Biomedical subjects

Christel Hempen

Publications and source records attributed to Christel Hempen.

3 recordsLinked to original sources

PubMed2005

Analysis of microperoxidases using liquid chromatography, post-column substrate conversion and fluorescence detection.

A liquid chromatographic method with on-line activity determination for microperoxidases has been developed. After enzymatic digestion of a cytochrome, possibly under formation of microperoxidases, the product mixture is separated by reversed-phase liquid chromatography. The products first pass a diode-array detector, and are then subjected to a reaction with 4-(N-methylhydrazino)-7-nitro-2,1,3-benzooxadiazole (MNBDH) and hydrogen peroxide. In a reaction coil, microperoxidases catalyze the reaction under formation of the fluorescent 4-(N-methylamino)-7-nitro-2,1,3-benzooxadiazole (MNBDA). Quantification of the microperoxidases is performed using a fluorescence detector at an excitation wavelength of 470 nm and an emission wavelength of 545 nm, respectively. For this LC-based detection system, limits of detection are 3 x 10(-8) mol/L, limits of quantification are 9 x 10(-8) mol/L, and a linear range from 9 x 10(-8) mol/L to 3 x 10(-6) mol/L is obtained for the microperoxidases MP-9 and MP-11. A highly active microperoxidase MP-6 was found in the reaction of cytochrome c from bovine heart with protease from streptomyces griseus.

Animals↗

PubMed2005

Labeling strategies for bioassays.

Different labeling strategies for enzymatic assays and immunoassays are reviewed. Techniques which make use of direct detection of a label, e.g. radioimmunoassays, are discussed, as are techniques in which the label is associated with inherent signal amplification. Examples of the latter, e.g. enzyme-linked immunosorbent assays or nanoparticle-label based assays, are presented. Coupling of the bioassays to chromatographic separations adds selectivity but renders the assays more difficult to apply. The advantages and drawbacks of the different analytical principles, including future perspectives, are discussed and compared. Selected applications from clinical, pharmaceutical, and environmental analysis are provided as examples.

Fluorescent Dyes↗

PubMed2005

Liquid chromatographic/mass spectrometric investigation on the reaction products in the peroxidase-catalyzed oxidation of o-phenylenediamine by hydrogen peroxide.

Mass spectrometric evidence was obtained to confirm that the main reaction product of the horseradish peroxidase (POD)-catalyzed oxidation of o-phenylenediamine (OPD) by hydrogen peroxide is 2,3-diaminophenazine. Although this reaction is one of the most widespread detection schemes in enzyme-linked immunosorbent assays (ELISAs), the literature data on the identity of the reaction product(s) have been strongly contradictory throughout the last few decades. Liquid chromatography with UV/Vis and mass spectrometric detection as well as exact mass measurements after LC fraction collection have led to the unambiguous identification of 2,3-diaminophenazine as main reaction product. 2,2'-Diaminoazobenzene, which is frequently described in other publications to be the major reaction product, was not detected at all.

Catalysis↗