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Biomedical subjects

A Lanir

Publications and source records attributed to A Lanir.

At least 55 records · Page 3Linked to original sources
PubMed1978

Direct observation of the methionine residues of cytochrome c by 13C nuclear magnetic resonance spectroscopy.

The two Cepsilon-methyl methionine groups in cytochrome c have been chemically enriched (45%) with 13C. Their 13C NMR signals have been monitored in both the oxidized and reduced states and under various solution conditions. Methionine residue 80 showed characteristic chemical shift positions for the reduced Fe(II) and cyano-Fe(III) forms. No signal for methionine 80 was observed in the oxidized Fe(III) form due to the paramagnetic effect of the iron atom to which it is bonded, but the position of the methionine 65 signal was shifted, indicating that it is sensitive to the change of oxidation state. Two well resolved signals were observed at pH 11 for the Fe(III) form but only one was resolved at pH 2, indicating that while methionine 80 is definitely displaced from the iron atom at alkaline pH, it may not be in acid conditions.

Cytochrome c Group↗
PubMed1977

Electron spin relaxation time of Fe(III) in high spin heme proteins.

The electron spin relaxation time of high spin Fe(III), taus, was determined from the frequency dependence (5-100 MHz) of the longitudinal proton relaxation rates of water in solutions of catalase, metmyoglobin and acid ferricytochrome c. In all three high-spin heme proteins the relaxation rates incrased below 25 MHz, while no frequency dependence was observed above that frequency. The results are interpreted by assuming that taus, which modulates the dipolar interaction between the unpaired electrons of the iron and the water protons, is frequently independent. Its value was determined to be (6 +/- 1) - 10(-11) s.

Animals↗
PubMed1976

A nuclear magnetic resonance study of the heme environment in beef liver catalase.

The effect of high-spin heme iron in beef liver catalase on the longitudinal and transverse proton relaxation rates of the solvent has been used to probe the environment of the paramagnetic center. The longitudinal proton relaxation rates were measured as a function of temperature (5-31 degrees C), frequency (5-100 MHz), and pH. T1p was found to be pH independent in the range 6-11, indicating that no significant difference occurs in the heme surrounding within this pH range. The ligands formate and acetate, which preserve the spin state of the heme iron upon ligation, displace a water molecule from the sixth coordination position. This reaction is pH independent, while the binding measured by optical spectroscopy is pH dependent. The electron methanol and ethanol essentially do not change the proton relaxation rates. The temperature and frequency dependencies indicate that the relaxation times are governed by the electronic relaxation time of the high-spin ferric iron tau s. Tau s, which was found to be frequency independent, could not be determined from the T1p/T2p ratio, but only from the frequency dependence of the longitudinal relaxation rate at low frequencies. The results of the least-squares fit of the data to the theory indicate that there is one iron-bound rapidly exchanging water molecule. For the Fe3+ ion it was determined that tau s = 7 x 10(-11) s.

Animals↗
PubMed1975

Temperature and requency dependence of solvent proton relaxation rates in solutions of manganese(II) carbonic anhydrase.

Longitudinal and transverse proton relaxation rates of water in solutions of manganese(II) bovine carbonic anhydrase have been measured by pulsed nuclear magnetic resonance spectrometry as a function of temperature (2-35 degrees), frequently (5-100 MHz) and pH. The pH dependence of the longitudinal relaxation rate was fitted to a sigmoidal curve with a pK value at 7.8, while the esterase activity of the manganese(II) enzyme in the hydrolysis of p-nitrophenyl acetate revealed an inflection point at pK = 8.2. The hydration number of manganese(II) carbonic anhydrase could be derived using either the frequency dependence of T1p or the T1p/T2p ratio at only one (high) frequency. Both treatments are in agreement with a model in which one water molecule is bound to the metal at high pH. At low pH the relaxation data imply that no-H20 exists in the first coordination sphere of the manganese ion. The various parameters which are responsible for the proton relaxation mechanisms have been evaluated and are compared to other manganese(II) enzyme systems. The pH dependence of the binding constant of manganese to apocarbonic anhydrase is also reported.

Animals↗