Propeller loops

A second example of up-and-down p sheets is the protein neuraminidase from influenza virus. Here the packing of the sheets is different from that in RBP. They do not form a simple barrel but instead six small sheets, each with four P strands, which are arranged like the blades of a six-bladed propeller. Loop regions between the p strands form the active site in the middle of one side of the propeller. Other similar structures are known with different numbers of the same motif arranged like propellers with different numbers of blades such as the G-proteins discussed in Chapter 13. 

Loop air-lift pressure cycle propeller loop jet loop... 

A schematic of the propeller loop reactor is shown in Fig. 37. In this case, the circulation flow of the fluid phases is created by a hydromechanical propeller flow drive. The use of a draft tube often improves the mass and heat transfer efficiency in these reactors (Blenke, 1967). This type of reactor involves complicated construction and leads to operating problems related to the sealing of the shaft. It is not suitable for biosystems due to possible damage to sensitive organisms in the high shear fields at the propeller. However, it is especially suitable for highly viscous polymeric fluids and for medium-size units. 

Design parameters for novel reactors such as rotating-cylinder reactors, thin-film reactors, propeller loop reactors, screw reactors, and multidisk reac-... 

This concept for the determination of the effective viscosity for mixing processes is also transferable to stirred vessels, because in the laminar flow range the above circumstances also apply for propeller loop reactors [351]. This was proved with tanks with pitched-blade stirrers [540]. The nO values could be better correlated with RSefr numbers, which were produced according to expression (3.25), than those which contained ft g according to expression (1.45) after Metzner-Otto. 

Stirred tank Multistage (or cascade) Propeller loop... 

The propeller loop reactor with internal draft tube cum heat exchanger configuration has also been used by the author for an extremely exothermic (almost explosive) solid-liquid reaction ... 

Axial-Flow (Propeller) Pumps (Fig. 10-44) These pumps are essentiahy very-high-capacity low-head units. Normally they are designed for flows in excess of 450 mVh (2000 gal/min) against heads of 15 m (50 ft) or less. They are used to great advantage in closed-loop circulation systems in which the pump casing becomes merely an elbow in the line. A common installation is for calandria circulation. A charac teristic cui ve of an axial-flow pump is given in Fig. 10-45. 

Figure S.7 The subunit structure of the neuraminidase headpiece (residues 84-469) from influenza virus is built up from six similar, consecutive motifs of four up-and-down antiparallel fi strands (Figure 5.6). Each such motif has been called a propeller blade and the whole subunit stmcture a six-blade propeller. The motifs are connected by loop regions from p strand 4 in one motif to p strand 1 in the next motif. The schematic diagram (a) is viewed down an approximate sixfold axis that relates the centers of the motifs. Four such six-blade propeller subunits are present in each complete neuraminidase molecule (see Figure 5.8). In the topological diagram (b) the yellow loop that connects the N-terminal P strand to the first P strand of motif 1 is not to scale. In the folded structure it is about the same length as the other loops that connect the motifs. (Adapted from J. Varghese et al.. Nature 303 35-40, 1983.)...

Figure 5.9 The six four-stranded motifs in a single subunit of neuraminidase form the six blades of a propeller-like structure. A schematic diagram of the subunit structure shows the propeller viewed from its side (a). An idealized propeller structure viewed from the side to highlight the position of the active site is shown in (b). The loop regions that connect the motifs (red in b) in combination with the loops that connect strands 2 and 3 within the motifs (green in b) form a wide funnel-shaped active site pocket, [(a) Adapted from P. Colman et ah, Nature 326 358-363, 1987.]...

The second protein in the membrane of influenza vims, neuraminidase, does not belong to any of these three groups of barrel structures. Instead, it forms a propeller-like structure of 24 p strands, arranged in six similar motifs that form the six blades of the propeller. Each motif is a p sheet of 4 up-and-down-connected p strands. The enzyme active site is formed by loop regions on one side of the propeller. 

In the complex with Gpy the two phosducin domains do not interact with each other, instead they wrap around the edge and the top side of the p propeller, to form an extensive interaction surface (Figure 13.17). The N-terminal domain of phosducin interacts with all of the top loops of the p propeller including part of the surface of Cpythat interacts with Gq (Figures 13.15 and 13.17). This interface between phosducin s N-terminal domain and Gpy clearly precludes association of the latter with Gq. 

The DTB, crystallizer has a relatively slow-speed propeller agitator located within a draft-tube which draws a fine-crystal suspension up to a boiling zone of wide cross-sectional area, as shown in Figure 3.3(i). The fine-crystal magma then passes through an annular zone in which an additional baffle is located. Liquor flow continues upwards at low velocity while crystals settle out and fall to the base of the vessel. Liquor from the external pumped loop provides an up-... 

A so-called Rosett cell can be fitted with a flanged lid (Fig. 7.12). The design of the Rosett cell allows the irradiated reaction mixture to be sonically propelled from the end of the probe around the loops of the vessel and thus provides both cooling (when the vessel is immersed in a thermostatted bath) and efficient mixing. A PTFE sleeve provides a vapour tight fit between the probe and the glass joint. 

The structure of the C-domain of hemopexin was determined first (128). The structure is a four-hladed p-propeller (Fig. 7), the smallest P-propeller known, and serves as the paradigm for the several proteins known to have a pexin domain, including vitronectin (108), and several metalloproteinases (107). The repeats evident in the sequence of hemopexin (99-101), for instance DAAV/F motifs and WD repeat, form a large part of the p-strands of the four blades, which are connected by short loops and a-helices. 

Fig. 3.23. Conductivity cell with phial magazine Q containing phials and magnetic pusher. The electrode assembly E is that shown in Fig. 3.22. S is a stirrer shaft with a propeller at one end and a glass-enclosed magnet N at the other. The stirrer shaft is held in position by the PTFE bearings Tf Tf, and Tf and the glass tube spacer G Th ha. thermocouple pocket and B a magnetic breaker for the phial P. The propeller, driven by the rotating magnet M, pumps the cell contents around the loop L, so that when P is broken there is very fast mixing.

Fig. 2. Structure of the ABLl kinase portion of the BCR-ABLl protein. The activation loop (blue) is in the closed (inactive) conformation on the left and in the open (active) conformation on the right. A molecule of imatinib is positioned in the ATP-binding site and is in green. (Reprinted with permission from U S. Healthcare Communications, LLC. LitzowMR, Tefferi A. Chronic myeloid leukemia problems propel progress. Amer J Hematol/Oncol, 2007 6(5) supplement 7 19-22).

Turbine pumps mix features of a simple propeller (axial flow) pump with a centrifugal pump and are often referred to as units with mixed flow. A simple turbine pump carries curved vanes on a central rotating spindle. Such pumps are often immersed in the liquid and find use in closed-loop circulation systems, in condenser circulating water, and in sumps and wells. Turbine pumps have noteworthy pumping capacity, and like positive displacements pumps are often used for heads up to about 100 ft/stage with capacities of up to several hundred gallons/minute. 

Mixing time is inversely proportional to the average circulation velocity near the wall (in the case of the flat-blade turbine) or near the surface (upflow propeller) or, in other words, where the longest circulation loop exists,... 

---