Language
Country/Area
No result found
Deciphering the chemical structure of galactose: Why is it inextricably linked to glucose?
Galactose, sometimes referred to as Gal, is a monosaccharide with a sweetness comparable to that of glucose, about 65% of the sweetness of sucrose. It is an aldose and the C-4 epimer of glucose. When a galactose molecule combines with a glucose molecule, lactose is formed. A polymeric form of galactose, called galactan, is found in hemicellulose, which forms a class of naturally occurring polymeric carbohydrates called galactans. D-galactose is also known as "brain sugar" because it is a component of glycoproteins (oligosaccharide-protein compounds) in neural tissue.
"In the world of biochemistry, galactose and glucose are like close partners, relying on each other and forming many cornerstones of life."
Structure of galactose
Galactose can exist in open chain and ring forms. The open-chain form has a carbonyl group at the end of the chain. The cyclic form has four isomers, two of which are pyranose (six-membered rings) and the other two are furanose (five-membered rings). In the cyclic form, because a new stereocenter is generated at the open-chain carbonyl position when converting from the open-chain form to the cyclic form, two isomers are produced, namely α-form and β-form.
According to infrared spectroscopy, galactose shows a broad and strong stretching from about 2500 cm−1 to 3700 cm−1. At the same time, the characteristics of galactose can also be observed in the proton nuclear magnetic resonance (NMR) spectrum at 4.7ppm, 4.15ppm and multiple other chemical shifts.
The relationship between lactose and galactose
Lactose is a disaccharide formed by the dehydration reaction of galactose and glucose. The hydrolysis of lactose is catalyzed by lactase and β-galactosidase, which are enzymes from the lactose operon of Escherichia coli. In nature, lactose is mainly found in milk and dairy products. Therefore, many foods that are made with dairy products contain lactose.
"Galactose metabolism is critical because it not only supports lactose production, but also plays a variety of physiological roles."
During the lactation process, humans need to consume galactose and glucose in a 1:1 ratio so that the mammary glands can synthesize and secrete lactose. Studies have shown that when women consume a galactose-rich diet, a significant portion of the lactose they produce comes from glucose and galactose in plasma.
Galactose Metabolism
The human body cannot directly convert galactose into energy; it must first go through a series of metabolic pathways, especially the famous Leloir pathway. This pathway involves several major enzymes, including galactokinase (GALK), galactose-1-phosphate uridyltransferase (GALT), and uridine-galactose-4'-epimerase (GALE). These enzymes work together to convert β-D-galactose into UDP-glucose. Each step of this process is essential. If any one of the enzymes is missing, it will lead to galactose intolerance, causing great distress to the patient.
Sources of Galactose
Galactose is found in dairy products, avocados, sugar beets and many gums and mucilages. In addition, it can also be synthesized in vivo as part of glycolipids and glycoproteins in various tissues. Its synthesis process may also involve certain bioconversion processes, such as the production of third-generation ethanol extracted from seaweed.
Clinical significanceAnimal experiments with long-term exposure to D-galactose have shown that this may accelerate the aging process. In addition, studies have shown that high doses of D-galactose can affect the fertility of organisms. Some preliminary studies even suggested a possible link between galactose and ovarian cancer, but a broad examination of the results showed no clear association. Recent studies have focused on the potential positive effects of galactose in kidney diseases such as focal tubular sclerosis.
Historical BackgroundAs early as 1855, E. O. Erdmann noticed that the hydrolysis of lactose produced substances other than glucose. Galactose was first isolated and studied by Louis Pasteur in 1856, when he called it "lactose". Subsequently, in 1860, Portello renamed it "galactose". In 1894, Emil Fischer and Robert Morel determined the structure of galactose.
Galactose is demonstrating its importance in biochemistry and clinical medicine, and future research may reveal more about this sugar. Have you ever thought about how this common material, sugar, can profoundly affect human health and disease?
