Potassium structural data

Reaction of [Os(en)3]I3 with three, two or one moles of potassium amide yields respectively the brown Os(en — H)3, the yellow-brown [Os(en — H)2en]I and the pink [Os(en — H)(en)2]I2 the magnetic moment of the latter is 1.58 BM at room temperature.82 Formulation as iminato complexes would also be possible structural data on these species would be of interest. 

The crystal stmctures of several sodium- and potassium-activated enzymes have now been determined and the position of the monovalent cation estabhshed. Structural data are listed in the Protein Data Bank (PDB). They provide a clue (but not an absolute proof) to their location within the enzyme on activation. Further biochemical studies may be necessary to verify this finding. Some examples of these structures are presented here. The first example (thrombin) is a sodium-activated enzyme, but the others are potassium-activated enzymes. 

Several methods for the isolation of PBS have been established [81,104,105,138]. Principally they are based on the observation that PBS are only stable in solutions of high ionic strength, e.g. 0.75-0.9 M potassium phosphate. The PBS are detached from the membranes with 2% Triton X-100. The function of the intact PBS is tested by fluorescence emission spectra at 680 nm upon excitation at 550-650 nm. Most of the structural data describing the PBS originate from the hemidis-coidal type, as reviewed in Refs. 1,77 and 79-86. The complex architecture of the PBS rods and core is best described for the PBS of the cyanobacterium Synechococcus 6301 (a cyanobacterium which contains C-PC but neither PEC nor C-PE in the rods) with a bicylindrical core and for the PBS of the cyanobacterium Syne-chocystis 6701 (which contains C-PC and C-PE in the rods) with a tricylindrical core (reviewed in Refs. 1, 139 and 140). Each cylinder in the core is formed by four complexes of APC trimers with linker polypeptides cylinder A,... 

The trans-tram forms occur in the crystals of cesium hexasulfide (5) and of (rans-dichloro-dien-cobalt(III) hexathionate monohydrate (107), and the ds-ds forms in the crystals of potassium barium hexathionate (102), these being the only compounds containing tetrasulfide groups for which structural data are available. 

Detailed structural data are only available for a few highly selective charmels. The best characterized is the model system gramicidin, which has been elucidated using NMR-based techniques [14,15]. Among physiological systems, atomic level resolution structures (based on x-ray or cryoelectron microscopy) are available for a potassium channel from S. lividans (KcsA) [5], two prokargotic chloride channels [16], a stretch activated channel from M. tuberculosis [17], human red cell aquaporin-1 [18], and a glycerol facilitator from... 

Structural data, indicating the existence of columnar and even disc-like mesophases for the anhydrous alkali, alkaline earth, and cadmium salts of long-chain fatty acids were first reported by Skoulios et al. [9]. For example the potassium ssdts can be lamellar, ribbon-like or disc-like in a three dimensional lattice [33], see Fig. 1. 

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