Two metabolic pathways exist for the biosynthesis of isopentenyl pyrophosphate and dimethylallyl pyrophosphate: The mevalonate pathway, predominantly used by plants and in a few insect species. The non-mevalonate pathway or methyl D-erythritol 4-phosphate (MEP) pathway, which occurs in plant chloroplasts
Acetylcholine is synthesized from acetyl coenzyme A and choline by the enzyme choline acetyltransferase. In addition to its synthesis in the liver, choline employed in acetylcholine production is derived from dietary sources.
Glutamine is a common precursor for the biosynthesis of both glutamate and GABA. Glutamine can be transported in and out of neurons and astrocytes utilizing different glutamine carriers. The neurotransmitter glutamate can be synthesized from glutamine by the action of
Neurotensin is a 13 amino acid regulatory peptide found mainly in gut and brain. Intestinal neurotensin is produced by a discrete population of endocrine cells (N cells) scattered throughout the jejuno-ileal mucosa.
Either monoamine oxidase A (MAO) or catechol-O-methyltransferase (COMT) can catalyze the first step in catecholamine catabolism. The potentially toxic aldehyde intermediate generated in the MAO reaction (3,4-dihydroxyphenylacetaldehyde for dopamine, 3,4-dihydroxyphenylglycolaldehyde for norepinephrine) is either rapidly reduced to an alcohol (by
Dopamine-β-hydroxylase is located inside amine storage vesicles of norepinephrine neurons. Dopamine is actively transported from the cytoplasm into the vesicles. As the enzyme is a copper containing protein, its activity can be inhibited by copper chelating agents, such as diethyldithiocarbamate
Glucose metabolism is regulated by the opposing actions of insulin and glucagon. Insulin is released from pancreatic ß cells in response to high blood glucose levels and regulates glucose metabolism through its actions on muscle, liver, and adipose tissue.