Protein Characteristics
Till this point we have discussed about structure and certain related issues of different types of proteins
associated with the muscles. Lets now have a look at biochemical issues related to proteins as the structures
are ultimately formed from biochemicals which through several important biochemical changes end up forming
the structures which we see.

• Proteins are made of amino acids which can be hydrophobic as well as polar
• Polar amino acids act like pH buffers.
• Characteristics of a region of a protein are a function of amino acid composition.
• Shape is a function of regional characteristics.
• Hidden or partially hidden regions like in three dimensional shapes tend to have weaker characteristics
• The interactions between and within a protein are due to –
  i) hydrophobic linkages
  ii) ionic charges
  iii) Disulfide bonds – these can be easily broken or formed.
  iv) covalent bonds – these hard to form or broken.

Protein water interactions

• Water is associated with proteins and can be described as being one of the following three types -
  i)Free water
  ii)Associated water (bound water)
  iii) Tightly bound water
• The difference between association is the amount of energy it takes to remove the water.
• Water holding and solubility are related to free & bound water.
• Free water removal requires little energy .
• Bound water removal is a difficult task.
• As the charge on protein decreases the hydrophobicity increases and some bound water gets "Free" it
  results in a drip.
• As bound water decreases a protein can move easily interact with another protein.
• At isoelectric point a protein has a pH at which there is no net charge . The positive and negative
  charges are equal.
• At isoelectric point (pI) protein solubility is at a minimum and the hydrophobicity is maximum.
• Near the isoelectric point the proteins tend to fold more tightly.
• The charged proteins tend to fold be repulsive to other as a result they open out and spread.
• Salts change the charges on proteins and thereby the hydrophobic character.
• Changing the salt &/or pH selectively precipitate or solubilizes only one of the two proteins. For
  example — class Concentration Solubility Sarcoplasm 55 mg/ ml 0.05M salt Myofibrillar 115mg/ml
  0.5M Particulate 20 mg/ml N.S.

Protein denaturation

• Anything which makes the protein non functional is denaturation which may result in changes in color,
  solubility etc.
• Cooking causes denaturation of proteins as the input energy leads to covalent bond formation with other
  proteins and carbohydrates. The changes in carbohydrates cause browning.
• Protein structure is irreversibly altered by denaturation caused by solvent, heat, oxidation and may become
  tightly folded or unfolded. For example CHCl3 coagulates hemoglobin and folds causing precipitation
  and this can`t be made soluble again.
• Proteins could be degraded using various proteases by inducing proteolytic effects. Protease degradation
  changes solubility, isoelectric points etc.
• Protease can be endogenous or exogenous.