Proteins that can be hydrolyzed by acid or enzyme to obtain only amino acids are called simple proteins. Simple proteins are divided into seven categories based on solubility.
1. Albumin: Proteins that dissolve easily in water and form a cloudy solution are called albumin. It dissolves in water and a weak salt solution. It coagulates on application of heat. It is widely available in nature. Their molecular weight is 45000-65000 daltons. This protein is found in egg whites, plasma, milk, leaves and seeds. For example, ovalbumin (egg white, 10-12%), beta-amylase (barley, barley), lactoalbumin (milk), serum-albumin (blood and lymph 4-5%), legumin (pea), leucosin (wheat, algae), ligumelin (bean), myo-albumin (muscle), myosin (muscle) etc.
2. Globulin: Globulin is insoluble in water but soluble in weak salt solutions. It coagulates in heat. It is stored as stored food in seeds. However, this protein is also found in animal bodies. Their molecular weight is 3500 daltons. It is present in egg yolk, plasma and semen. Eg- phosvitin (yolk), ovoglobin (egg yolk), tuberin (round potato), lactoglobin (milk), ovoglobin (seed), alphaglobin (blood), serumglobin (blood), myosinogen (muscle), pseudoglobulin (chick/whey). , glycine (soybean), pomelin (orange), erachin (peanut), legumin (pea), edestin (cotton/shaan), crystallin (eye lens) etc.
3. Glutelin: Glutelin is insoluble in water, but soluble in mild acids and alkalis. It does not coagulate in heat. It is present in plant grains. Animals do not contain glutelin. Eg – Glutenin (Wheat/Bhutra), Origenin (Rice) etc.
4. Protamine: Protamine is the smallest protein. It is soluble in water, weak acids and ammonium hydroxide. It does not coagulate in heat. Their molecular weight is 5,000 daltons. This protein is found in the nucleus of some fish sperm. For example, clupine (herring), arginine (rice), salmin (salmon), cyprinine (carp), stearine (sturgeon) etc.
5. Prolamine: The protein which hydrolyzes to produce large amount of proline and ammonia is called prolamine. It is insoluble in water. But 70-80% soluble in ethyl alcohol. They do not coagulate in heat. It is found only in the seeds of plants. Animals do not contain prolamin. Eg – gliadin (rice/rye/wheat), zein (bhutra), hordin (barley/barley) etc.
6. Histone: Histone protein is composed of several basic amino acids. It is soluble in water, but insoluble in ammonium hydroxide. They do not coagulate in heat. It is located in the nucleus or chromosomes. Chromosomes contain histone proteins H1, H2, H3, H4 etc. Histones play an important role in gene expression. For example, arginine, lysine, nucleohistone, globin etc.
7. Scleroprotein: This protein is insoluble in water, salt, acid and alkaline solutions. It is called ‘animal skeletal protein’. This protein is not present in the plant body. Lives only in animal bodies. It has no action on enzymes. It is found in animal bones, hair, nails, horns, skin, hoofs etc. Eg- keratin (skin, nails, hair), collagen (skin), tendon (bone), elastin (ligament), fibroin (silk) etc.