The glucans are perhaps the most abundant carbohydrates in the biosphere. Most make up the cell wall of bacteria, plants, yeasts, and other living organisms. Some make up the reserve substances of vertebrates .
All glucans are made up of one type of repeating monosaccharide: glucose. However, these can be found in a great variety of forms and with a great variety of functions.
The name glucan has its main origin from the Greek word ” glykys “, which means “sweet.” Some textbooks refer to glucans as non-cellulosic polymers made up of glucose molecules linked by β 1-3 bonds (when saying “non-cellulosic”, those that are part of the cell wall of plants are excluded from this group) .
However, all polysaccharides composed of glucose, including those that make up the cell wall of plants, can be classified as glucans.
Many glucans were among the first compounds to be isolated from different life forms to study the physiological effects they had on vertebrates, especially on the immune system of mammals.
Glycans have a relatively simple composition, despite the great diversity and complexity of structures that can be found in nature. All are large glucose polymers linked by glycosidic bonds, the most frequent bonds being α (1-3), β (1-3) and β (1-6).
These sugars, like all saccharides that have glucose as their base, are fundamentally composed of three types of atoms: carbon (C), hydrogen (H) and oxygen (O), which form cyclic structures that can be joined together. yes forming a chain.
Most of the glucans consist of straight chains, but those that present branches are joined to these through glucosidic bonds of type α (1-4) or α (1-4) in combination with α (1-6) bonds.
It is important to mention that most of the glucans with “α” bonds are used by living beings as an energy supply, metabolically speaking.
The glucans with the highest proportion of “β” bonds are more structural carbohydrates. These have a more rigid structure and are more difficult to break by mechanical or enzymatic action, so they do not always serve as a source of energy and carbon.
Types of glucans
These macromolecules vary according to the anomeric configuration of the glucose units that compose them; the position, type and number of branches that join them. All variants have been classified into three types of glucans:
– β-glucans (cellulose, lichenine, cymosan or zymosan, etc.)
– α, β-glucans
– α-glucans (glycogen, starch, dextran, etc.)
Α, β-Glucans are also known as “mixed glucans”, since they combine different types of glycosidic bonds. They have the most complex structures within carbohydrates and generally have structures that are difficult to separate into smaller carbohydrate chains.
Generally, glucans have high molecular weight compounds, with values that vary between thousands and millions of daltons.
Characteristics of glucans
All glucans have more than 10 glucose molecules linked together and the most common is to find these compounds made up of hundreds or thousands of glucose residues forming a single chain.
Each glucan has special physical and chemical characteristics, which vary depending on its composition and the environment where it is found.
When glucans are purified they do not have any color, aroma or taste, although purification is never as precise as to obtain a single isolated single molecule and they are always quantified and studied “approximately”, since the isolate contains several different molecules.
Glycans can be found as homo- or heteroglycans.
– Homoglycans are composed of only one type of glucose anomer
– Heteroglycans are made up of different anomers of glucose.
It is common for heteroglycans, when dissolved in water, to form colloidal suspensions (they dissolve more easily if they are subjected to heat). In some cases, heating produces ordered structures and / or gels.
The union between the residues that form the main structure of glucans (the polymer) occurs thanks to glucosidic bonds. However, the structure is stabilized through “hydrostatic” interactions and a few hydrogen bonds.