Legumin is family of globular

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s obtained from

beans A bean is the seed of some plants in the legume family (Fabaceae) used as a vegetable for human consumption or animal feed. The seeds are often preserved through drying (a ''pulse''), but fresh beans are also sold. Dried beans are tradition ...

peas Pea (''pisum'' in Latin) is a pulse or fodder crop, but the word often refers to the seed or sometimes the pod of this flowering plant species. Peas are eaten as a vegetable. Carl Linnaeus gave the species the scientific name ''Pisum sativum ...

lentils The lentil (''Vicia lens'' or ''Lens culinaris'') is an annual plant, annual legume grown for its Lens (geometry), lens-shaped edible seeds or ''pulses'', also called ''lentils''. It is about tall, and the seeds grow in Legume, pods, usually w ...

, vetches,

hemp Hemp, or industrial hemp, is a plant in the botanical class of ''Cannabis sativa'' cultivars grown specifically for industrial and consumable use. It can be used to make a wide range of products. Along with bamboo, hemp is among the fastest ...

and other leguminous seeds. Garden peas are a common nutritional source for humans that contains legumin. Legumin is similar to the

casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins (CSN1S1, αS1, aS2, CSN2, β, K-casein, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of ...

of mammalian milk and was called "vegetable casein" since it was considered analogous to the mammalian protein. The primary function of the legumin protein in seeds is storage. Legumin proteins are one of the main storage proteins of

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit. T ...

and

gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...

s. Legumin is an insoluble hexameric conjugated protein with a high concentration of carbon and oxygen.

Properties

Structure

Legumin is a conjugated protein with six subunits. The individual subunits have a hydrophilic α chain that is initially linked to the smaller hydrophobic β chain with a peptide bond. Both the α and β chains are encoded by the same gene. Each of the six subunits has a mass of ~50-60 kDa. During

translation Translation is the communication of the semantics, meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The English la ...

of the α and β chains, the polypeptide is inserted into the

endoplasmic reticulum The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...

(ER) where the

signal peptide A signal peptide (sometimes referred to as signal sequence, targeting signal, localization signal, localization sequence, transit peptide, leader sequence or leader peptide) is a short peptide (usually 16–30 amino acids long) present at the ...

that initiated the cell to translocate the chains is cleaved. A disulfide bridge is formed between the α and β chains to form prolegumin, a

protein precursor A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein (or peptide) that can be turned into an active form by post-translational modification, such as breaking off a piece of the molecule or adding on another molecule ...

. Three of these subunits come together to form a trimer in the ER. The trimer of prolegumins can be transported to the vacuole for further

post-translational modification In molecular biology, post-translational modification (PTM) is the covalent process of changing proteins following protein biosynthesis. PTMs may involve enzymes or occur spontaneously. Proteins are created by ribosomes, which translation (biolog ...

. In the vacuole, the peptide bond formed between the α and β chains is cleaved now that the disulfide bridge holds the two chains together. The cleavage of the α and β chains within the trimers signals protein maturation where two trimers to come together and form the final hexameric legumin protein.

Composition

Although legumin is similar to casein of mammalian milk but it contains less carbon and more nitrogen than true casein. Karl Heinrich Ritthausen found legumin from peas, vetches, lentils, and field beans to contain the elements in the following proportions: carbon, 51.48%; hydrogen, 7.02%; nitrogen, 16.77%; and oxygen, 24.32%. When treated with

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

, legumin breaks down to

leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-Car ...

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a conditionally essential amino acid with a polar side group. The word "tyrosine" is ...

, and glutamic and

aspartic acid Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids, i.e., the building blocks of protei ...

s. Legumin proteins are relevant because their composition as a storage protein means they are a highly biologically active source of protein. Legumes like beans, lupins, and peas have great nutritional value for humans. They provide an inexpensive but effective low fat protein source. Although peas are commonly consumed as a source leguminous protein, lupins and soybeans provide a much higher protein content. Legumes are also a rich source of essential amino acids.

Solubility

Legumin proteins are insoluble in water because of their hydrophobic units. Legumins are soluble in very weak

acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...

s and alkalies. This protein is not coagulated by heat. Due to their important storage function legumin proteins and another important storage protein vicilin have been found be to the most abundant water and alkali soluble proteins within cottonseed.

References

{{reflist Seed storage proteins

Properties

Structure

Composition

Solubility

See also

References