Globular protein

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3-dimensional structure of hemoglobin, a globular protein.

Globular proteins are a common type of protein.

They are one of three types of protein. The others are fibrous and membrane proteins.

Their structure is a result of protein folding. They are made of polypeptide chains folded into a compact sphere shape.

They are soluble in water because of the hydrophilic ('water-loving') side chains that project from the outside of the molecules. They play an important role in metabolic reactions.

Unlike proteins which only have a structural function, globular proteins can act as:

  • Enzymes, by catalyzing organic reactions taking place in the organism in mild conditions and with a great specificity. Different esterases fulfill this role.
  • Messengers, by transmitting messages to regulate biological processes. This function is done by hormones, i.e. insulin etc.
  • Transporters of other molecules through membranes
  • Stocks of amino acids.
  • Regulation of other molecules is also done by globular proteins rather than fibrous proteins.
  • Structural proteins, e.g., actin and tubulin, which are globular and soluble as monomers, but polymerize to form long, stiff fibers.

Globular proteins include myoglobin and hemoglobin.