Non-covalently bound complexes

In this scheme, electron transfer is proposed to take place in a non-covalently bound complex of the two proteins. The overall rate of reaction is then determined by the following parameters ... 

Fig. 8.5 Comparison between (a) the usual representations of catalysis and autocatalysis and (b) a more general version resulting from considering the cyclic architecture of reaction networks. The usual representation of enzyme catalysis deduced from Michaelis-Menten kinetics with two non-covalently bound complexes C S and C P fits the general description of a cycle by including the three states of the enzyme (free, bound to substrate, and bound to product). Genuine autocatalysis in its simplest version without covalent intermediate (up right) may be much more demanding than network autocatalysis because efficient autocatalysis requires that strong transient non-covalent interactions are present at the transition state whereas the reactant and product are stable in a monomer state. Moreover, the possibility that products or intermediates of downstream processes could be identical to intermediates of the metabolic cycle (M to M ) is statistically intaeased...

Computation times (in seconds on one Intel CoreDuo T9300 2.50 GHz CPU) for two non-covalently bound complexes with different quantum chemical methods... 

The non-covalently bound BPDEs to DNA formed initially appear to be intercalation complexes (1 6,52-55) Meehan et al. (1 6) report that the BPDE intercalates into DNA on a millisecond time scale while the BPDE alkylates DNA on a time scale of minutes. Most of the BPDE is hydrolyzed to tetrols (53-56). Geacintov et al. (5l ) have shown with linear dichroism spectral measurements that the disappearance of intercalated BPDE l(+) is directly proportional to the rate of appearance of covalent adducts. These results suggest that either there may be a competition between the physically non-covalently bound BPDE l(+) and an externally bound adduct or as suggested by the mechanism in the present paper, an intercalative covalent step followed by a relaxation of the DNA to yield an externally bound adduct. Their results for the BPDE i(-) exhibit both intercalative and externally bound adducts. The linear dichroism measurements do not distinguish between physically bound and covalent bound forms which are intercalative in nature. Hence the assumption that a superposition of internal and external sites occurs for this isomer. 

Vogtle has developed this approach further and employed a series of anionic templates to prepare rotaxanes (instead of the neutral template in the above reaction) [65-67]. In this approach a phenolate, thiophenolate or sulfonamide anion is non-covalently bound to the tetralactam macrocycle (46) forming a host-guest complex via hydrogen bonding (see Scheme 21). 

Fig. 2.2 ESI mass spectra obtained from the CPC spin column/ESI-MS screening assay of non-covalently bound protease-inhibitor complexes. Enzymatically active CMVP A144D/C87A/C138A/C161A A/as used in this experiment. (A) Reference ESI mass spectrum of impure inhibitor DFMK (MW 988.5 Da). (B) ESI mass spectrum of the spin column eluate of CMVP A144D/C87A/ C138A/C161A and DFMK, incubated at a...

Fig. 2.27 GPC spin column ESI-MS determination of MS EC50S. Plot of fraction of known ligand inhibitor non-covalently bound to a fixed amount of kinase protein ([P]o, 5 pM) as a function of initial ligand concentration [L]o. The MS EC50 corresponds to the free ligand concentration [L] when 50% of the initial protein concentration is tied up as protein-ligand complex. At 50% of the...

The five different coenzymes involved are associated with the enzyme components in different ways. Thiamine diphosphate is non-covalently bound to El, whereas lipoamide is covalently bound to a lysine residue of E2 and FAD is bound as a prosthetic group to E3. NAD" and coenzyme A, being soluble coenzymes, are only temporarily associated with the complex. 

Lanthanide complexes of mono- and tetra-amide /1-cyclodextrin derivatives of DOTA have been characterized [140]. The proton NMR spectra of the Eu3+ complexes in methanol-d, show that, while the tetra-amide complex occurs in solution exclusively as a C4-symmetry SAP structure, the mono-amide complex, with less than C4-symmetry, occurs predominantly as two SAP isomers (A/XXXX and Al8885), with the presence of a small amount of the twisted SAP isomer. Luminescence and relaxivity measurements confirm that the Eu3+, Tb3+ and Gd3+ complexes of the eight-coordinate mono-amide ligand possess one bound water molecule, while the tetra-amide complexes have q = 0. The relaxivity of the /LCD mono-amide Gd3+ complex is enhanced when non-covalently bound to a second Gd3+ complex bearing two phenyl moieties (MS-325, AngioMARK , EPIX/Mallinckrodt). 

There is evidence supporting a model that allows for the dissociation of both the active Ga-GTP and the non-covalently bound Py-heteromeric complex from the receptor-effector complex however, other models can also account for these data [55, 56]. Auxiliary proteins may regulate the potentiation of the GPCR-G protein effector complexes that generate second messengers or specific transmembrane proteins such as ion channels [39]. These processes are outlined schematically in Fig. 2. 

In the Golgi apparatus, the FVIII protein undergoes further post-translational modifications including complex glycosyla-tion, sulfation, and cleavage to two chains - the FVIII heavy chain (Al-al-A2-a2-B 90-200 kDa) and FVIII tight chain (a3-A3-C1-C2 80 kDa) (see Fig. 3.3). The heavy and tight chains remain non-covalently bound to each other in the presence of copper ions. Now, the FVIII molecule is ready to be secreted from the cell [18]. 

Carotenoids are non-covalently bound to complexes in the thylakoid membrane and are fundamentally important functional and structural components of the photosynthetic apparatus (Siefermann Harms, 1985, 1987 Peter and Thornber, 1991 Demmig Adams and Adams, 1992 Dreyfuss and Thomber, 1994a, 1994b Horton et al 1994 Grossman et al,... 

The absorption spectrum of the LH2 complex from Rps. acidophila is shown in Fig. 2. In the NIR two strong absorption peaks due to the Qy transition of BChl a are seen, one at -800 nm and the other at -860 nm (this complex is also called by the generic name B800-850). There are also two other prominent absorption bands due to BChl a, the Qx band at -590 nm and the Soret band at -380 nm. The three bands seen between 450 550 nm arise from the carotenoid, rhodopin-glucoside, which has 11 conjugated double bands. The BChls and the carotenoids are non-covalently bound to two low molecular weight, very... 

Kinetic studies demonstrated that the nuclease activity of Cu (phen)2 proceeds by an ordered mechanism the freely diffusing Cu (phen)2 is first reduced to the Cu complex Cu (phen)2 which binds reversibly to DNA. This non-covalently bound Cu complex is then oxidized by H2O2 to generate the reactive species responsible for DNA strand scission (19). The association constant for DNA binding of Cu (phen)2 was determined to be 4.7 x 10 (DNA base pairs) (13). However, Cu (phen)2 also binds to DNA, but the direct reduction of the complex Cu (phen)2---DNA by 0 is very slow and can be neglected (25). 

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