, were determined. All of the above sites have the same principal g values, 2.0, 5.4, and 6.6. The EPR crystallographic results imply that several conformational substates may be trapped at 77 K.

Catalase↗
PubMed1980

Carp hemoglobin. I. Precise oxygen equilibrium and analysis according to the models of Adair and of Monod, Wyman, and Changeux.

Precise oxygen equilibria for carp hemoglobin had been measured from about 1% to 99% saturation at 15 degrees C. The determinations were made in 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol buffer and in phosphate buffer in the presence and absence of P6-inositol (IHP). At the highest cooperativity, carp hemoglobin has a maximum Hill coefficient, n, of 2.3 and free energy of interaction, delta GI, of 2100 cal/site; addition of IHP decreases these values to 1.6 and 1640 cal/site, respectively. NaCl at 0.1 M or 0.2 M increases both delta GI and n. Intrinsic association constants, ki, were estimated by nonlinear least square fit of Hill plots; their values are more sensitive to pH than normal adult human hemoglobin (HbA). Identical values of nmax and ki were obtained with either one of the two major components of carp hemoglobin as with the hemolysate under the same conditions. IHP, whose effect on carp hemoglobin is much smaller than that on HbA, alters all ki values rather indiscriminately. Since IHP affects k4, it binds to Hb(O2)3 as well as the lower oxygenated species. The same is true for inorganic phosphate at pH < 8.3; however, above this pH, the phosphate ion is apparently expelled when the third heme is oxygenated since addition of PO(3-)4 does not change k4. From the intrinsic association constants, one concludes that carp hemoglobin in the cooperative regime undergoes allosteric transition after oxygenation of the third heme. Lowering of cooperativity by pH changes seems to shift conformational transitions to earlier stages of oxygenation. Parameters of the Monod, Wyman, and Changeux model were estimated by a similar nonlinear least square procedure. In the phosphate system, values of KR, c, and L are found to be 8.2 mm Hg-1, 1.3 x 10(-2), and 4.2 x 10(6) at pH 7.20. Changes of pH in either direction increases the values of KR and L and decreases the c value negating assumptions for pH-independent T and R quaternary structures.

Animals↗
PubMed1980

Carp hemoglobin. II. The alkaline Bohr effect.

The Bohr effect of carp hemoglobin has been determined by differential titration, by direct acid-base titration, and by calculation from precise oxygen equilibrium data over a wide pH variation. The results for the hemolysate and the two major components are essentially identical. At pH 6.9 in the vicinity of maximum cooperativity and maximum Bohr effect, the protein releases 3.7 protons in the absence of added ions. This Bohr curve above pH 7 is not changed by the presence of 0.05 M 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol (bis-Tris) buffer, but is changed below the pK of the bis-Tris amine, giving a maximum of 4.3 protons at pH 6.65. In 0.1 M phosphate, the maximum is increased to 6.1 protons and is shifted to pH 7.25. Addition of 1.4 mM P6-inositol lowers the magnitude of the Bohr effect and shifts its maximum to an even higher pH. At the limit of high pH (9.02), without buffer or in bis-Tris, there is a net uptake of about 0.5 proton upon oxygenation. The average heat of ionization of the Bohr groups is 5500 +/- 800 cal. Even though chloride ion has a pronounced effect on the oxygenation properties of carp hemoglobin, it has a small influence on the Bohr effect up to 0.5 M NaCl. In 5 M NaCl, the magnitude of the Bohr effect is reduced by approximately 30%., Acid base titrations give three to four oxygen-linked groups for carp hemoglobin in water; this is increased to about six groups in 2.5 M NaCl. The results suggest that carp hemoglobin is functionally versatile and may provide one way to regulate its CO2 transport via heterotropic allosteric interactions. In phosphate buffer at the pH value where carp hemoglobin is strongly cooperative, the proton release is linear with respect to ligand saturation. Lowering the cooperativity by either an increase or decrease in pH results in nonlinear relationships.

Animals↗
PubMed1980

Nuclear magnetic resonance studies of the phenylalanine residues of eukaryotic cytochrome c.

The resonances of Phe 82 and Phe 10 in the nuclear magnetic resonance spectra of horse cytochrome c are reassigned using nuclear Overhauser enhancements. The reassignments provide new information about the oxidation state linked conformation change of cytochrome c. The region of the protein now known to be affected by the change extends to the part of the protein close to Phe 10.

Animals↗
PubMed1980

Electron paramagnetic resonance crystallography of 17O-enriched oxycobaltomyoglobin: stereoelectronic structure of the cobalt dioxygen system.

An electron paramagnetic resonance crystallographic study was made on oxycobaltomyoglobin with the dioxygen ligand enriched to 19.1% in (17)O. There are two spectroscopically distinct cobalt dioxygen species. The less abundant species, II (40%), has nonequivalent oxygen atoms with superhyperfine tensors (O)A(alpha) = (5, -67.5, 22.4)G and (O)A(beta) = (5.4, -83.3, 30.3)G. Together with the previously reported (59)Co hyperfine tensor [Chien, J. C. W. & Dickinson, L. C. (1972) Proc. Natl. Acad. Sci. USA 69, 2783-2787], the orbital spin densities are found to be O(alpha)(p(eta)) = 0.48, O(alpha)(p(zeta)) = -0.11, O(beta)(p(eta)) = 0.74, O(beta)(p(zeta)) = -0.16, Co(d(xz)) = -0.01, Co(d(yz)) = 0.06 for a total electron density of 1.01. The O-O axis is directed toward His-E7, suggesting a possible hydrogen bonding interaction which may contribute to the nonequivalency of the oxygen atoms; its projection approximately bisects N(1)-Fe-N(2). The z axis of the (Co)A tensor is tilted at an angle of 28 degrees from the heme normal, resulting in a Co-O-O angle of 120 degrees . The more abundant species, I (60%), has equivalent oxygen atoms with (O)A(gamma) = (12, -72.5, 20)G and orbital spin densities of O(gamma)(p(eta)) = 0.54, O(gamma)(p(zeta)) = -0.05, Co(d(xz)) = -0.02, Co(d(yz)) = 0.09 for a total spin density of 1.10. Although the direction cosines for this molecule cannot be precisely determined, the projection of its O-O axis approximately bisects N(2)-Fe-N(3) and is parallel to the imidazole ring of His-F8. Increase of temperature changes g, (Co)A, and (O)A values, with the largest effect seen with (O)A. This temperature dependence indicates averaging of the two bond structures which are stabilized at 77 K.

