MOLECULE

D-Galactose

D-galactose, also known as galactopyranose, is an aldohexose is a C4-epimer of glucose. It is as sweet as glucose and only 65% as sweet as sucrose. When D-galactose condenses with glucose, lactose if formed. In humans and other species, galactose is metabolized to glucose largely by the Leloir pathway. D-galactose is converted to UDP-glucose and glucose-1-phosphate by three enzymes (PMID: 1292318):  1) Galactokinase (GALK; KEGG enzyme E.C. 2.7.1.6) phosphorylates D-galactose to D-galactose-1-phosphate; 2) Then D-galactose-1-phosphate uridyltransferase (GALT; KEGG enzyme E.C. 2.7.7.12) transfers a UMP from UDP-glucose to D-galactose-1-phosphate to form UDP-galactose and glucose-1-phosphate. Glucose-1-phosphate will then enter the glycolytic pathway for energy production. 3) UDP-galactose epimerase (GALE) then interconverts UDP-galactose to UDP-glucose. Lactose in mammalian milk is the main source of D-galactose. Galactose in the urine is a biomarker for the consumption of milk. Galactose can also be found in some fruits and vegetables such as in banana, orange, papaya, bell pepper, avocado and sugar beets ( http://www.thegoodscentscompany.com/data/rw1233801.html#tooccur). It is also found in fig leaves, sesame, carob bean, caraway seeds and beet, cocoa, chive, potato, and cannabis plants (PMID: 6991645). In addition to D-Galactose providing energy for the body, it is also a necessary substrate for the biosynthesis of many macromolecules such as cerebrosides, gangliosides, and mucoproteins. Galactose is a component of the antigens of the ABO blood group (PMID: 15373665). Metabolic pathways for D-galactose are important not only for the provision of these pathways but also for the prevention of D-galactose accumulation. There are diseases resulting from the deficiencies of the three enzymes of the Leloir pathway. Classic galactosemia, or the accumulation of D-galactose in the blood, is the rare inborn error of D-galactose metabolism, caused by the deficiency of the second enzyme GALT, (from mutations in the GALT gene; PMID: 10408771). As galactose accumulation is associated with health problems (PMID: 26001656), particularly involving the liver (PMID: 29502917), the discovery of alternative metabolic pathways to the Leloir in fungi and bacteria (PMID:15256214) could lead to discovery of analogous genes in humans. D-galactose was also be protective against pancreatitis (PMID: 2989374) and streptozotocin-induced model of Alzheimer’s disease in rats (PMID: 29501615). D-Galactose is expected to be in Cannabis as all living plants are known to produce and metabolize it.