Use of lytic methods

The breakage of cells using non-mechanical methods is attractive in that it offers the prospects of releasing enzymes under conditions that are gentle, do not subject the enzyme to heat or shear, may be very cheap, and are quiet to the user. The methods that are available include osmotic shock, freezing followed by thawing, cold shock, desiccation, enzymic lysis and chemical lysis. Each method has its drawbacks but may be particularly useful under certain specific circumstances.

Certain types of cell can be caused to lyse by osmotic shock. This would be a cheap, gentle and convenient method of releasing enzymes but has not apparently been used on a large scale. Some types of cell may be caused to autolyse, in particular yeasts and Bacillus species. Yeast invertase preparations employed in the industrial manufacture of invert sugars are produced in this manner. Autolysis is a slow process compared with mechanical methods, and microbial contamination is a potential hazard, but it can be used on a very large scale if necessary. Where applicable, dessication may be very useful in the preparation of enzymes on a large scale. The rate of drying is very important in these cases, slow methods being preferred to rapid ones like lyophilisation.

Enzymic lysis using added enzymes has been used widely on the laboratory scale but is less popular for industrial purposes. Lysozyme, from hen egg-white, is the only lytic enzyme available on a commercial scale. It has often used to lyse Gram positive bacteria in an hour at about 50,000 U Kg⁻¹ (dry weight). The chief objection to its use on a large scale is its cost. Where costs are reduced by the use of the relatively inexpensive, lysozyme-rich, dried egg white, a major separation problem may be introduced. Yeast-lytic enzymes from Cytophaga species have been studied in some detail and other lytic enzymes are under development. If significant markets for lytic enzymes are identified, the scale of their production will increase and their cost is likely to decrease.Lysis by acid, alkali, surfactants and solvents can be effective in releasing enzymes, provided that the enzymes are sufficiently robust. Detergents, such as Triton X-100, used alone or in combination with certain chaotropic agents, such as guanidine HCl, are effective in releasing membrane-bound enzymes. However, such materials are costly and may be difficult to remove from the final product.