Tricorne

A trinuclear system, whose structure was published,555 was formed in high yield by the cyclometalation of a l,3-bis(alkylbenzimidazol-2-yl)benzene ligand, followed by the trimerization of the unit, which possesses a vacant coordination site on the palladium atom and a pendant noncoordinated benzimidazole moiety. The resulting product forms a cup-shaped trimer or tricorn, presented in Figure 46, that includes a molecule of acetonitrile in the crystal structure.556... 

The interphotoreceptor retinoid-binding protein (Borst et al., 1989) functions in the regeneration of rhodopsin in the mammalian visual cycle. It is exclusive to vertebrates yet contains a repeated structure that has been found singly in bacterial and plant tail-specific proteases (TSPc) (Silber et al., 1992) and the archaeal tricorn protease (Tamura et al., 1996). The eukaryotic homologs of TSPc are likely to be inactive as... 

The Tricorn Protease and its Structural and Functional Relationship with Dipeptidyl Peptidase IV... 

Fig. 10.8. S urface representation of the tricorn protease with the ribbon model of one subunit superimposed. The two orthogonal views are along the molecular two-fold and threefold axis, respectively. The six solid spheres indicate the active-site positions.

The arrangement of S965, H746, and the oxyanion hole suggests that the classical steps of peptide-bond hydrolysis follow the sequence of the trypsin-like serine proteases, namely the formation of the tetrahedral adduct, the acyl-enzyme complex, and hydrolysis. Tricorn has been shown to exhibit both tryptic and chymotryp-tic specificities (Tamura et al. 1996a). The X-ray structure reveals that specificity for basic PI residues is conferred by D936 which is provided by the diad-related subunit (see Figures 10.9 and 10.10). 

Similarly, there is evidence for functional but not physical interaction of tricorn with the proteasome (Tamura et al. 1998) A physical interaction between these molecules by aligning their respective central pores would imply a symmetry mismatch. While such a physical interaction would be consistent with the geometric dimensions of both molecules, its existence needs to be experimentally confirmed and characterized. 

Fig. 10.13. Schematic representation of the active-site access and product egress in tricorn and DP IV.

Beandstettee, H., Kim, J.-S., Geoll, M., and Huber, R. The crystal structure of the tricorn protease reveals a protein disassembly line. Nature 2001, 434, 466-469. 

Navigation inside a protease substrate selection and product exit in the tricorn protease from Thermoplasma acidophilum. 

Ponting, C. P. and Pallen, M. J. /5-Propeller repeats and a PDZ domain in the tricorn protease predicted self-compartmentalisa-tion and C-terminal polypeptide-binding strategies of substrate selection. FEMS Microbiol. Lett. 1999, 179, 447-451. 

Tamuea, N., Lottspeigh, F., Baumeistee, W., and Tamuea, T. The role of tricorn protease and its aminopeptidase-interacting factors in cellular protein degradation. Cell 1998,... 

R., Lottspeich, F., and Baumeister, W. Tricorn Protease - The Core of a Modular Proteolytic System. Science 1996a, 274, 1385-1389. 

The catalytic core is the part that ultimately cleaves the ubiquitinated protein into small peptides anywhere from 3 amino acids to 32 amino acids long. The peptides generated are probably further hydrolyzed to generate free amino acids by other proteases and amino peptidases. The proteases that break down the products of the proteasome action include but not limited to Thimet oligo peptidase, tricorn protease, and tripeptidyl protease... 

The alkaloids of Delphinium staphisagria have been reviewed. Delphidine has been shown to possess the structure (106) whilst delphirine (107) possesses the unusual C-1 hydroxy-group. Staphigine and staphirine are bisditerpenoid alkaloids which have been obtained " from D. staphisagria. Examination of D. tricorne afforded " a new alkaloid tricornine (108) which was shown to be 18-acetyl-... 

Alkaloids of Delphinium formosum.—Tanker and Ozden29 obtained an alkaloid fraction from the roots of this species, growing in Turkey, by treatment with ammonium hydroxide and benzene percolation. Thin-layer-chromatographic separation afforded six alkaloids. Two of these were identified as lycoctonine (39) and delsemine (see Alkaloids of D. tricorne , p. 228). 

Alkaloids of Delphinium tricorne Tricomine.—Examination of the alkaloid fraction of the whole-plant extract from D. tricorne Michaux revealed lycoctonine (39), Alkaloid A (36), Alkaloid B ( delsemine ), and a new base, tricomine (46), C27H43N08, m.pt. 187—189 °C.34 35... 

IN THE LATE afternoon, we go outside to learn about the natural world. My father wears a tricorn hat pressed firmly down on his wig and a trailing cloak that flattens the grass. We both have stout boots sent from Buckingham, and I carry a leather satchel and a jar with a cork lid in case we find anything of interest. His staff has a plain brass handle, and he waves it in front of him as if he needs to push aside the air. He walks too slowly for me, and I rein myself back to keep one step behind. 

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