All articles starting with a number or symbol

5-4-3 rule

The 5-4-3 rule, also known as the four repeater rule, limits shared 10 Mbit/s Ethernet collision domains to at most five segments and four repeaters.

5-Aminoimidazole-4-carboxamide

5-Aminoimidazole-4-carboxamide (AICA) is an aminoimidazole derivative whose ribonucleotide, AICAR, is an intermediate in purine biosynthesis, while its riboside, acadesine, is a widely used AMPK activator.

5-Aminolevulinic acid

5-Aminolevulinic acid (5-ALA), also called δ-aminolevulinic acid, is a non-proteinogenic amino acid and common precursor of tetrapyrroles including heme, chlorophyll, and vitamin B12; in cells it converts to fluorescent protoporphyrin IX for tumor imaging.

5-Bromo-2'-deoxyuridine

5-Bromo-2'-deoxyuridine (BrdU), also called broxuridine, is a synthetic thymidine analog that is incorporated into newly synthesized DNA during S phase and is widely used as a marker of cell proliferation and cell fate.

5-carboxymethyl-2-hydroxymuconate isomerase

5-carboxymethyl-2-hydroxymuconate isomerase (CHMI, EC 5.3.3.10) is a trimeric tautomerase-superfamily enzyme of E. coli C's homoprotocatechuate pathway that ketonizes 5-carboxymethyl-2-hydroxymuconate using catalytic Pro-1, distinct from 4-OT by substrate steric specificity.

5-hour Energy

5-hour Energy is an American energy shot launched in 2004 by Manoj Bhargava through Living Essentials LLC, a 1.93 oz sugar-free caffeine and B-vitamin supplement that dominated the energy shot market.

5-HT receptor

5-HT receptor (serotonin receptor): 14 mammalian subtypes in seven families, 13 GPCRs plus the ion-channel 5-HT3 receptor, classified by IUPHAR; targets for antimigraine, anxiolytic, and antipsychotic drugs with subtype-selectivity challenges.

5-HT1A receptor

5-HT1A receptor: inhibitory Gi/o-coupled serotonin GPCR acting as raphe autoreceptor and postsynaptic heteroreceptor; target of buspirone, gepirone, vilazodone, and WAY-100635 in anxiety and depression research.

5-HT2A receptor

5-HT2A receptor, a serotonin GPCR targeted by psychedelics like LSD and psilocybin and by antipsychotics; found in cortical layer V and inside neurons, mediating plasticity and signaling.

5-Hydroxyindoleacetic acid

5-Hydroxyindoleacetic acid (5-HIAA) is the primary metabolite of serotonin, formed by monoamine oxidase A and excreted in urine, where it serves as a tumor marker for serotonin-secreting neuroendocrine tumors.

5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) is an organic compound formed when six-carbon sugars dehydrate under acid catalysis, serving as a bio-based platform chemical for bioplastics, liquid fuels, and pharmaceutical intermediates.

Oct 22, 2026

5-Hydroxymethylfurfural oxidation

5-Hydroxymethylfurfural oxidation is the selective conversion of biomass-derived HMF into 2,5-furandicarboxylic acid (FDCA), a bio-based substitute for terephthalic acid, using thermal, electrocatalytic, photocatalytic, or enzymatic methods.

Oct 22, 2026

5-Hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid

Oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a catalytic conversion that turns biomass-derived HMF into FDCA, a sustainable alternative to terephthalic acid used in polyesters such as PEF, proposed as a PET substitute.

5-Hydroxytryptophan

5-Hydroxytryptophan (5-HTP, oxitriptan), the immediate serotonin precursor formed from tryptophan by tryptophan hydroxylase; sold as a supplement from Griffonia simplicifolia seeds, studied for depression, with contaminant-related EMS history.

Oct 20, 2026

5-lipoxygenase-activating protein

5-lipoxygenase-activating protein (FLAP, ALOX5AP), an 18-kDa integral membrane protein presenting arachidonic acid to 5-lipoxygenase for leukotriene synthesis; MK-886 target and drug candidate for asthma and cardiovascular disease.

