Page 28 - Enzymes in Tropical Soils

16 Enzymes In Tropical Soils

the rate of a biochemical reaction so that the reaction products may be highly
available. Every enzyme also works on a specific substance and does not work on
any other substances. For example, phosphatase works on the decomposition of
organic P and does not work on any other organic compounds without P in their
structures. The presence of any other soil enzymes may not disturb the stability of
organic P. The detachment of P from any organic P structures may progress very
slowly and the reaction products may not suffice the amount needed by a fast
growing plant. The specificity of enzyme can be described in Fig. 2.1.

2.2 Working Mechanism of Enzymes

The theory of enzyme action proposed by Michaelis and Menten (1913 in
Tabatabai, 1982) is mathematically expressed in Eq. 2.1. An enzyme and a
substrate molecules form a complex of enzyme-substrate, which is unstable (Fig.
2.1). The unstable complex will then pass through several steps to form a new
molecule called product molecules and enzyme molecule. After the biochemical
reaction, the enzyme molecule returns to its original form, meaning that the
enzyme participates in the biochemical reaction but it does not react with any
molecules. The enzyme action is described in Eq. 2.1 as follows.

S + E  ES  E + P ....... Eq.2.1

where S is a substrate molecule, E is an enzyme molecule, ES is an intermediate
enzyme-substrate complex, and P is the product of the biochemical reaction. The
enzymatic reaction is controlled by the rate constants k 1 , k 2 , and k 3 ; where k 1
controls the formation of ES complex, k 2 controls the dissociation of ES forming S
and E, and k 3 controls the formation of E and P.
As cited by Tabatabai (1982) the rate of enzyme reaction is controlled by
several important factors, among which are: (a) the concentration of substrate, (b)
the concentration of enzyme, (c) temperature, and (4) pH. The concentration of
substrate is very important for enzyme to act. The rate of the a biochemical
reaction increases with the increase in substrate concentration until a value at high
concentration after which the addition of the substrate does not affect the rate of
the reaction. At this concentration, the rates of the reaction is maximum and
independent of the substrate concentration, but is dependent on the
concentration of enzyme.

Abdul Kadir Salam - 2014