Tetrameric molecule

Hemoglobin is a tetramer built up of two copies each of two different polypeptide chains, a- and (5-globin chains in normal adults. Each of the four chains has the globin fold with a heme pocket. Residue 6 in the p chain is on the surface of a helix A, and it is also on the surface of the tetrameric molecule (Figure 3.13). 

Figure S.8 Schematic view down the fourfold axis of the tetrameric molecule of neuraminidase as It appeared on the cover of Nature, May 5, 1983.

The transitions between these states in each tetrameric molecule are concerted, in other words all four subunits of each molecule are in the same state, either R or T. 

The K+ channel is a tetrameric molecule with one ion pore in the interface between the four subunits... 

All K channels are tetrameric molecules. There are two closely related varieties of subunits for K channels, those containing two membrane-spanning helices and those containing six. However, residues that build up the ion channel. Including the pore helix and the inner helix, show a strong sequence similarity among all K+ channels. Consequently, the structural features and the mechanism for ion selectivity and conductance described for the bacterial K+ channel in all probability also apply for K+ channels in plant and animal cells. 

Figure 16.13 Structures of some tetrahalides of Se and Te (a) Sep4 (gas), (b) crystalline Sep4, and schematic representation of the association of the pseudo-tbp molecules (see text), (c) coordination environment of Te in crystalline Tep4 and schematic representation of the polymerized square pyramidal units, (d) the tetrameric unit in crystalline (TeCl4)4, and (e) two representations of the tetrameric molecules in Te4li6 showing the shared edges of the Telg octahedral subunits.

Beck, J. and Strahle, J. (1986) Synthesis and structure of 1,3-Diphenyltriazenidogold (I), a tetrameric molecule with short gold-gold distances. Angewandte Chemie (International Edition in English),... 

The structure of an antibody is normally depicted as a capital letter Y configuration. IgG is the most predominant antibody. It is a tetrameric molecule consisting of two identical heavy (H) polypeptide chains of about 440 amino acids and two identical light (L) polypeptide chains of about 220 amino acids (Fig. 4.1).The four chains are held together by disulfide bonds and noncovalent interactions. 

As expected, bands which do shift upon lithium isotopic substitution were found below 625 cm (Table 2) and their appearance at such low wavenumbers is consistent with their assignment to complex vibrations of the tetrameric molecules. 

With our present knowledge, we often cannot understand, let alone predict, the more profound details concerning the kind of linking. Why does BiF5 form linear, polymeric chains, SbF5 tetrameric molecules and AsF, monomeric molecules Why are there chloro and not sulfur bridges in (WSCl4)2 Why does no modification of TiO, exist which has the quartz structure ... 

Quadniply bonded dinuclear compounds also can dimerize to give tetrameric molecules ... 

The structure of the tetrameric molecule of aluminium isopropoxide containing the metal atoms with 2 types of coordination — octahedral and tetrahedral — has been predicted by Bradley and then confirmed by the NMR data The X-ray single crystal study has shown that the central and the three peripheric aluminium atoms are situated in the same plane perpendicular to the main trigonal axis, which goes through the central atom. The 3 [A1202] 4-member cycles are situated in the mutually perpendicular planes [1642, 574] (Fig. 4.8 b). 

On addition of PrOH to the crystals it is possible first to obtain very concentrated solutions, from which then commences the crystallization of poorly soluble tetrameric form (Fig. 6.2). It can be supposed that the trimer molecule coordinates an additional alcohol molecule along the sixth coordinate of the central aluminum metal in solution and then forms with the aid of hydrogen bonding the intermediates, which transform subsequently into tetrameric molecules already containing the hcxacoordi nated central A1 atom. The incomplete coordination polyhedron ofthe A1 atom is thus responsible for the thermodynamic instability ofthe phase, where it is present [1642],... 

Two active centers are formed at the interface of two subunits, building up one dimer such that the a-domain of one subunit interacts with the y-domain of the second subunit and vice versa. The interface between the two dimeric halves of the tetrameric molecule is not directly involved in the catalytic center. 

Fig. 1. A schematic representation of hemoglobin indicatinga tetrameric molecule consisting of two a and two 3 chains, each containing a heme group. [From Dickerson and Geis (1969) illustration copyright by I. Geis],...

The three-dimensional and primary structures of the closely related enzyme, tyrosine phenol-lyase, have recently been determined.28 Since 43% of the amino acid sequences of this enzyme and tryptophanase is identical, their three-dimensional structures should be very similar. The structure of the lyase is like a butterfly. The tetrameric molecule can be considered from a crystallographic point of view as an a2a 2-structure consisting of two... 

Exercise A1.2. Discuss the energetic implications of the facts that elemental P exists as tetrameric molecules or as sheet-like extended structures under normal conditions but N is found as diatomic molecules. Focus your discussion on the relative energetics of E-E single vs. E=E triple bond energies for E = N, P. 

Symbol for the toxic element that, like phosphorus and antimony, forms tetrameric molecules when uncombined with other elements (split the letters of the symbol as shown). 

Fig. 3. Tetrameric molecules in the crystal structures of d-Tel, (left) and y-Tel4 (right) with bond lengths (A) 228,363).

---