5-MeO-DiPT

5-MeO-DiPT (Foxy, Foxy Methoxy) is a synthetic psychedelic tryptamine first described by Shulgin in 1980, active at 6–10 mg for 3–6 hours, a US Schedule I drug with reported agitation, tachycardia, and fatal poisonings.

5-MeO-DMT

5-MeO-DMT, also known as O-methylbufotenine, is a psychedelic tryptamine alkaloid found in the Sonoran Desert toad and in plants; inhaled effects last 5 to 20 minutes, and it is in US Schedule I.

5-MeO-MiPT

5-MeO-MiPT, known online as "Moxy", is a synthetic tryptamine hallucinogen first described in 1985 that emerged as a recreational drug in the 2010s and is proposed for US Schedule I.

5-Methoxytryptamine

5-Methoxytryptamine (5-MT, also called O-methylserotonin or mexamine) is a naturally occurring tryptamine, non-selective serotonergic agonist, and intermediate in an alternate melatonin synthesis pathway.

5-Methylcytosine

5-Methylcytosine (5mC) is cytosine with a methyl group attached, the principal covalent DNA modification in animals, plants, and bacteria that regulates gene expression and is used in cancer screening tests.

5-methylcytosine restriction system component, bacterial

McrBC (formerly RglB), the bacterial 5-methylcytosine restriction system of E. coli K-12, is a two-subunit, GTP-dependent Type IV endonuclease encoded by mcrB and mcrC that cleaves DNA between two RmC sites 40-80 bp apart.

5-Minute Crafts

5-Minute Crafts, also known as Five-Minute Crafts, is a DIY and life-hack video brand on YouTube run by TheSoul Group, with about 80 million subscribers.

5-oxoprolinase deficiency

5-oxoprolinase deficiency is an extremely rare autosomal recessive inborn error of glutathione metabolism, caused by OPLAH variants, that causes persistent 5-oxoprolinuria; its clinical significance is debated.

5-Phosphoribosyl-4-carboxy-5-aminoimidazole

5-Phosphoribosyl-4-carboxy-5-aminoimidazole (CAIR) is a phosphorylated intermediate of de novo purine biosynthesis, the only carbon-carbon bond-forming step, made by PurK and PurE in bacteria or PAICS in vertebrates.

5,10-methenyltetrahydromethanopterin hydrogenase

5,10-methenyltetrahydromethanopterin hydrogenase (Hmd, [Fe]-hydrogenase, EC 1.12.98.2) is a methanogen enzyme reducing methenyl-H4MPT+ with H2 via a mononuclear iron FeGP cofactor, once thought metal-free.

5:00 P.M. (The Pitt season 1)

"5:00 P.M." is season 1, episode 11 of The Pitt (Max, aired March 13, 2025), written by Elyssa Gershman and directed by Quyen Tran; Robby hides a staffing problem while Collins delivers a surrogate's baby, rated 8.7 on IMDb. Distinct from the season 2 ICE episode of the same title.

5:00 P.M. (The Pitt season 2)

"5:00 P.M." is episode 11 of The Pitt season 2 (HBO Max, aired March 19, 2026), written by Valerie Chu, directed by Uta Briesewitz; the ICE episode in which agents bring detainee Pranita into the ER and nurse Jesse is detained.

5.1 surround sound

5.1 surround sound: six-channel audio format with left, center, right, left/right surround plus LFE subwoofer channel; standardized 1987, digitalized by Dolby Digital 1992 and DTS 1993.

5.11 Tactical

5.11 Tactical is an American tactical apparel and gear brand founded in 2003 by Dan Costa from the Royal Robbins climbing-pant line, named for a Yosemite Decimal System climbing grade, headquartered in Irvine, California, serving law enforcement, fire, EMS, and military customers.