MAO
Monoamine Oxidase. A flavin-containing enzyme located on the outer membrane of the mitochondria. There are two forms of monoamine oxidase (MAO A and MAO B), both of which are involved in the Phase I biotransformation of certain drugs.
MDR
Multi-Drug Resistance
mechanism-based inhibition
Often used to refer to any irreversible or quasi-irreversible metabolism-dependent inhibition caused by substrates that are converted to one or more products that immediately and irreversibly inactivate the enzyme and do not leave the active site during catalysis by the enzyme. By definition, mechanism-based inhibition
excludes the formation of metabolites that are simply more potent direct-acting inhibitors than the parent.
The total fate of a xenobiotic, which includes: absorption, distribution, biotransformation, metabolism and elimination (ADME). Metabolism and biotransformation are often used interchangeably, but the latter term does not encompass absorption, distribution and elimination.
includes both mechanism-based inhibition and also the formation of metabolites that are more potent direct-acting inhibitors than the parent (
i.e., reversible metabolism-dependent inhibition).
microsomes
Vesicles derived from the endoplasmic reticulum, which contain cytochrome P450 enzymes that are responsible for many phase I biotransformation reactions. Microsomes are isolated by ultracentrifugation (104,000 g for one hour) of the postmitochondrial (S9) fraction.
mitochondria
Organelles that synthesize ATP and largely determine cellular respiration rate. This subcellular fraction is well suited for determining the metabolism of certain xenobiotics by such mitochondrial enzymes as monoamine oxidase (MAO), rhodanese,
N-acyltransferase and aldehyde dehydrogenase.
monoclonal
Antibodies that are identical because they were produced by one type of immune cell and are all clones of a single parent cell.
mRNA
Messenger Riboneucleic Acid (mRNA) is a molecule of RNA encoding a chemical "blueprint" for a protein product. Branched DNA assays can be used to detect the presence of mRNA.