Protein & Types of protein with examples

                         PROTEIN

INTRODUCTION

Proteins are firstly introduced by the Dutch chemist Gerardus Johannes Mulder and named gave by the Swedish chemist Jöns Jacob Berzelius in 1838.Mulder carried out elemental analysis of common protein formulaC₄₀₀H₆₂₀N₁₀₀O₁₂₀P₁S₁.

Protein is derived from the Greek word  

Proteios + in = meaning "primary"/ "in the lead", or "standing in front".

German Nutritional scientists Carl von Voit believed in protein which is most important nutrient for maintaining the structure of the body, because they believed in "flesh makes flesh.

Definition- Proteins are very large, complex molecules which are composed with carbon, hydrogen, oxygen, nitrogen, and sulphur.

That play many roles in the body like structure, function, and regulation of the body’s tissues and organs.

Classification based on composition and solubility -

 Proteins are divided into 3 types:

 

1. Simple Proteins or Holoproteins

These are globular type except fibrous proteins which are fibrous in nature. This group involves in containing only amino acids, as structural components.

On decomposition with acids, they release the amino acids.

 These are further classified mainly on their solubility basis as follows:

1. Protaminase and histones
2. Albumins
3. Globulins
4. Glutelins
5. Prolamines
6. Scleroproteins or Albuminoids

 

2. Conjugated or Complex Proteins or Heteroproteins

These are also of globular type except pigment in chicken feathers so it’s fibrous in nature. These proteins are linked with separable non-protein portion called prosthetic group (metal or a compound).

On decomposition with acids, they gave the constituent of amino acids as well as the prosthetic group. 

Classification is based on nature of prosthetic group present-

1. Metalloproteins
2. Chromo- proteins
3. Glycoproteins
4. Phosphoproteins
5. Lipoproteins
6. Nucleoproteins

3. Derived Proteins

These are created from other proteins through chemical or physical proteins means heat, enzymes or chemical reagents. This group also includes the artificially-produced polypeptides.

I. Primary derived proteins

In this derived proteins size of protein molecule is not exchange.

1. Proteans: Its insoluble in water first product formed by action of acids, enzymes or water on proteins. e.g., edestan derived from edestin and myosan derived from myosin.

2. Meta-proteins or Infra-proteins: These are insoluble in water but soluble in dilute acids or alkaline solution and formed by action of acid or alkali on proteins at about 30–60°C. e.g., acid and alkali meta-proteins.
3. Coagulated Proteins: These are also insoluble in water and formed by the action of heat or alcohol on proteins. e.g., coagulated egg white.

II. Secondary derived proteins

These are derivatives of proteins in which the hydrolysis has certainly occurred. The molecules are, as a rule, smaller than the original proteins.

1. Proteoses: These are soluble in water, coagulated by heat and produced when hydrolysis the level of metaproteins,

 Primary proteoses are salted out by half saturation with Diazanium sulphate ((NH4)2.SO4) and precipitated by Nitric acid (HNO3) and picric acid.
 

Secondary proteoses are salted out only by complete saturation with Diazanium sulphate ((NH4)2.SO4) but are not precipitated by Nitric acid (HNO3) or picric acid.

 E.g- albumose from albumin, globulose from globulin.

2. Peptones: It is soluble in water, but non- coagulated by heat and produced by the action of dilute acids or enzymes when hydrolysis proceeds proteoses neither salted out by Diazanium sulphate ((NH4)2SO4) not precipitated by HNO3 or picric acid.

3. Polypeptides: These are the combinations of two or more amino acid units. In also called as proteins are essentially long chain polypeptides.

4. Peptides- These Peptides are short polypeptides but the difference between polypeptides and peptides is random and there is no clear-cut elected between the lengths of peptides and polypeptides.

Classification of proteins based on solubility –
Based on solubility, the simple proteins may be sub-classified into various types of proteins like – Albumin, Prolamins, Glutelins, Histones, Protamines, Globulins, Scleroproteins or Albuminoids
 etc.

Albumins-

 Albumins are willingly soluble in water, dilute in acids and alkalis but coagulated by heat.

• Eg- Ovalbumin (storage protein as egg white) It is a serpin.
• Lactalbumin, or whey protein, is a protein fraction of milk.

Globulins-

Globulins are in sparingly soluble in water, but highly solubility are enhanced by addition of neutral salts such as -sodium chloride. 

Its play an important role in liver function, blood clotting, and fighting infection. Eg-   Haemoglobin (Hb) Myoglobin (Mb) Neuroglobin

Prolamins- Prolamins are insoluble in water but soluble in 70-80% aqueous alcohol. After hydrolysis, they give yield in high amounts of proline and amide nitrogen, in comparison to prolamin. 

Eg- Gliadin (Found in wheat), Hordein(Found in barley), Zein (Found in corn), Secalin (Found in rye), Kafirin (Found in sorghum), Avenin (Found in oats), Orzein (Found in rice)

Glutelins – Glutelins are insoluble in water and absolute alcohol but soluble in dilute alkalies and acids. They are usually found in plant proteins Eg. Glutenin (wheat).

Histones – Histones are small, highly basic proteins with water soluble ability it’s contain high amounts of basic amino acid Eg- Histidine, lysine, andarginine.

Albuminoids (scleroproteins) - They are highly stable and insoluble in water and salt solutions. They are also called as an albuminoids and they are similar to albumin and globulins. Eg- Vitamin D-binding protein (GC), Alpha-fetoprotein (AFP), Afamin (AFM), and Albumin (ALB)