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Figure 4. Hill plot

The kinetic cooperativity can be distinguished from the substrate binding cooperativity (spatial cooperativity by means of homotropic interactions) by means of binding studies, measurements of the initial speed and the determination of the type of conformation (9,12).

In the case of the oligomeric enzymes the kinetic cooperativity is more complex. The interactions between the subunits can influence the rate (speed) of the transition or even alter the three-dimensional structure of the subunits themselves. Weakly coupled subunits generate no sigmoidal substrate saturation curve and in this instance the kinetic cooperativity can be greater or smaller than the corresponding substrate binding cooperativity. This is the case for V2, as it can be seen from the values of h ext.(13).

Strongly coupled subunits result in a sigmoid curve V/S, and the two cooperativities can have opposite signs.

In the case of the monomeric enzymes the kinetic cooperativity takes place by means of interactions between the various conformations (9).

In different concentration ranges of adenine the enzyme exhibits different behavior against thymidine, namely:

- Negative substrate binding cooperativity of the enzyme for dT (Figure 5a). The Km value

100 —

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