What Affects the Activity and Stability of Enzymes?

Wastes processing levels usually dictate some variation in physical conditions under which the enzyme products must function. In order to utilize enzymes to their optimal potential in catalytic ability, we must be familiar with the basic principles that can affect the activity and stability of these enzymes. Enzymes, being biological compounds and being comprised of a high percentage of protein, are subject to many environmental effects. Although the following  principles hold true for most biological enzymes produced for commercial agricultural use:

The pH of the environment has a profound affect on enzyme activity and stability. Activity optimal for pH's of various enzymes vary; however, the optimal pH's for the biological  catalysts produced by most commercial strains of microorganisms lies between pH 4.0 and 7.5. This range is from moderately acidic to mildly alkaline in nature. These are the pH levels normally encountered. Figure 1, indicates a difference in activity levels that various enzymes exhibit at varying pH levels.

Another major affect of enzyme activity and stability is temperature. Since enzymes are biochemical catalysts, made up at least partially of protein, they are sensitive in varying degrees to heat. Raising temperatures of the environment generally multiplies the degree of activity by the enzyme. Once an optimum temperature has been reached, however,  even higher temperatures cause rapid degradation of the enzyme with concurrent and  irreversible loss in activity. Optimal temperatures generally range from 98 °F to 140 °F (37 °C to 60 °C) for most hydrolytic enzymes. High temperatures (over 150 °F, 66 °C) generally have detrimental effects on the enzymes. However, there is broad variation in resistance  and sensitivity to heat among the enzymes' types. Bacterial  enzymes such as those from Bacillus subtilis are less sensitive to heat than are the fungal enzymes of A oryzae. Some amylase preparations prepared by the fermentation of Bacillus species can withstand even boiling for short periods and have optimal activities in the 158 °F - 176 °F (70 °C - 80 °C) range. Our laboratory has determined that approximately 85% of the activity from Bacillus subtilis/licheniformis alpha-amylase survives high heat. A. oryzae amylases, however, showed a greater than 90% loss activity in high heat. When the enzyme-bearing, dried fermentation products of these two microorganisms are kept dry, they are much more resistant to environmental temperature stress than if they are moistened. In fact, very few stability problems are encountered with most enzymes  in typical situations.

Basic Knowledge of Enzymes Applied

Making use of general knowledge about enzymes including how they act, under what conditions they perform, and how to preserve their activity is important in applying the technology of enzymes to organic waste digestion.

Helpful References on Enzymes:

Aunstrup, K. 1979. In Enzyme Technology, L.B. Wingard, Jr., E. Katchalek-Katzir,
L. Goldstein (ed). Academic Press, Inc., New York.

Boyer, P.D. (ed). 1971. The enzymes, 3rd, ed. Vol. 5. Academic Press, Inc., New York.

Fogarty, W. M. 1974. Enzyme technology - projects and developments. In Projects and prospects in industrial fermentation: proceedings of meeting held in Holly Royde. A. J. Powell and J. D. Bu'Lock (ed). U. of Manchester. Manchester, England.

Godfrey, T. and J. Reichelt (eds). 1983. Industrial enzymology: the application of
enzymes in industry. Nature Press. New York.

Kulp, K. 1975. Carbohydrases and other enzymes.