Question: What is detected by the HVA metabolite, produced by the organic chemical of the catecholamine and phenethylamine families?

Context paragraphs:
Dopamine: Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is an organic chemical of the catecholamine and phenethylamine families that plays several important roles in the brain and body.  It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA, which is synthesized in the brain and kidneys.  Dopamine is also synthesized in plants and most animals.

Metabolome: The metabolome refers to the complete set of small-molecule chemicals found within a biological sample.  The biological sample can be a cell, a cellular organelle, an organ, a tissue, a tissue extract, a biofluid or an entire organism.  The small molecule chemicals found in a given metabolome may include both endogenous metabolites that are naturally produced by an organism (such as amino acids, organic acids, nucleic acids, fatty acids, amines, sugars, vitamins, co-factors, pigments, antibiotics, etc.) as well as exogenous chemicals (such as drugs, environmental contaminants, food additives, toxins and other xenobiotics) that are not naturally produced by an organism.  In other words, there is both an endogenous metabolome and an exogenous metabolome.  The endogenous metabolome can be further subdivided to include a "primary" and a "secondary" metabolome (particularly when referring to plant or microbial metabolomes).  A primary metabolite is directly involved in the normal growth, development, and reproduction.  A secondary metabolite is not directly involved in those processes, but usually has important ecological function.  Secondary metabolites may include pigments, antibiotics or waste products derived from partially metabolized xenobiotics.  To qualify as a metabolite, or to be considered to be part of the metabolome, a small molecule must typically have a molecular weight <1500 Da.  This means that molecules such as glycolipids, polysaccharides, short peptides (<14 amino acids) and small oligonucleotides (<5 bases) can be regarded as metabolites or constituents of the metabolome.  On the other hand, very large macromolecules such as proteins, messenger RNA, ribosomal RNA, microRNA and DNA are definitely not metabolites and are not considered to be part of the metabolome.  The study of the metabolome is called metabolomics.  See Figure 1 for a picture of the relationship between different “omes”.

Homovanillic acid: Homovanillic acid (HVA) is a major catecholamine metabolite that is produced by a consecutive action of monoamine oxidase and catechol-O-methyltransferase on dopamine.  Homovanillic acid is used as a reagent to detect oxidative enzymes, and is associated with dopamine levels in the brain.

Phenylethanolamine: Phenylethanolamine (sometimes abbreviated PEOH), or β-hydroxyphenethylamine, is a trace amine with a structure similar to those of other trace phenethylamines as well as the catecholamine neurotransmitters dopamine, norepinephrine, and epinephrine.  As an organic compound, phenylethanolamine is a β-hydroxylated phenethylamine that is also structurally related to a number of synthetic drugs in the substituted phenethylamine class.  In common with these compounds, phenylethanolamine has strong cardiovascular activity and, under the name "Apophedrin", has been used as a drug to produce topical vasoconstriction.

Small Molecule Pathway Database: The Small Molecule Pathway Database (SMPDB) is a comprehensive, high-quality, freely accessible, online database containing more than 600 small molecule (i.e. metabolic) pathways found in humans.  SMPDB is designed specifically to support pathway elucidation and pathway discovery in metabolomics, transcriptomics, proteomics and systems biology.  It is able to do so, in part, by providing colorful, detailed, fully searchable, hyperlinked diagrams of five types of small molecule pathways: 1) general human metabolic pathways; 2) human metabolic disease pathways; 3) human metabolite signaling pathways; 4) drug-action pathways and 5) drug metabolism pathways.  SMPDB pathways may be navigated, viewed and zoomed interactively using a Google Maps-like interface.  All SMPDB pathways include information on the relevant organs, subcellular compartments, protein cofactors, protein locations, metabolite locations, chemical structures and protein quaternary structures (Fig. 1).  Each small molecule in SMPDB is hyperlinked to detailed descriptions contained in the HMDB or DrugBank and each protein or enzyme complex is hyperlinked to UniProt.  Additionally, all SMPDB pathways are accompanied with detailed descriptions and references, providing an overview of the pathway, condition or processes depicted in each diagram.  Users can browse the SMPDB (Fig. 2) or search its contents by text searching (Fig. 3), sequence searching, or chemical structure searching.  More powerful queries are also possible including searching with lists of gene or protein names, drug names, metabolite names, GenBank IDs, Swiss-Prot IDs, Agilent or Affymetrix microarray IDs.  These queries will produce lists of matching pathways and highlight the matching molecules on each of the pathway diagrams.  Gene, metabolite and protein concentration data can also be visualized through SMPDB's mapping interface.

Metabolite: Metabolites are the intermediates and products of metabolism.  The term "metabolite" is usually restricted to small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, catalytic activity of their own (usually as a cofactor to an enzyme), defense, and interactions with other organisms (e.g. pigments, odorants, and pheromones).  A primary metabolite is directly involved in normal "growth", development, and reproduction.  Ethylene is an example of a primary metabolite produced in large-scale by industrial microbiology.  A secondary metabolite is not directly involved in those processes, but usually has an important ecological function.  Examples include antibiotics and pigments such as resins and terpenes etc.  Some antibiotics use primary metabolites as precursors, such as actinomycin which is created from the primary metabolite, tryptophan.  Some sugars that are metabolites; example: fructose or glucose in the metabolic pathways.

Norepinephrine: Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as a hormone and neurotransmitter.  The name "noradrenaline," derived from Latin roots meaning "at/alongside the kidneys," is more commonly used in the United Kingdom; in the United States, "norepinephrine," derived from Greek roots having that same meaning, is usually preferred.  "Norepinephrine" is also the international nonproprietary name given to the drug.  Regardless of which name is used for the substance itself, parts of the body that produce or are affected by it are referred to as noradrenergic.

4-Phenyl-4-(1-piperidinyl)cyclohexanol: 4-Phenyl-4-(1-piperidinyl)cyclohexanol, also known as PPC, is an organic chemical which is a metabolite of phencyclidine (PCP).  It can be detected in the hair of PCP users.

IUPAC nomenclature of organic chemistry: In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC).  It is published in the "Nomenclature of Organic Chemistry" (informally called the Blue Book).  Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created.  There is also an IUPAC nomenclature of inorganic chemistry.

Organic Reactions: Organic Reactions is a secondary reference which synthesizes the organic chemistry literature around particular chemical transformations.  Each chapter of "Organic Reactions" is devoted to a particular organic chemical reaction, and chapters provide exhaustive coverage of literature work in the form of a tabular survey of known reactions.  Mechanistic and experimental details, including the scope and limitations of each transformation, are also included.

Supporting paragraphs: Homovanillic acid Dopamine
Answer: oxidative enzymes