Biochemistry Classification of Proteins

Active Proteins

Have the ability to bind with other molecules (e.g Hemoglobin)

Passive Proteins

Do not have the abiity to bind with other molecules (e.g Collagen)

Simple Proteins

Basically composed of amino acids. Further classified based on solubility on solvents and heat coagulability

Simple Proteins examples

• Albumin

• Globulin

• Prolamins

• Glutelins

• Histones

• Protamines

• Albuminoids

Albumin

• Readily soluble in water, dilute acids, and alkalies and coagulated by heat

• Seed Proteins contain albumin in lesser quantities

• Precipitates on high salt concentration (“salting out”)

• Deficient in Glycine

Globulin

• insoluble or sparingly soluble in water but their solubility is greatly increased by the addition of neutral salts such as sodium chloride

• These proteins are coagulated by heat

• Deficient in methionine

Prolamins

• insoluble in water but soluble in 70-80% aqueous alcohol.

• Hydrolysis yields much proline and amine nitrogren

• Deficient in lysine

Glutelins

• Insoluble in water and absolute alcohol but soluble in dilute alkalies and acids

• Plant Proteins

Histones

• small and stable basic proteins and contain fairly large amounts of basic amino acids, histidine.

• Soluble in water but insoluble in ammonium hydroxide

• Not readily coagulated by heat

• Present in Globin of haemoglobin and nucleoproteins

Protamines

• The simplest of the proteins

• Soluble in water but not coagulated by heat

• Large quantities of arginine cause them to basic in nature

• Found in association with nucleic acid in the sperm cells of certain fish

• Tyrosine and tryptophan are usually absent in protamines

Albuminoids

• Great stability and insolubility in water and salt solutions.

• Essentially similar to albumin and globulins

• Highly resistant to proteolytic enzymes

• Fibrous in nature and form most of the supporting structures of animales

• Appear as chief constituent of exoskeleton structures such as hair, horn, and nails

Conjugated proteins

Simple proteins linked to non-protein groups (prosthetic groups)

Upon Hydrolysis form amino acids and their non protein groups

Examples of Conjugated Proteins

• Chromoproteins

• Pigments (Hemoglobin)

• Mucoprotein

• Carbohydrate (mucin and globulin)

• Glycoprotein

• Carbohydrate

• Nucleoprotein

• Nucleic Acid (virus)

• Lipoprotein

• Phospholipids (Lecithoprotein)

• Flavoprotein

• Flavin nucleotide (a.a Oxidase)

• Metalloprotein

• Metal (ferritin)

• Phosphoprotein

• Phosphate (casein)

Derived Proteins

Proteins derived by partial/complete hydrolysis from simple or conjugated proteins from acids, alkalies, or enzymes. They include two types of derivative, primary-derived proteins, and secondary-derived proteins

Primary derivative proteins

• No change in molecular wieght after heating

• Formed from processes causing only slight changes in the protein molecule and its properties.

• There is little or no hydrolytic cleavage of peptide bonds

• Protean, Metaproteins, Coagulated Proteins

Secondary Derived Proteins

• Formed from progressive hydrolytic cleavage of the peptide bonds of protein molecule

• Roughly grouped into proteoses, peptones, and peptides according to average molecular weight

Proteoses

Are hydrolytic products of proteins, which are soluble in water and are not coagulated by heat

Peptones

Are hydrolytic products with simpler structures than proteoses

Soluble in water and not coagulated by heat

Peptides

Composed of few amino acids

Water soluble and not coagulated by heat

Hydrolytic decomposition of the natural protein molecule into amino acids (Stages)

Protein > Protean > Metaprotein > Proteoses > Peptones > Peptides > Amino Acids

Classification of Proteins according to shape

Fibrous and Globular

Fibrous

• Structural protein of animals and include the proteins of hair skin nails and connective tissues

• Arranged in parallel along a single axis

• Insoluble in water and generally resistant to denaturation

Examples are collagen, keratin, myosin and fibrin

Globular

• Arranged in tight, compact spherical shape

• Soluble in water

• They are proteins of milk, meat, and eggs

• More sensitive to denaturation

Classification of Proteins according to Biological Importance

• Structural protein

• Contractile Proteins

• Enzymes

• Hormones

• Transport Proteins

• Protective/Defensive Proteins

• Storage proteins

• Toxins

Structural Proteins

Keratin - Primary constituent of skin, hair, and fingernails

Collagen - makes up tendous and developing bones

Elastin - elastic connective tissue

Contractile proteins

Structural components of muslces, for control and relaxation

• Actin

• Myosin

Enzymes

• Biggest class of proteins

• metabolic proteins

• biological catalyst

• e.g Trypsin and Amylase

Hormones

• Needed for the regulation of metabolism

• Not all of these are protein in nature

• e.g Insulin and GH

Transport Proteins

• Hemoglobin

• Iron-binding globulin

• Serum albumin

• Myoglobulin

Protective/Defensive Proteins

• Antibodies

• Fibrinogen

• Thrombin

Antibodies

• prevent invading viruses and bacteria

• forms complexes with foreign particles

Storage Proteins

• Casein

• Ovalbumin

• Zein

• Gliadin

Toxins

• Snake venom

• Ricin

• Clostridium Botolinum Toxin