Adsorption is a very economical procedure for immobilization of enzymes. The stability of the adsorbed enzyme derivative will depend on the strength of the noncovalent bonds formed between the support and the amino acid residues on the surface of the protein. Two principal types of bonds can be formed between the enzyme and the inorganic support and they are electrostatic bonds (charge-charge interaction) and hydrogen bonds. The number and nature of these bonds is controlled by the isoelectric point of the protein, and by pH at which the immobilization occurs as these two factors determine the respective surface charges. The main source of surface charged groups on the protein are lys, arg, asp, and glu residues, which are charged at neutral pH. In addition hydrogen bond interactions may involve the hydroxyl groups of ser and tyr residues and the thiol group from cys residues.
