Meander region

Figure 3.9. A side view showing the overall fold of modified CYP2C5. The largest insertions of additional polypeptide chain relative to prokaryotic P450s occur for the N-terminal region depicted in Figure 3.8, the meander region, and between helices F and G. The latter exhibits two short helical regions labeled F and G. ...

Zheng, Y.-M., M.B. Fisher, N. Yokotani, Y. Fujii-Kuriyama, and A.E. Rettie (1998). Identification of a meander region proline residue critical for heme binding to cytochrome P450 Implications for the catalytic function of human CYP4B1. Biochemistry 37, 12847-12851. 

The structure of the ALR2 holoenzyme showed that the catalytic site was situated atop the nicotinamide moiety of the NADPH cofactor. The substrate binding site, which would determine the enzyme s specificity and also presumably bind inhibitors, appeared to be composed of a deep cleft (Figures 3 and 4). It extended away from the catalytic site towards the loop composed of residues between (34 and cc4 and the last 20 residues of the carboxy-terminal meander. This hypothesis was supported by the appearance of poorly resolved density that occupied this region, which suggested the presence of an endogenously bound substrate or inhibitor in the structure of the holoenzyme [16]. Subsequent studies indicate that this electron density may be a citrate molecule, one of the components included in the crystallization mixture. Activity studies indicate that citrate is indeed one of the many inhibitors of the enzyme with a K in the millimolar range [23]. 

Fig. 4. Direct tomographic, energy-dispersive X-ray diffraction imaging system. Suitcase enters device at left of Figure where spatial landmarks for registration purposes are measured by pre-scanner. In main housing centre-right of Figure, a primary cone-beam executes a meander scan, either of a region-of-interest or suitcase in its entirety. Illustration courtesy of GE Security, Germany.

Figure 2.2 Streamlines of a meandering jet surrounded by recirculation zones showing typical structures in steady two-dimensional flows elliptic (E) and hyperbolic (H) stagnation points, flow regions with open and closed streamlines and separatrices that connect hyperbolic points. The flow is defined by the streamfunction ip(x, y) = Cy — tanh[(y — Acosx)/(Ly/1 + A2 sinx2)].

It is important to stress that the above three descriptions of the spiral wave practically coincide far away from the rotation center. Moreover, already at a relatively small distance ta from the rotation center, the Archimedean spiral becomes very close to the curvature affected spiral obtained from Eq. (9.3), as can bee seen in Fig. 9.1(d). In this example ta can be estimated as ss 9.0 A. Recent computations performed with the Oregonator model [40] and experiments with the BZ reaction [43] also confirm that an Archimedean spiral provides a suitable approximation of the wave front except in a relatively small region of radius A near the rotation center. Even the shape of a slightly meandering spiral waves exhibits only small oscillations around an Archimedean shape, and the amplitude of these oscillations vanishes very quickly with r [44]. Therefore, the Archimedean spiral approximation will be used below to specify the shape of the wave front. 

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