Biomedical subjects

H Roder

Publications and source records attributed to H Roder.

At least 73 records · Page 4Linked to original sources

PubMed1985

Individual amide proton exchange rates in thermally unfolded basic pancreatic trypsin inhibitor.

A novel experiment is described for measurements of amide proton exchange rates in proteins with a time resolution of about 1 s. A flow apparatus was used to expose protein solutions in 2H2O first to high temperature for a predetermined time period, during which 1H-2H exchange proceeded, and then to ice-water. The technique was applied for exchange studies in thermally unfolded, selectively reduced basic pancreatic trypsin inhibitor. Measurements were made by 1H nuclear magnetic resonance after the exchange was quenched by rapid cooling. Thereby, the sequence-specific resonance assignments for the folded protein could be used, which had been previously obtained. The results of this study indicate that the exchange rates in the thermally unfolded protein are close to those expected for a random chain and that the NH exchange is catalyzed by 2H+ and O2H- up to high temperature, with no significant contributions from p2H-independent catalysis. We conclude that the parameters derived by Molday et al. [Molday, R. S., Englander, S. W., & Kallen, R. G. (1972) Biochemistry 11, 150-158] from measurements with small model peptides can be used to calculate intrinsic exchange rates in unfolded proteins and thus provide a reliable reference for the interpretation of exchange rates measured under native conditions.

Amides↗

PubMed1985

Trans/13-cis isomerization is essential for both the photocycle and proton pumping of bacteriorhodopsin.

We studied an analogue of bacteriorhodopsin whose chromophore is based on all-trans retinal. A five-membered ring was built around the 13-14 double bond so as to prohibit trans to 13-cis isomerization. No light-induced photochemical changes were seen, other than those due to a small amount (approximately 5%) of unbleached bacteriorhodopsin remaining in the apomembrane used for regeneration. The techniques used included flash photolysis at room and liquid nitrogen temperatures and Fourier-transform infrared difference spectroscopy. When the trans-fixed pigment was incorporated into phospholipid vesicles, no evidence of light-initiated proton pumping could be found. The results indicate that trans to 13-cis isomerization is essential for the photochemical transformation and function of bacteriorhodopsin.

Bacteriorhodopsins↗

PubMed1984

Comparison of the magnetic properties of deoxy- and photodissociated myoglobin.

The magnetic susceptibility of photodissociated carbon monoxy myoglobin has been measured over the temperature range from 1.7 to 25 K at 10 and 50 kG with a superconducting susceptometer. The spin and the crystal field parameters of the iron ion were extracted by a spin Hamiltonian approach. Under equivalent conditions the magnetic susceptibility of deoxy myoglobin was measured. In both experiments the CO-bound protein was used as a diamagnetic reference. Above about 5 K the metastable photolysed state and the equilibrium deoxy form of myoglobin are magnetically indistinguishable and can be fitted with S = 2 and g = 2. The transition from spin 0 to spin 2 and the conformational changes known to accompany the electronic change thus also occur after photolysis at low temperature. At temperatures below 5 K, differences become apparent, indicating a somewhat smaller zero-field splitting in the photoproduct as compared to the ligand-free state at equilibrium. In qualitative agreement with observations made by other techniques, the data imply that even at 1.7 K substantial structural relaxation occurs in the heme region of myoglobin after photodissociation. The results are important for the interpretation of the ligand binding kinetics after flash photolysis at low temperature and contribute to the understanding of the relationship between electronic structure and function in heme proteins.

Animals↗

PubMed1983

Nanosecond flash photolysis study of carbon monoxide binding to the beta chain of hemoglobin Zürich [beta 63(E7)His leads to Arg].

Binding of carbon monoxide to beta chains of hemoglobin Zürich has been studied by flash photolysis over the time range of nanoseconds to seconds at temperatures from 20 to 300 K. From 20 to 200 K a single rebinding process (process I) is seen, characterized by a distribution of barrier heights with a peak enthalpy of 2.3 kJ/mol. Above 200 K some ligands escape from the pocket into the matrix, and above 260 K recombination from the solvent sets in. Process I is visible up to 300 K, but above 200 K its rate remains essentially constant at about 4 X 10(8)s -1. Above about 250 K, process I is exponential in time, indicating rapid conformational relaxation. The results are discussed within the framework of a sequential model for ligand binding.

Arginine↗

PubMed1981