Head interaction

The diffraction data were also used to guide the selection of the best preserved e.m. images of decorated actin which were then used for a 3-D reconstruction (Amos et al., 1982). In this work, it was suggested that a myosin head interacts with two actin monomers (while still retaining a 1 1 stoichiometry), but this point has not been proved definitively. 

When soap is dispersed in a nonpolar phase, inverted micelles are formed in which the nonpolar tails of the soap molecules interact with the bulk solvent while the hydrophilic heads interact with each other. This behavior of amphiphilic molecules explains how they can disperse nonpolar particles in water the hydrocarbon tail of the amphiphile interacts with the particle, such as an oil droplet, dirt, or a lipoprotein membrane fragment, covers the particle, and then presents its hydrophilic head groups to the aqueous phase. 

Other major differences between kinesins and myosin II heads involve kinetics180 181 and processivity.173 Dimeric kinesin is a processive molecule. It moves rapidly along microtubules in 8-nm steps but remains attached.182 1823 Myosins V and VI are also proces-sive1 83, a3e but myosin II is not. It binds, pulls on actin, and then releases it. The many myosin heads interacting with each actin filament accomplish muscle contraction with a high velocity in spite of the short time of attachment. Ned and Kar3 are also nonprocessive and slower than the plus end-oriented kinesins.184... 

Figure 3. The arrows indicate how the local dipoles of the H-bonds might interact with the local dipoles of the p- and m-nitroanilines to give head to tail and head to head interactions. The + and - signs indicate centers of charge. Unmarked carbon atoms are neutral.

The surface area per polar head is mainly determined by head interaction and is itself the sum of van der Waals attraction and electrostatic repulsion and can be... 

In general, asymmetric shapes achieve the best packing in the crystal by introducing a center of symmetry (Figure 11 a). The necessity, in many cases, of a screw axis may arise from the presence in the molecule of a tail and a head , caused by a displacement between the centers of negative- and positive-charge distribution. Thus, in order to have the maximum number of tail-to-head interactions, it is necessary to introduce a screw axis besides the center of symmetry (Figure 11 b). 

Figure 11. Asymmetric shapes achieving the best packing in a crystal by introducing (a) a center of symmetry and (b) screw axis, the latter induced by the need of having the maximum number of "tail to head" interactions (see text).

The three dimensional form can be best visualised as a swiss roll, where jam represents the water and the sponge is the lipid layer with the polar head interacting with the water. These structures are important in the stabilisation of doughs and batters and in particular in promoting foam stabilisation at the air / water interface. 

Figure 34.24 Krnesin moving along a microtubule. (1) One head of a two-headed kinesin molecule, initially with both heads in the ADP form, binds to a microtubule. (2) The release of ADP and the binding of ATP results in a conformational change that locks the head to the microtubule and pulls the neck linker (orange) to the head domain, throwing the second domain toward the plus end of the microtubule. (3) ATP undergoes hydrolysis while the second head interacts with the microtubule.

Hydrotropy When there are strong chain-chain and head-head interactions between surfactant molecules (due to long, straight chains and close-packed heads), either insoluble crystal formation (low Krafft point, p. 214) or liquid-crystal formation (Chapter 3, Section IIC) may occur. Since there is much less space available for solubilization in rigid liquid-crystal structures than in the more flexible types of micelles, the onset of crystal formation usually limits the solubilization capacity of the solution. The tendency to form crystalline structures can be reduced by the addition of certain nonsurfactant organic additives called hydrotropes. 

The results of domain swap experiments, in which an extracellular domain of one kind of cadherin is replaced with the corresponding domain of a different cadherin, have indicated that the specificity of binding resides, at least in part, in the most distal extracellular domtiin, the N-terminal domain. In the past, cadherin-mediated adhesion was commonly thought to require only head-to-head Interactions between the N-terminal domains of cadherin oligomers on adjacent cells, as depicted in Figure 6-3. However, the results of some experiments suggest that under some experimental conditions at least three cadherin domains from each molecule, not just the N-terminal domains, participate by inter-digitation in trans associations. 

The model used by Care and coworkers [30-32] uses only nearest-neighbor interactions on a cubic lattice, i.e., the coordination number z — 6. Note that the numbers of all pair contacts in a lattice system can be specified using only three independent contact parameters, since there are only six possible bead-bead interactions among the three different beads. Desplat and Care [31] chose the three independent contact parameters to be tail-solvent, head-solvent, and head-head interactions. The total dimensionless energy of the system, jS , can then be written as... 

This is a typical structure for many chain polymers, i.e. PE, PVC, PTFE, but can also occur with step polymerizations, e.g. polyethers (starting from cyclic ethers) and polysiloxanes (starting from R2SiCl2). Normally head-to-tail combination occurs in vinyl polymerization (Figure 1.1). Rarely does head-to-head interaction occur—exceptions include polyvinyl fluoride (PVF) and polyvinylidene difluoride (PVDF) where 20% head-to-head polymerization takes place, whereas with polypropylene (PP) < 0.5% occurs. 

C jmylperoxy. The initial reaction between c jmylperoxy radicals (RO2 ) involves a head-to-head interaction to give di-cumyl tetroxide (30)... 

Colloidal suspensions of micelles are kept stable by electrostatic repulsions that occur at their surfaces. For example, in soap, the ionic heads of the soap molecules compose the surface of the spherical particle (Figure 12.24 ). These ionic heads interact strongly with water molecules but repel other colloid particles. Heating a colloid composed of micelles can destroy the micelles because collisions occur with enough force to overcome the electrostatic repulsions and allow the molecules within the micelles to coalesce with those in other micelles. Similarly, adding an electrolyte to a colloidal suspension of micelles can also disrupt the electrostatic repulsions that occur between the particles and thus destroy the colloid. For this reason, soap does not work well in a salt water solution. 

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