Page last updated: 2024-10-24

S-adenosylmethionine cycle

Definition

Target type: biologicalprocess

A cyclic series of interconversions involving S-adenosylmethionine, S-adenosyl-L-homocysteine, L-cysteine, and L-methionine. Couples utilization of the methyl group of SAM with recycling of the homocysteinyl group and regeneration of methionine. [GOC:mah, MetaCyc:PWY-5041]

The S-adenosylmethionine (SAM) cycle is a fundamental metabolic pathway crucial for numerous cellular processes. It begins with the synthesis of SAM from methionine and ATP, catalyzed by the enzyme methionine adenosyltransferase (MAT). SAM serves as a universal methyl donor in a wide range of methylation reactions, including DNA, RNA, proteins, and lipids. These methylation events regulate gene expression, protein function, and cellular signaling. After donating its methyl group, SAM is converted to S-adenosylhomocysteine (SAH), a potent inhibitor of most methyltransferases. SAH is then hydrolyzed to homocysteine and adenosine by SAH hydrolase. Homocysteine can be remethylated back to methionine by tetrahydrofolate reductase (THF reductase) or incorporated into cysteine via the transsulfuration pathway. The cycle is tightly regulated to ensure optimal SAM levels and proper cellular function. Defects in the SAM cycle can lead to various diseases, including homocystinuria, neurodevelopmental disorders, and cancer.'
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Proteins (1)

ProteinDefinitionTaxonomy
AdenosylhomocysteinaseAn adenosylhomocysteinase that is encoded in the genome of human. [PRO:DNx, UniProtKB:P23526]Homo sapiens (human)

Compounds (17)

CompoundDefinitionClassesRoles
3-deazaadenosine3-deazaadenosine: RN given refers to parent cpd.
ribavirinRebetron: Rebetron is tradename1-ribosyltriazole;
aromatic amide;
monocarboxylic acid amide;
primary carboxamide
anticoronaviral agent;
antiinfective agent;
antimetabolite;
antiviral agent;
EC 2.7.7.49 (RNA-directed DNA polymerase) inhibitor
adenosinequinquefolan B: isolated from roots of Panax quinquefolium L.; RN not in Chemline 10/87; RN from Toxlitadenosines;
purines D-ribonucleoside
analgesic;
anti-arrhythmia drug;
fundamental metabolite;
human metabolite;
vasodilator agent
aristeromycinaristeromycin: RN given refers to (1R-(1alpha,2alpha,3beta,5alpha)-isomer
illimaquinoneillimaquinone: structure given in first source; isolated from the Red Sea sponge Smenospongia; inhibits the RNase H. activity of HIV-1 reverse transcriptasemonohydroxy-1,4-benzoquinones;
prenylquinone
metabolite
3-deazaaristeromycin3-deazaaristeromycin: antagonist of S-adenosylhomocysteinase
neplanocin aneplanocin A: neplanocins are antitumor antibiotics & carbocyclic analogs of purine nucleosides from Ampullarilla regularis A11079; see also neplanocin B, neplanocin C, neplanocin D & neplanocin F; structure in first source; a potent inhibitor of S-adenosylhomocysteine hydrolase
3-deazaneplanocin3-deazaneplanocin: S-adenosylhomocysteine hydrolase antagonist
9-(2',3'-dihydroxycyclopentan-1'-yl)adenine9-(2',3'-dihydroxycyclopentan-1'-yl)adenine: inhibitor of S-adenosylhomocysteine hydrolase; structure given in first source
adenosine-5'-carboxylic acidpurine nucleoside
5'-n-methylcarboxamideadenosine5'-N-methylcarboxamideadenosine: RN given refers to (beta-D)-isomer
5'-noraristeromycin5'-noraristeromycin: structure given in first source
adenosine-5'-carboxaldehyde5'-dehydroadenosine : A member of the class of adenosines that is 5'-dehydro derivative of adenosine.

adenosine-5'-carboxaldehyde: potent inhibitor of S-adenosyl-L-homocysteine hydrolase; structure given in first source
adenosines
9-(2',3'-dihydroxycyclopent-4'-enyl)adenine
5'-amino-5'-deoxyadenosine
guanosineribonucleoside : Any nucleoside where the sugar component is D-ribose.guanosines;
purines D-ribonucleoside
fundamental metabolite
inosineinosines;
purines D-ribonucleoside
Escherichia coli metabolite;
human metabolite;
mouse metabolite;
Saccharomyces cerevisiae metabolite