Animals↗
PubMed1979

Carp hemoglobin. V. Effects of pH and P6-inositol on autooxidation.

Autooxidation of carp hemoglobin has been measured from 4--25 degrees C with and without P6-inositol. The rate was accelerated by the increase of proton concentration and/or the addition of P6-inositol. As the rate increases the kinetics become more complex. In acidic media with P6-inositol, the autooxidation is initially rapid which becomes slower subsequently but eventually proceeds very fast. The activation energy for autooxidation is about 19 kcal. mol-1. The complicated kinetics are partly attributable to the fact that carp hemoglobin is incompletely oxygenated under these conditions and that various liganded molecules including partially oxidized species have different susceptibilities toward autooxidation.

Animals↗
PubMed1978

Reduction of methemoglobin by cobaltocytochrome c catalyzed by mediators.

The reduction of methemoglobin by cobaltocytochrome c (Cocyt c) has been measured using nine mediators of different half-reduction potentials, Em, 7. The rate increases with the increase of Em, 7 for the mediator but dropped precipitously when it becomes more positive than the Em, 7 for the methemoglobin/hemoglobin couple. The reaction is most efficient with phenzaine methosulfate, therefore it was studied in detail. The reaction is first order in the concentrations of Cocyt c and phenazine methosulfate. The average second-order rate constant for Cocyt c + phenazine methosulfate (M) k1 leads to Cocyt c+ M-. is 2.9 x 10(4) M-1 s-1 at 25 degrees C, 0.1 M phosphate pH 7.0. There is a slight negative temperature dependence of k1 at low temperature; at higher temperatures the process has deltaH not equal to approximately 27 kJ mol-1 and deltaS not equal to approxmately - 75 J mol-1 K-1. The effect of anions reflects the dependence of Em, 7 for the methemoglobin/hemoglobin couple with various anions. There is no significant effect on k1 by the addition of inositol hexakisphosphate. The variation of k1 with pH is complicated. The experimental rate constants are compared with values calculated with the theory of nonadiabatic multiphonon process of electron tunneling.

Azides↗
PubMed1978

Ferricytochrome c oxidation of cobaltocytochrome c. Comparison of experiments with electron-transfer theories.

Electron transfer from cobaltocytochrome c to ferricytochrome c has been studied by stopped-flow kinetics. The second-order rate constant at pH 7.0, 0.1 ionic strenght, 0.2 M phosphate, and 25 degrees C is 8.3 x 103 M-1 s-1. The activation parameters obtained from measurements made between 20 and 50 degrees C are deltaHnot equal to = 2.3 kcal mol-1 and deltaSnot equal to = -33 eu. The rate constant is not significantly dependent on ionic strength; it is also relatively independent of pH between the pK values for conformation transitions. The rate diminishes at pH greater than 12. The self-exchange reaction of cobalt cytochrome c was investigated with pulsed Fourier transform 1H NMR. The rate is too slow on the 1H NMR scale; it is estimated to be less than 133 M-1 s-1. These results together with the self-exchange rates of iron cytochrome c [Gupta, R.K., Koenig, S. H., and Redfield, A. G. (1972), J. Magn. Reson. 7, 66] were analyzed by theories of Jortner and Hopfield. The theories predict the self-exchange of Cocyt c to be too slow for 1H NMR determination. The rate constant calculated by the nonadiabatic multiphonon electron-tunneling theory for the Fecyt c-Fecyt c+ and Cocyt c-Fecyt c+ electron transfers are in good agreement with experiments.

Animals↗
PubMed1977

Manganese cytochrome c. Structure and properties.

Oxidized and reduced manganese cytochromes c, Mn Cyt c+ and Mn Cyt c, have been synthesized. Mn Cyt c+ and Fe Cyt c+ have identical electrophoretic and ion exchange mobilities. Mn Cyt c+ does not bind F-, CN-, or N3- ions; Mn Cyt c does not bind CO or O2. Mn Cyt c is very rapidly autooxidized by O2 even at -50 degrees. The manganese ion is readily dissociated from Mn Cyt c at acidic pH values. Both Mn Cyt c and Mn Cyt c+ are high spin complexes with 3d5 S = 5/2 and 3d4 S = 2 electronic configurations, respectively. The epr spectrum of Mn Cyt c is rhombic with (formula: see text). Both oxidized and reduced Mn Cyt c react with NO; the former reaction is reversible and the product has the following epr spectral parameters: (formula: see text). There is no superhyperfine interaction observable with the NO ligand, and the unpaired electron density is estimated to be mostly in the metal ion d xy orbital. The structure is best formulated as Mn Cyt c (NO)+. The half-reduction potential of Mn Cyt c is + 60 +/- 40 mV. It is neither oxidized by cytochrome oxidase nor reduced by NADH, NADPH, or succinate cytochrome reductase. These physical, chemical, and enzymic properties of manganese cytochromes c suggest a five-coordinate metalloporphyrin prosthetic group with the manganese ion situated significantly out-of-plane toward the side of His-18.

Cytochrome c Group↗