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Biomedical subjects

D Magde

Publications and source records attributed to D Magde.

27 records · Page 2Linked to original sources
PubMed1988

Picosecond kinetics of cytochromes b5 and c.

Ligand photolysis and subsequent recombination in cytochromes b5 and c have been studied with picosecond resolution. In both proteins, an iron-histidine bond is broken after excitation with 314-nm light, and recombination occurs with a rate constant of about 1.4 x 10(11) s-1. Photolysis and reformation of the iron-histidine bond may be surprising as these hemoproteins do not reversibly bind ligands in nature. The findings are explained using results both from experiments on model hemes and from computer investigations with atomic resolution on the three-dimensional structure of the protein. After photolysis, the formation and recombination of the geminate contact pair are attributed to simple low amplitude ligand bond rotations, a result that can be applied to geminate processes in other hemoproteins and model heme compounds as well.

Animals↗
PubMed1987

Metal ion binding sites of bacteriorhodopsin. Laser-induced lanthanide luminescence study.

Laser-excited luminescence lifetimes of lanthanide ions bound to bacteriorhodopsin have been measured in deionized membranes. The luminescence titration curve, as well as the binding curve of apomembrane (retinal-free) with Eu3+, has shown that the removal of the retinal does not significantly affect the affinity of Eu3+ for the two high affinity sites of bacteriorhodopsin. The D2O effects on decay rate constants indicate that Eu3+ bound to the high affinity sites of native membrane or apomembrane is coordinated by about six ligands in the first coordination sphere. Tb3+ is shown to be coordinated by four ligands. The data indicate that metal ions bind to the protein with a specific geometry. From intermetal energy transfer experiments using Eu3+-Pr3+, Tb3+-Ho3+, and Tb3+-Er3+, the distance between the two high affinity sites is estimated to be 7-8 A.

Bacteriorhodopsins↗
PubMed1986

Picosecond geminate recombination of nitrosylmyoglobins.

The kinetics of NO geminate recombination to sperm whale and elephant myoglobins has been studied on the picosecond time scale using an amplified colliding-pulse mode-locked ring dye laser. The dynamics of ligand rebinding are shown to be affected by the distal structure of the protein surrounding the heme pocket.

Animals↗
PubMed1985

Geminate recombination of CO in rabbit, opossum, and adult hemoglobins.

The geminate recombination of CO with Hb following dissociation by a 10-ns laser pulse has been studied as a function of pH (9.2 and 7.0 without inositol hexaphosphate and 6.0 with inositol hexaphosphate) and temperature (5-35 degrees C). The hemoglobins studied included adult, Rothschild, rabbit, opossum, and carp. Despite significant differences in their structural and functional properties, the first four of these hemoglobins show similar trends in the yields, rates, and activation energies of the geminate recombination. The nature of the "cage recombination" in hemoglobin is discussed in the light of such findings. Neither a slow diffusion model nor a model based upon a specific non-heme binding site accounts for the observations.

Animals↗
PubMed1984

Geminate recombination in carboxy hemoglobin A and its relation to overall carbon monoxide reactivity.

The geminate recombination of CO with carboxy hemoglobin (Hb4(CO)3) following a ten nanosecond laser pulse and the overall combination of the fourth CO with Hb4(CO)3 has been studied as a function of pH in the presence and absence of inositol hexaphosphate. The results indicate that the kinetics of both reactions are independent of pH and phosphate concentration. The results are discussed in terms of a two-step mechanism: a pre-equilibrium step followed by heme--ligand bond formation. The latter is also known as the geminate recombination reaction (Hb + CO in equilibrium Hb X CO in equilibrium HbCO).

Carbon Monoxide↗
PubMed1983

Fluorescence lifetimes in the bipartite model of the photosynthetic apparatus with alpha, beta heterogeneity in photosystem II.

Recent studies of the lifetime of fluorescence after picosecond pulse excitation of photosynthetic organisms revealed relatively complex decay kinetics that indicated a sum of three exponential components with lifetimes spanning the range from about 0.1-2.5 ns. These fluorescence lifetime data were examined in the context of a simple photochemical model for photosystem II that was used previously to account for fluorescence yield data obtained during continuous illumination. The model, which consists of a single fluorescing species of antenna chlorophyll and a reaction center, shows that, in general, the decay kinetics after pulse excitation should consist of the sum of two exponential decays. The model also shows that in going from open to closed reaction centers the lifetime of fluorescence may increase much more than the yield of fluorescence and surprisingly long fluorescence lifetimes can be obtained. However, conditions can be stated where fluorescence will decay essentially as a single component and with lifetime changes that are proportional to the yield changes. A heterogeneity was also introduced to distinguish photosystem II(alpha) units, which can transfer excitation energy among themselves but not the photosystem I, and photosystem II(beta) units, which can transfer energy to photosystem I but not to other photosystem II units. It is proposed that the rather complex fluorescence lifetime data can be accounted for in large part by the simple photochemical model with the alpha, beta heterogeneity in photosystem II.

Journal Article↗
PubMed1980

Kinetics of ligation reactions of rabbit hemoglobin in quaternary R and T states.

Rabbit hemoglobin shows significantly lower affinity for CO than does human hemoglobin (Hb A). The overall ligand combination and dissociation rate constants reveal, however, only small differences between Hb A rabbit Hb; this is mainly due to the fact that beta chains in rabbit hemoglobin determine the kinetics of ligand dissociation and combination. The heme environment in these chains is probably not very different in rabbit Hb and human Hb A. Rabbit hemoglobin alpha chains, on the other hand, exhibit greatly reduced CO and O2 combination rates in the R state and are primarily responsible for the overall low CO affinity of rabbit Hb. We postulate that the low ligand affinity of alpha chains in rabbit Hb is due to the substitution of larger residues at positions B10(Leu leads to Val), Cd6(Leu leads to Phe), and CD7(Ser leads to Thr). The possible implication of such substitutions for the kinetic and equilibrium properties of rabbit Hb are discussed.

Animals↗