P-meander

The P structure is one of the most important secondary structures in proteins. It occurs in about 80% of the soluble globular proteins whose structures have been determined. In many cases almost the entire protein is made up of P structure. Single strands of extended polypeptide chain are sometimes present within globular proteins but more often a chain folds back on itself to form a hairpin loop. A second fold may be added to form an antiparallel "P meander"102 and additional folds to form P sheets. Beta structures are found in silk fibers (Box 2-B) as well as in soluble proteins. 

When a third strand is added, the relative frequencies of occurrence of the possible motifs reflect the same preferences for antiparallel compared with parallel, and for sequential strands to be adjacent in the structure. Tkble 15.3 shows the possible topologies for three consecutive strands that are adjacent in the same P sheet and their frequency of occurrence in our data set. The most commonly occurring pattern is the P meander (Figure 15.15), which consists of two consecutive P hairpin ( 4-1 ) connections. Many of these meanders exist as isolated units, i.e. no other strands are... 

The OtOt unit, the pap unit, the p-meander, the Greek key, and the p-barrel. 

P-strand) and therefore protein folds. For example, lactate dehydrogenase (LDH) and NADH peroxidase (NHPOx) shares the common FAD/NAD binding motif (GxGxxG). The conversion of a connector helix C in LDH with 3 stranded P-meander (2 ERYEGDGRVQKVVTDKNAY in NHPOx) in NHPOx results in different PPa architecture (versus apa) and thus different folds for these homologs. 

Analysis of known protein stmctures has demonstrated that regular elements can exist in combined forms. Examples are the coiled-coil a-helix (Fig. 1.25, a), chain segments with antiparallel P-stmctures (P-meander stmcture Fig. 1.25, b) and combinations of a-helix and P-stmcture (e. g., PaPaP Fig. 1.25 c). 

Fig. 1.25. Superhelix secondary structure (according to Schulz and Schirmer, 1979). a coiled-coil a-helix, b p-meander, c papap-structure...

The effects of Flix sediment pollution on invertebrates were examined at two levels. Local populations of zebra mussels and crayfish (P. clarkii) were sampled right over the Flix residue sediment, across the reservoir, in a meander immediately downstream the dam and in Asco, in addition to the Riba-roja reference site (Fig. 5a, b). Results from a battery of biochemical biomarkers (Fig. 5c) were similar... 

Frequently recurring substructures or folds are collectively termed supersecondary structures or motifs. These are combinations of a and/or j8 structure. A simple example is a /8 hairpin, consisting of two antiparallel strands joined by a loop of three to five residues (Figure 1.12). This frequently occurs in antiparallel P sheet. Such sheet frequently contains four p strands connected as in Figure 1.13 in a motif called a Greek key (or meander, which is the Greek word for the pattern) because it is reminiscent of the Greek decorative motif, or six strands described as a jellyroll. 

M 67] [P 59] The ratio of the maximum velocity in a zig-zag channel normalized by the maximum velocity in a straight channel was calculated as a function of the number of zig-zag turns for various meandering ratios [59], Up to about six turns, this ratio increases as a consequence of developing more recirculation zones which restrict the flow path for the non-drculated flow and thus increases the corresponding maximum velocity. 

M 67] [P 59] The mixing efficiency was calculated for various diffusion constants, ranging from 2 10 7tol0 10 7m2s 1 [59], A meandering ratio of4 was assumed... 

M 67] [P 59] The mixing efficiency was derived experimentally in a device with a meandering ratio of 8, i.e. a periodic step of800 pm [59], The channels were 100 pm wide and 48 pm deep with a linear distance of2000 pm. An aqueous buffer solution and a buffer solution with fluorescein were contacted the fluorescence intensity was measured at the end of the channel. Owing to the known problems of biasing... 

M 70b] [P 63] Photometric concentration profiles were obtained for mixing of 50 mW reactant solutions at 25 °C and K = 246 in a meander micro mixer close to the inlet (see Figure 1.153) [47]. At the start of the mixing process only one lamella is visible, corresponding to about 10 mM reaction product. Further downstream, the next profiles provide a multitude of lamellae, which represent between 2 and 24 mM product. At still further positions in the meander channel, more homogeneous flow patterns are yielded and the product content is increased to between 15 and 28 mM. Finally, the concentration increases to values close to 50 mM which indicates complete mixing. 

P. Balan, ed. Monumenta reformations lutheranae e tabulariis secretioribus s. sedis, 1521-25 (Regensburg, 1884), 31, and P. Kalkoff, ed. and trans., Die Depeschen des Nuntius Meander vom Wormser Reichstage, 1521 (Halle, 1886), 29. 

To my sister-in-law, Mrs. P. Blair, I owe a special debt of thanks for translating my meandering manuscript into a faultless typescript. My obligations to my wife are too personal to be detailed but too real to be overlooked. 

D.M. Fries, S. Waelchli, P. Rudolf von Rohr, Gas-liquid two-phase flow in meandering microchannels, Chem. Eng. J. 135 (2008) S37. 

Safety professionals, managers, or supervisors who think they can have a significant impact on safety in the workplace by putting on a hard hat and safety shoes and meandering out with a clip-board to make the world safe are really fooling themselves if the upstream processes have not been properly done. Good safety practices must begin as far upstream as possible [p. 10]. 

Dore V., Tsaoulidis D., Angeli P., 2012. p-PIV investigation of water/ionic liquid plug flow dynamics in meandering microchannels. In proceedings of 16th International Symposium on Applications of Laser Techniques to Fluid Mechanics, 09-12 July, Lisbon, Portugal... 

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