Multimer trimer

The first intermediate can associate to form the dimer with an equilibrium constant,, for final protein concentrations greater than 10 /xM. The dimer equilibrium constant,, was 1.8 0.2 /xM" as calculated from the QLS data and 1.3 0.1 /xM using the HPLC data. The largest multimer, trimer, was formed from the association of a dimer and a monomer with an equilibrium constant, Kj. For this association reaction, the equilibrium constant, Kj, was 0.53 0.12 gM and 0.42 0.11 for QLS and HPLC analyses, respectively. The equilibrium constants for dimer and trimer formation are comparable using these two analytical techniques. 

Let us consider a system of N molecules with one proton donor and one acceptor site (-0-H groups), which self-associate forming bonds. However, the first dimer bond, now, is weaker than any subsequent bond in a multimer (trimer, tetramer, etc.) complex. In fact, it is not important for the enumeration of bonds whether the dimer bond is weaker or stronger than the others it suffices for it to be distinguishable. 

Type X collagen has a single al chain, which contains a short collagenous domain of 460 residues, flanked by an N-terminal NC domain of 37 residues and C-terminal NC domain of 161 residues." Its protomer is a homotrimer. The C-terminal NC domain is responsible for trimerization and multimer formation, which is based on experiments with recombinant domains." The crystal structure of type X collagen trimerization domain is similar to that of type VIII collagen (see also Section 5.16.6.5). 

M. Davies (Aberystwyth) The use of the term polymer for the associated molecules formed from stable monomers by hydrogen bonding, etc, seems objectionable, and it is suggested that the equivalent, self-explanatory term multimer be used in these circumstances. Thus the reversible association of molecules leading to a complex which can be completely dissociated by dilution at the working temperature would be referred to as the formation of a multimer. This leaves unchanged the use of dimer , trimer , etc. for particular species in contexts where it is clear that only weak reversible agglomeration is involved. 

The other procedure described for the generation of multivalent globotriaose dendrimers for protection against VTl or VT2 cytotoxicity in vivo is based on carbosilane multimers (183). These multimers are more systematic expansions of trimeric structures that are based on multiples of the tetrameric carbosilane (184). In these studies, coupling the two terminal silicon residues of a linear carbosilane trimer ( super twig ) to either... 

Hi er order terms can be defined as well, but what little experience is availabk has taught us that they are generally smaller by at least an order of magnitude. Still, they can be important if we look at specific effects such as the non-pairwise additive components to the interaction oiergy in Van der Waals trimers or multimers (cf. the last part of this section). In the second order sununation over excited states (18) we can separate three different contrilmtions ... 

The second additivity problem concerns the question whether the interaction potential in Van der Waals trimers or multimers (or molecular solids or liquids) is a sum of pairwise intermolecular (A—B) potentials. This question can be considered for each component of the interaction energy. The (first order) electro-... 

Generally, specific proteins can bind to each other In the body to form dimers (duplex structures), trimers, tetramers, or even larger multiples. These subunit proteins may be of identical or different structure. The different proteins in these mullimeric structures arc bound to each other by hydrogen bonds and other weak interactions. Ihese multimers often perform physiological functions that cannot be carried out by the individual separated proteins. 

Equation ix or x can readily be solved for various [H ] and for TOTFe(][H) = 10" M, especially if one assumes that the dimer and the trimer can be neglected in this dilute solution. Figure 6.5a gives the answer. The multim ric species are present at less than 10 M and can be neglected. The figure illustrates that Fe is essentially a four-protic acid. 

Figure 1 Refolding and aggregation model for bovine carbonic anhydrase B (CAB). When denatured CAB in 5 M GuHCl is rapidly diluted to refolding conditions, the unfolded protein, U, forms the first intermediate, 1 This intermediate continues to refold to the second intermediate, L, which proceeds to fold to the native protein, N. If the unfolded protein is diluted to aggregating conditions, the first intermediate will associate to form multimers. The dimer, D, and trimer, T, species can further associate, resulting in the formation of large aggregates. (Reproduced from ref. 1. Copyright 1990 American Chemical Society.)...

Tn the absence of other more specific interactions, hydrogen bonding leads to an aggregation of water into clusters and in liquid alcohols and diols to the formation of associated species, which are thought to include dimers, trimers, and higher multimers. 

