Biomedical subjects

Nektaria Markoglou

Publications and source records attributed to Nektaria Markoglou.

3 recordsLinked to original sources

PubMed2004

Immobilized enzyme reactors based upon the flavoenzymes monoamine oxidase A and B.

Monoamine oxidase (MAO) catalyzes the oxidative deamination of amines. The enzyme exists in two forms, MAO-A and MAO-B, which differ in substrate specificity and sensitivity to various inhibitors. Membrane fractions containing either expressed MAO-A or MAO-B have been non-covalently immobilized in the hydrophobic interface of an immobilized artificial membrane (IAM) liquid chromatographic stationary phase. The MAO-containing stationary phases were packed into glass columns to create on-line immobilized enzyme reactors (IMERs) that retained the enzymatic activity of the MAO. The resulting MAO-IMERs were coupled through a switching valve to analytical high performance liquid chromatographic columns. The multi-dimensional chromatographic system was used to characterize the MAO-A (MAO-A-IMER) and MAO-B (MAO-B-IMER) forms of the enzyme including the enzyme kinetic constants associated with enzyme/substrate and enzyme/inhibitor interactions as well as the determination of IC(50) values. The results of the study demonstrate that the MAO-A-IMER and the MAO-B-IMER can be used for the on-line screening of substances for MAO-A and MAO-B substrate/inhibitor properties.

Bioreactors↗

PubMed2002

Biosynthesis in an on-line immobilized-enzyme reactor containing phenylethanolamine N-methyltransferase in single-enzyme and coupled-enzyme formats.

An immobilized-enzyme reactor (IMER) based upon phenylethanolamnie N-methyltransferase (PNMT) has been developed. The activity of the PNMT-IMER and its applicability for on-line N-methylation of normetanephrine was investigated. The reactor was connected through a switching valve to a cyano (CN) and ODS stationary phase connected in series. The substrate was injected onto the PNMT-IMER and the unreacted substrate and product were eluted and transported via a switching valve onto the analytical columns. The results from the PNMT-IMER/CN-ODS chromatographic system demonstrate that the enzyme retained its catalytic activity. Known substrates and inhibitors for PNMT were examined and the chromatographic system was utilized to carry out both quantitative and qualitative determinations. The PNMT-IMER/ CN-ODS system proves to be useful in basic biochemical studies, an ideal for the high throughput screening of substances for PNMT substrate-inhibitor properties. The PNMT-IMER was then coupled in series using switching-valve technology with a previously developed dopamine beta-hydroxylase immobilized-enzyme reactor and used to carry out the on-line two-step synthesis of epinephrine from dopamine.

Animals↗

PubMed2002

On-line synthesis utilizing immobilized enzyme reactors based upon immobilized dopamine beta-hydroxylase.

Immobilized enzyme reactors (IMERs) based upon dopamine beta-hydroxylase (DBH) have been developed. Immobilized artificial membrane (IAM) and glutaraldehyde-P (Glut-P) stationary phases have been used to immobilize DBH. When DBH is immobilized on the Glut-P interphase the enzyme is outside the stationary phase whereas with the IAM interphase the enzyme is embedded within the interphase surroundings. The activity of each IMER and their ability for on-line hydroxylation has been investigated. The resulting IMERs are enzymatically active and reproducible. The IMERs can be utilized through the use of coupled chromatography to characterize the cytosolic (DBH-Glut-P-IMER) and membrane-bound (DBH-IAM-IMER) forms of the enzyme. The substrate is injected onto the individual IMERs and the reactants and products are eluted onto a phenylboronic acid column for on-line extraction. The substrates and products are then transported via a switching valve to coupled analytical columns. The results demonstrate that enzyme-substrate and enzyme-inhibitor interactions can be investigated with the on-line system. These IMERs can be utilized for the discovery and characterization of new drug candidates specific for the soluble form and membrane-bound form of DBH. The effects of flow-rate, contact time, pH and temperature have also been investigated.

Animals↗