S-Adenosylhomocysteine

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S-Adenosylhomocysteine
2D structure for S-Adenosylhomocysteine
Chemical Name	(2S)-2-amino-4-[[(2S,3S,4R,5R)-5-(6-aminopurin-9-yl)-3,4-dihydroxy-oxolan-2-yl]methylsulfanyl]butanoic acid
Chemical Formula	C₁₄H₂₀N₆O₅S
CAS Number	979-92-0
Chemical Information	HMDB00939
Biochemical Taxonomy	Nucleosides
Functional Taxonomy	Not Available
Nutritional Taxonomy	Not Available
Metabolic Pathways	Glycerophospholipid Metabolism Glycine, Serine and Threonine Metabolism Lysine Degradation Methionine Metabolism Nicotinate and Nicotinamide Metabolism Ubiquinone Biosynthesis
Biofluid Location	Blood Cerebrospinal Fluid (CSF)
Tissue Location	Myelin Neurons Placenta Lymphoblast
Normal Biofluid Concentrations	Blood: 0.46 +/- 0.02 uM Cerebrospinal Fluid (CSF): 0.01 (0.009-0.014) uM
Normal Tissue Concentrations	Not Available
Diseases / Conditions Related to Nutrition	Patients with Parkinson's Disease Patients with neurodegenerative diseases
Other (Monogenic Disorders)	Not Available
Abnormal Biofluid Concentrations	Blood (Patients with Parkinson's Disease): 0.49 +/- 0.05 uM Blood (Patients with neurodegenerative diseases): 0.016 (0.009-0.025) umol/L
Abnormal Tissue Concentrations	Not Available
Physiological Processes	Not Available

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Introduction

guidelines
S-Adenosylhomocysteine (AdoHcy) is the immediate precursor of all of the homocysteine produced in the body. The reaction is catalyzed by S-adenosylhomocysteine hydrolase and is reversible with the equilibrium favoring formation of AdoHcy. In vivo, the reaction is driven in the direction of homocysteine formation by the action of the enzyme adenosine deaminase, which converts the second product of the S-adenosylhomocysteine hydrolase reaction, adenosine, to inosine. Except for methyl transfer from betaine and from methylcobalamin in the methionine synthase reaction, AdoHcy is the product of all methylation reactions that involve S-adenosylmethionine (AdoMet) as the methyl donor. Methylation is significant in epigenetic regulation of protein expression via DNA and histone methylation. The inhibition of these AdoMet-mediated processes by AdoHcy is a proven mechanism for metabolic alteration. Because the conversion of AdoHcy to homocysteine is reversible, with the equilibrium favoring the formation of AdoHcy, increases in plasma homocysteine are accompanied by an elevation of AdoHcy in most cases. Disturbances in the transmethylation pathway indicated by abnormal S-adenosylmethionine, S-adenosylhomocysteine or their ratio have been reported in many neurodegenerative diseases, such as dementia, depression or Parkinson's disease. (PMID: 18065573, 17892439)