Crystal structures vitamin

Figure 13 (Plate 9). Crystal structure of the BtuC2D2 complex involved in the uptake of vitamin Bi2. Two copies of the polytopic integral membrane protein BtuC and of the ATPase subunit BtuD are shown, together with bound ATP (reproduced by permission of K. Locher). For more details see the text...

Karpowich, N. K., Huang, H. H., Smith, P. C. and Hunt, J. F. (2003). Crystal structures of the BtuF periplasmic-binding protein for vitamin B12 suggest a functionally important reduction in protein mobility upon ligand binding, J. Biol. Chem., 278, 8429-8434. 

An X-ray crystal structure determination of calciferol (vitamin D-2,71) showed that steric crowding in the s-cis diene system resulted in a twisted conformation with a dihedral angle of 53° [59], On irradiation with a mercury lamp, it was partially converted into ergosterol (72) and tachysterol (73) [60, 61]. When a solution of calciferol in light petroleum containing a trace of iodine was exposed to diffuse daylight, the vitamin was photoisomerized to (74) [62],... 

Ascorbic acid ( Vitamin C ). The crystal structure of this substance cannot be said to be established with the certainty and precision we associate with those already described nevertheless, there is no reason to doubt that the structure suggested by Cox and Goodwin (1936) on the basis of p, limited study of the X-ray reflections is essentially correct. The work is described here because this crystal structure presents some very interesting and instructive features. It is also historically interesting because a preliminary study by optical and X-ray methods played a part in the elucidation of the chemical structure of this biologically important substance. (Cox, 1932 a Cox, Hirst, and Reynolds, 1932 Cox and Hirst, 1933.)... 

The structures of the biologically active forms of B12 were solved relatively recently (1961) (78) and were shown to contain a cobalt atom surrounded by a corrin ring as shown in Fig. 16 (80). The crystal structure also showed a cobalt-carbon a bond which was quite surprising since the few compounds with cobalt-carbon a- bonds known at that time were quite unstable (79). The corrin ring is similar to the porphyrin ring, but its greater saturation imports less rigidity than the porphyrin. Corrinoids with the axial 5,6-dimethylbenzimidazole substituent are called cobalamins. Vitamin B12 with Co(III) and CN in the top axial position is... 

Dorothy Crowfoot Hodgkin X-ray crystal structure of vitamin B12... 

Hodgkin, D.C., Pickworth, J., Robertson, J.H., Trueblood, K.N., Prosen, R.J. and White, J.G. (1955) Structure of vitamin B12. The crystal structure of the hexacar-boxylic acid derived from B12 and the molecular structure of the vitamin. Nature, 176,... 

Kennard, O. Allen, F. Watson, D. (1977) Molecular structure and dimensions guide to the literature 1935-1976, organic and organometallic crystal structures. Utrecht Bohn, Scheltema and Holkema 209Sebrell, W. Harris, R. (1967) The Vitamins, 2nd ed. vol. 1. NY Academic Press, pg. 12. 

Fig. 25.1. Possible movements of the water molecules between the main water networks I and II in the channel region in the crystal structure of vitamin B12. O, Water network I , water network II, >, movements I— 11 - movements II— 1 [880]...

In macromolecular crystallography, this process cannot be observed because hydrogen atoms are not located and dynamic processes cannot be seen . However, in the crystal structure of vitamin B12 studied by X-ray and neutron diffraction methods, an interpretation of the water movement could be derived [127, 880, 881]. 

In this crystal structure, the vitamin B12 molecules are well ordered (except for a side chain). Between the molecules there are wide channels which are filled with four acetone and with a total of >140 mostly disordered water molecules in the unit cell. Careful analysis of X-ray and neutron diffraction data suggested that the disorder can be described in terms of a movement of water molecules within the wide channels, as indicated schematically in Fig. 25.1. According to this interpretation, there exist two dynamically related water networks I (atoms in circles) and II (atoms in squares). Starting with network I, a water molecule can be either pushed into the asymmetric unit at position 410 (path A) or pulled out at position 228 (path B). If water molecule 228 is pulled out and moves into position 410 in the adjacent asymmetric unit, water 222 is pulled towards 428 and the void is filled by consecutive movements of water molecules 231, 226, 410 into positions 431, 227, 210. These movements are consistent with a transition from network I into network II. Conversely, if a water molecule enters the asymmetric unit through path A, then water molecules 210, 431, and 428 of network II move into positions... 

We can envisage that this description of water movement along functional groups is not limited to the crystal structure of vitamin B12 but that it occurs generally in the hydration of biological macromolecules. If so, the concept of... 

Tocchini-Valentini, G., Rochei, N., WuRTZ, J. M., Mitschler, A., Moras, D. Crystal structures of the vitamin D receptor complexed to superagonist 20-epi ligands. PNAS 2001, 98, 5491-5496. 

A., Kiaholz, B., Moras, D., The crystal structure of the nuclear receptor for vitamin D bound to its natural ligand. Mol. Cell 2000, 5. 173-179. 

Even in his mid-80s, and without Ava Helen, Pauling continued to travel extensively, speak widely, and publish regularly on topics from crystal structure to nuclear physics, superconductivity to human metabolism, chemical bonding to world peace. He never stopped receiving awards and honorary doctorates, or advocating vitamin C. 

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