Isology

FIGURE 6.42 Isologous and heterologous associations between protein subunits. 

Isolieruug,/. isolation insulation. Isolier-vermSgen, n. insulating power, -werk-stoff, m. insulating niaterial. -zustand, m. state of insulation or isolation, isolog, a. isologous, isomer, a. isomeric. 

However, Drago s work contains some cases where a discrepancy is observed between the calculated and experimental AH values. In particular, although the adducts built from methylated Lewis bases (like NMe3 or PMe3) are amenable to Drago s pattern, their isologous ethyl derivatives are not, and no clear explanation has been proposed for this observation. 

The isothiocyanates undergo fundamentally the same addition reactions as the isologous cyanic esters (see p. 153), e.g. 0 C N.C6H6. 

Azanthracene and its derivatives, the isologs of anthracene, undergo photodimerization on exposure of their solutions in ethanol, ether and/or... 

In the case of thieno[3,2-6]thiophene and its selenium isologs also, similar shifts are shown by the two HOMOs. The two HOMOs of some S/Se heterocycles are depicted in Scheme 7. 

Paired interactions. If two subunits are held together with interactions aj and are related by a twofold axis of rotation as shown in Fig. 7-11, we obtain an isologous dimer. Each point such as a in one subunit is related to the same point in the other subunit by reflection through the axis of rotation. In the center, along the twofold axis, points c and c are directly opposite the same points in the other subunit. Figure 7-11... 

Isologous bonding is very important in oligomeric enzymes, and it has been suggested that isologous interactions evolved early. Initially there may not have been much complementarity in the bonding but two... 

Figure 7-11 (A) Isologous bonding between pairs of subunits (B) an "isologous square" arrangement of subunits (C) an apparently "tetrahedral" arrangement of subunits. Note the three twofold axes.

Now consider the association of A and B to form oligomers in which the intrinsic binding constants KAX and Kbx have the same values as in the monomers. Since more enzymes apparently exist as isologous dimers than as any other oligomeric form,116 it is appropriate to consider the behavior of such dimers in some detail. Monod et al. emphasized that both... 

Figure 7-22 Comparison of the interactions in isologous (dihedral) and heterologous (cyclic) square configurations of subunits.

In the isologous tetrahedron (Fig. 7-5) the third set of paired interactions cl must be taken into account. (However, the third interaction constant will not be an association constant of the type represented by Xfl AA and KhkAA but a dimensionless number.) On the other hand, the heterologous square has only a single interaction constant. 

Now consider the binding of one molecule of X to the isologous tetramer with a conformational change in one subunit (Eq. 7-44). We see that one pair of aj interactions and one pair of bk interactions have been... 

Isoenzymes (isozymes) 536, 538 Isoionic point 106 Isolation of compounds 98-108 Isoleucine (He, I) 52s, 539 biosynthesis 540 branched fatty acids from 381 configuration 43 Isologous interactions 337-353 in oligomers 349 - 353 square 352s... 

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