Molecular anvil

Yaffe MB (2002) How do 14-3-3 proteins work -Gatekeeper phosphorylation and the molecular anvil hypothesis. FEBS Lett 513 53-57... 

THE EXPLANATION OF HIGH SPECIFICITY OF DISCRIMINATING OPTICAL ISOMERS IN ENZYMATIC REACTIONS BY THE MOLECULAR ANVIL MODEL OF ENZYME... 

The author proposed a concept of the molecular anvil in 1979 and in this paper high specificity of enzyme of discriminating optical isomers will be explained by employing the molecular anvil model of enzyme. 

Fig.2 Schematic illustration of four different types of the molecular anvil with one anvil site and number of sites n=5 in simultaneous multisite contact. The dots indicate sites of contact. E. Enzyme. S. Substrate. In comparison single site contact for ordinary molecules is shown together.

Let us next explain how the molecular anvil works. The four different types of molecular anvil shown in Fig.2 can be reduced in principle without loss of intrinsicity to the one shown in Fig.3,... 

Fig.3 Schematic illustration of the molecular anvil with n=5 and one extruded site. Mi, M2 The two interacting molecules, r indicates inter-molecular distance and Aro indicates extruded distance. The arrows indicate direction of force and their length indicates its magnitude.

Let us consider the molecular anvil in which the number of sites in simultaneous multi-site contact is n and the number of anvil sites is one and its extruded distance is Aro- When the two molecules are separated at infinite distance, there is no intermolecular force to exert and the potential energy at this distance is taken to be zero. Then if the two... 

Let us explain this situation more quantitatively. Since the total potential energy of the molecular anvil is the sum of potential energies of the anvil site pair and the rest of the n-1 site pairs, the total potential energy of the molecular anvil is expressed generally as... 

Fig,4 Potential curves for the molecular anvil with n=3 and Aro=0,173ro assuming Lenard-Jones 12-6 type potential function. 

Employing the molecular anvil model described above and making some assumptions for shapes of optical isomers and enzyme molecule, discrimination factor for optical isomers were calculated. 

For enzyme molecule it is assumed that there is a hole on the surface of the enzyme molecule and its size and shape is so chosen that it satisfies the two conditions of formation of the molecular anvil. It is also assumed that enzyme side has the extruded site at the deepest part of the bottom surface as is indicated in Fig,7 by the black dots. 

Calculations were made assuming that the total reactivity is the product of the binding factor and the chemical factor which comes from enhancement action of the molecular anvil The total reactivities are calculated for all configurations and summed for each isomer and their rati-... 

Eo/kT Discrimination ratio (A) with (B) without molecular anvil molecular anvil A/B... 

It is clear from the Table that discrimination ratio with molecular anvil is very high. To make clear the effect of the molecular anvil, discrimination ratios without molecular anvil are shown together for comparison. 

It is clear that improvement of discrimination ratio by molecular anvil goes up as the value of binding energy increases. As for the values of Eo it can be derived from heats of vaporization. Eo is nearly equal to AH 2/z where AH is the value of heat of vaporization and z is the number of nearest neighbours and is between 6 and 12. For heat of vaporization of about 10 K cal. the value of Eo/kT is about 3. For amino acid there is no data of heat of vaporization, but their lattice energy values are of similar order or more, an order of discrimination factor of L-and D-isomer may be explained by this model. 

The molecular anvil model of enz3mie is proposed and it can explain consistently the two distinct features of enzyme, high catalytic power and high specificity. By employing this model discrimination ratios for optical isomer were calculated for various values of binding energy. It is shown that the molecular anvil plays an important role in elevating discrimination factor. 

KAZUO AMAYA / The Molecular Anvil Model of an Enzyme Taking into Consideration the Flexibility of Enzyme Molecules... 

Let us explain how the molecular anvil operates. When the two molecules are separated at distances greater than the equilibrium distance, an attractive force exists between every pair of molecular contacts. However when they come closer to each other, a repulsive force begins to exert only at the anvil site and the other contact sites remain to be attractive. In such a range of distances attractive forces at the contact sites are focused at the anvil site and high pressure is produced at this point and a high energy state is spontaneously created at this anvil point. This is molecular anvil action. 

Fig. 1. Illustrations of various types of molecular anvil for n = 5. a RiSi O. b RjS = 0.

Let us discuss molecular anvil action more quantitatively. The total potential energy of the molecular anvil ,(r) is expressed by assuming pair approximation, that is the total energy is the sum of the energy of each molecular contact pair. 

Fig. 2. Potential energy curves of the molecular anvil for n = 5 with different values of the relatively extruded distance Aro nd its relationship between maximum peak potential energy at the anvil site, E. Figures 2(a)-(c) are curves for values of ro/ro=0, 0.2 and 0.5 respectively. Curves 1, 2 and 3 in each figure indicate the anvil site, the contact sites and the potential energy respectively. Figure 2(d) is the dependence of on Aro.

The peak positive potential energy values at the anvil site for a particular value of the relatively extruded distance Aro varies very sharply with Aro and is shown in Figure 2(d) for n = 5. The maximum value in the curve of this figure E is a function of n and is equal to ( — l) o- Values of Aro/ro corresponding to E vary from 0.153 for = 2, 0.200 for n = 5 and 0.237 for n = 10 and are nearly near 0.2. Since ro is an order of a few A, the molecular anvil has its maximum efficiency for Aro of about 1 A. This means that the efficiency of the molecular anvil is very sensitive to the relative size and shape of the substrate and enzyme molecules. This is the origin of the high specificity of enzymes. 

Fig. 4. Peak (1) and average (2) values of potential energy at the anvil site of the molecular anvil for various values of n with maximum efficiency.

Fig. 5. Dependence of complexation energy, Ec, peak energy at the anvil site, E, and their sum on the relatively extruded distance, Aro > for the molecular anvil with n = 5.

Fig. 6. Energy diagram of an enzymatic reaction showing elevation of starting level of a reactant system by molecular anvil action.

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