The values of the enthalpy obtained do not depend on the model chosen for the dimer, as shown by Lussan (19) in a comprehensive summary of the possible theoretical treatments of the NMR data. Lussan demonstrates the form of the equilibrium constant calculation in the case of (1) monomer-dimer (open or cyclic), (2) monomer-cyclic trimer, and (3) monomer-higher acyclic multimers in the two cases of (3a) all K s equal and (3b) ki for monomer-dimer equilibrium unique, k s for higher multimers all equal. He then takes the experimental curves for a number of alcohols in carbon tetrachloride and achieves a reasonable fit to the data up to 0.6 mole fraction by using one or the other of the theoretical relationships. In some cases two sets of theoretical points are plotted on the same graph as the experimental data both are a good fit in the low concentration region, up to 0.1 mole fraction. Above this concentration one or the other of the theoretical curves is much closer to the experimental curve. Lussan implies that hypothesis 3b may be a more accurate fit to the data in the more concentrated solutions. Methanol, ethanol, 2-methyl-2-propanol (tert-butyl alcohol) and 2,2,4-trimethyl-3-pentanol follow the curve for equilibrium 3a, while 2,2,4,4-tetramethyl-3-pentanol fits the monomer-dimer data. Lussan points out that the behavior of the latter alcohol fits in with that of two similar heavily substituted tertiary alcohols which have been found by infrared methods to form only dimers. 

Ibbitson and Moore (13) conclude that the maximum in the curve of polarization vs. concentration for ethanol in carbon tetrachloride is caused by linear multimers, and the subsequent fall in polarization is caused by an increasing amount of cyclic multimer (Figure 1). The concentration at which the maximum occurs coincides with that at which the 3350-cm.-1 band first appears in the infrared spectrum, so they have suggested that this band arises from cyclic multimers. They have fitted their data to a system containing linear dimer and trimer and cyclic tetramer only and have evaluated association constants for these species. 

Assuming that the minimum in the curve of /z2 vs. concentration is caused by the presence of cyclic multimers, Huyskens calculated the relative numbers of molecules, r, involved in the cyclic structures from the dipole moment curves. He then obtained values of the monomer concentrations, ci, from infrared data and compared qualitatively the variation with concentration of r and appropriate functions of c for the case of two-, three-, and four-membered cyclic multimers. Best agreement was obtained with the cyclic trimer curve in most cases although the importance of bigger rings seemed to increase with the chain length of the alcohol. 

The large positive saturation in dilute solutions is caused by the high concentration of dimers, in which the dielectric saturation is shown by Piekara to lead to the largest increase in dipole moment. From curves which show the variation in mole fraction of each multimer with concentration it appears that in 1-hexanol there are 65 mole % pentamers, 25 mole % tetramers, and 10 mole % trimers approximately in the pure liquid. Malecki has also calculated that 60% of dimers and 37% of trimers are cyclic, the tetramers and pentamers revealing no cyclic structures. The forms of the curves showing variations in concentration of monomer and the various multimers with total concentration of hexanol are similar to... 

Huyskens (10, 11, 12) I nf rared-dielectric measurements Some cyclic multimers, predominantly trimers... 

There is still no certain information obtainable from infrared and NMR measurements on cyclic dimers or multimers. The dimer band may arise from a cyclic species involving nonlinear hydrogen bonds, and one might expect that if a cyclic trimer exists, the OH stretching frequency would be similar to and slightly lower than that of a cyclic dimer. This would account for the broadening of the dimer band in pentamethylethanol at high concentrations. 

The mass analysis of an effusive beam of metal particles from a Knudsen cell allows us to calculate the equilibrium constants for the formation of dimers, trimers, etc. Performing similar studies over a wide range of temperatures then allows us to obtain the complete set of thermodynamic quantities free energy, enthalpy, and entropy of formation. Unfortunately, the multimer concentrations are typically so small that this technique is limited to an analysis of the thermodynamics of only dimers except in favorable cases. Nevertheless, these studies provide a convenient check for spectroscopic measurements of bond energies. 

The properties of the crystalline enzyme from calf liver have been studied by Levine et al. (1969). Despite several recrystallizations the enzyme preparations showed up to three minor components on analytical ultracentrifugation, sucrose density gradient centrifugation, or polyacrylamide gel electrophoresis. This was not due to the presence of impurities, but rather to the occurence of multimers of the enzyme, i.e., monomer, dimer, trimer, and tetramer. Evidence to this effect was obtained from the close correspondence between protein content and enzyme activity in the fractions isolated by density gradient centrifugation and gel electrophoresis. Furthermore, the separated fractions slowly redistributed to yield analytical patterns similar to that of the native enzyme, indicating that interconversion between the various molecular species was taking place. 

Pereira AS, Tavares P, Lloyd SG, Danger D, Edmondson DE, Theil EC, Huynh BH. 1997. Rapid and parallel formation of Fe multimers, including a trimer, during H-type subunit ferritin mineralization. Biochemistry 36 7917-7927. 

Enoate reductase. Enoate reductase isolated from Clostridium tyrobutyricum catalyses the NADH or methylviologen-dependent reduction of the a,p carbon-carbon double bond of non-activated 2-enoates and in a reversible way that of 2-enals. The enzyme appears to be a multimer of identical subunits. The total molecular mass is 940 kDa ( 73 kDa per subunit). Sedimentation equilibrium experiments, molecular mass data, and electron microscopy indicate that the native enzyme is composed of a tetramer of trimers. Each enzyme subunit contains one FAD, 0.6 FMN and one [4Fe-4S] cluster. 

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