d-serine

D-Serine ((R)-Serine) is an endogenous amino acid,is a potent co-agonist at the NMDA glutamate receptor.

DL-Serine is a non-essential amino acid and a natural ligand and allosteric activator of pyruvate kinase M2.

D-(+)-Xylose (Wood sugar) is an aldopentose - a monosaccharide containing five carbon atoms and an aldehyde functional group. It has chemical formula C5H10O5 and is 40% as sweet as sucrose. Xylose is also found in mucopolysaccharides of connective tissue and sometimes in the urine. Xylose is the first sugar added to serine or threonine residues during proteoglycan type O-glycosylation. Therefore xylose is involved in the biosythetic pathways of most anionic polysaccharides such as heparan sulphate and chondroitin sulphate. In medicine, xylose is used to test for malabsorption by administering a xylose solution to the patient after fasting. If xylose is detected in the blood and/or urine within the next few hours, it has been absorbed by the intestines. Xylose is said to be one of eight sugars which are essential for human nutrition, the others being galactose, glucose, mannose, N-acetylglucosamine, N-acetylgalactosamine, fucose, and sialic acid. . Xylose in the urine is a biomarker for the consumption of apples and other fruits.

D-Isoleucine ((2R,3R)-2-Amino-3-methylpentanoic acid) is a selective activator of Asc-1 antiporter, which enhances long-term potentiation at the hippocampal CA1-CA3 via release of endogenous D-serine.

Pyridoxal 5'-phosphate hydrate (PLP)(1:x), the active form of vitamin B6, is a cofactor for many different enzymes involved in transamination reactions, including mitochondrial cysteine desulfurase, cystathionine γ-synthase, various aminotransferases, and a d-serine dehydratase.