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Biomedical subjects

J Friedrich

Publications and source records attributed to J Friedrich.

At least 109 records · Page 6Linked to original sources
PubMed1985

Chemical modification of cytochrome P-450 LM2 with N-acetylimidazole. Evidence for the functional involvement of tyrosyl residues.

Cytochrome P-450 LM2 has been reacted with N-acetylimidazole. About three tyrosyl residues of cytochrome P-450 LM2 are accessible to O-acetylation. The analysis of the spectral dissociation constants, substrate binding kinetics, reduction kinetics, N-demethylase activity and substrate conversion by artificial oxygen-donating agents of differently acetylated enzyme provides evidence for the existence of two groups of accessible tyrosines. One tyrosyl residue is located in the immediate environment of the heme iron and is involved in the binding of type II substrates. This tyrosine is not necessary for N-demethylation. Acetylation of two further tyrosyl residues, however, causes an almost complete inhibition of enzymatic activity. The results strongly suggest tyrosine(s) to be involved in NADPH-cytochrome P-450 reductase dependent N-demethylation.

Acetylation↗
PubMed1984

Primary structure of human class II histocompatibility antigens. Reversed-phase high-performance liquid chromatography for integral membrane proteins.

The amino acid sequence of the human HLA-DR2 class II antigen was determined with the aid of high-performance liquid chromatography. By applying exclusively Hypersil-ODS as the stationary phase in combination with three buffer systems, the amino acid sequences of the extracellular parts of the DR alpha- and DR beta-chains could be established. Moreover, the sensitivity of the procedure allowed the determination of the primary structures of additional class II polypeptides isolated together with the DR2 alpha- and the DR2 beta-chains. Significant insight into the heterogeneity of class II molecules was thereby obtained. In addition, a simple, rapid and selective method of general applicability is described for the isolation of membrane fragments of integral membrane proteins. Using Sep-Pak cartridges with a mobile phase containing 60% formic acid and varying 1-propanol concentrations, the highly hydrophobic peptides can selectively be separated from the hydrophilic fragments.

Amino Acid Sequence↗
PubMed1984

Chemical modification of tyrosine residues at the active centre of cytochrome P-450 CAM.

Soluble cytochrome P-450 CAM from Pseudomonas putida (EC 1.14.14.1) was chemically modified with tetranitromethane. At least five out of totally nine tyrosine residues are accessible to nitration as shown by tryptic peptide mapping using HPLC. Modification in the presence of the inhibitor metyrapone and subsequent peptide mapping indicate the location of one tyrosine residue at the active centre of cytochrome P-450 CAM.

Aryl Hydrocarbon Hydroxylases↗
PubMed1983

Modification of cytochrome P-450 with fluorescein isothiocyanate.

Fluorescein isothiocyanate (FITC) has been shown to be selectively attached to the N-terminus of cytochrome P-450 LM2. The N-demethylase activity of cytochrome P-450 LM2 reconstituted systems modified in this way was inhibited by 25%. As revealed by CD measurements the overall conformation as well as the immediate heme environment of cytochrome P-450 LM2 remained unchanged after attachment of the FITC molecule. The binding affinity of modified cytochrome P-450 LM2 toward benzphetamine and aniline and the cumene hydroperoxide- or H2O2-supported N-demethylation of benzphetamine are maintained. However, the introduction of the electron via NADPH-cytochrome P-450 reductase (EC 1.6.2.4) is impaired after modification of the alpha-amino group. The extent of reduced modified cytochrome P-450 LM2 in the cytochrome P-450 reductase-supported reduction reaction is diminished and the half-time of the reduction is increased. The diminished reducibility is ascribed to steric hindrance of groups directly involved in the interaction between cytochrome P-450 LM2 and NADPH-cytochrome P-450 reductase or to blocking of the charge-pair interactions between the alpha-amino group of P-450 LM2 and the respective negatively charged group of NADPH-cytochrome P-450 reductase. By energy-transfer measurements distances between the heme and the alpha-amino group of 2.65 and 3.97 nm for the oligomeric and the monomeric forms of P-450 LM2, respectively, have been determined.

Animals↗
PubMed1979

Comparison of spectral properties of 3-MC induced cytochrome P-448 from rabbits and rats.

EPR and optical spectral properties of cytochrome P-488 from 3-methylcholanthrene-induced rabbits are compared with those of rats. In the EPR spectra at 77K and in the optical absorption spectra at room temperature a considerable temperature independent high spin content of the rabbit cytochrome is observed which has been estimated to about 55% by titration with n-octylamine. On the other hand the high spin content of the rat cytochrome depends strongly on temperature and amounts to about 6% at 5 degrees C and to about 35% at 34 degrees C. The binding of substrates and ligands to the rabbit cytochrome as well as its reduction by sodium dithionite are slower as compared with the rat cytochrome but also with phenobarbital-induced cytochrome P-450 from rats and rabbits. Contrary to the 3-methylcholanthrene induced cytochrome P-448 from rats, that from rabbits does not bind 3-methylcholanthrene. A particular protein structure establishing the high spin state and an absent binding site for type I substrates is assumed to be responsible for these and other peculiarities of cytochrome P-448 from 3-methylcholanthrene-induced rabbits.

Animals↗
PubMed1979

Quantum chemical interpretation of the spectral properties of the CO and O2 complexes of hemoglobin and cytochrome P-450.

The electronic transitions of CO and O2 complexes of hemoglobin and cytochrome P-450 were calculated using a PPP method extended for metal complexes. The calculations show that the unusual spectral properties of cytochrome P-450 are very sensitive to the iron-sulfur bond distance. It is suggested from these calculations that for the conversion of cytochrome P-450 to cytochrome P-420 an increase of the iron-sulfur bond distance of only about 0.2 A is sufficient. The anomalous Soret band of the CO complex as well as the normal Soret band of the O2 complex of cytochrome P-450 are explicable assuming a mercaptide sulfur as fifth ligand.

Animals↗
PubMed1977

[Modern serology of rheumatic fever and glomerulonephritis (author's transl)].

For the assessment of the situation after streptococcal infection and thus for prevention of rheumatic fever and glomerulonephritis more simple and rapid serological tests are needed. The principle of indirect haemagglutination seems particularly suited for this purpose. A rapid slide test (streptozyme) for the simultaneous detection of antibodies against five streptococcal enzymes in capillary blood or serum was compared to four monospecific tests: latex-Asl, Antistreptolysin-O (ASL-O), antistreptokinase and anti NADase. Several lots of test kits and more than four hundred sera of adults and children with and without suspected rheumatic fever were tested. The number of falsely negative and falsely positive results was small as compared to single monospecific tests. Additional positive reactions were obtained when the ASL-O was within the normal range, but the titer against several exoenzymes were elevated, or, when the antibodies against a single exoenzyme were extremely strong. The precision of the polyvalent test may not be quite as high as if three monospecific tests are applied, It is however sufficient. Thus it seems unrealistic to require the performance of at least three monospecific tests under the present epidemiological conditions.

Antibodies↗