Tryptophan stability

Water-soluble globular proteins usually have an interior composed almost entirely of non polar, hydrophobic amino acids such as phenylalanine, tryptophan, valine and leucine witl polar and charged amino acids such as lysine and arginine located on the surface of thi molecule. This packing of hydrophobic residues is a consequence of the hydrophobic effeci which is the most important factor that contributes to protein stability. The molecula basis for the hydrophobic effect continues to be the subject of some debate but is general considered to be entropic in origin. Moreover, it is the entropy change of the solvent that i... 

The best procedures for 3-vinylation or 3-arylation of the indole ring involve palladium intermediates. Vinylations can be done by Heck reactions starting with 3-halo or 3-sulfonyloxyindoles. Under the standard conditions the active catalyst is a Pd(0) species which reacts with the indole by oxidative addition. A major con.sideration is the stability of the 3-halo or 3-sulfonyloxyindoles and usually an EW substituent is required on nitrogen. The range of alkenes which have been used successfully is quite broad and includes examples with both ER and EW substituents. Examples are given in Table 11.3. An alkene which has received special attention is methyl a-acetamidoacrylate which is useful for introduction of the tryptophan side-chain. This reaction will be discussed further in Chapter 13. 

Inactivation and Removal of Viruses. In developing methods of plasma fractionation, the possibiHty of transmitting infection from human vimses present in the starting plasma pool has been recognized (4,5). Consequentiy, studies of product stabiHty encompass investigation of heat treatment of products in both solution (100) and dried (101) states to estabHsh vimcidal procedures that could be appHed to the final product. Salts of fatty acid anions, such as sodium caprylate [1984-06-17, and the acetyl derivative of the amino acid tryptophan, sodium acetyl-tryptophanate [87-32-17, are capable of stabilizing albumin solutions to 60°C for 10 hours (100) this procedure prevents the transmission of viral hepatitis (102,103). The degree of protein stabilization obtained (104) and the safety of the product in clinical practice have been confirmed (105,106). The procedure has also been shown to inactivate the human immunodeficiency vims (HIV) (107). 

No 1 -hydroxytryptamine or -tryptophan alkaloid that lacks a stabilizing group on the indole nucleus has been reported yet. However, isolation of37,38a, 38b, HUN-7293 (293) (96MI69), and apicidin (301) (96TL8077) offers indirect evidence for the existence of 1-hydroxytryptamines and/or 1-hydroxytryptophans in living organisms. We believe their isolation will be reported in the near future. 

The intramolecular distances measured at room temperature with the AEDANS FITC pair were similar in the Ca2Ei and E2V states [297]. Ca and lanthanides are expected to stabilize the Ej conformation of the Ca -ATPase, since they induce a similar crystal form of Ca -ATPase [119,157] and have similar effects on the tryptophan fluorescence [151] and on the trypsin sensitivity of Ca -ATPase [119,120]. It is also likely that the vanadate-stabilized E2V state is similar to the p2 P state stabilized by Pi [418]. Therefore the absence of significant difference in the resonance energy transfer distances between the two states implies that the structural differences between the two conformations at sites recorded by currently available probes, fall within the considerable error of resonance energy transfer measurements. Even if these distances would vary by as much as 5 A the difference between the two conformations could not be established reliably. 

Various spectroscopic approaches applied to the 510 nm transition indicate an unusual environment for the redshifted lutein (Figures 7.5 and 7.7a). Interaction with the Chi a603 could force lutein 2 molecule to adopt a twisted configuration. In addition, strong interaction with a number of aromatic residues, in particular tryptophan and phenylalanine, which possess relatively large surface areas, could further promote this distortion. It is reasonable to assume that the energy required to produce this distortion comes from the forces involved in the stabilization of LHCII trimers. 

L. Zheng and J.D. Brennan, Measurement of intrinsic fluorescence to probe the conformational flexibility and thermodynamic stability of a single tryptophan protein entrapped in a sol-gel derived glass matrix. Analyst 123, 1735-1744 (1998). 

The instability of these chiral monolayers may be a reflection of the relative stabilities of their bulk crystalline forms. When deposited on a clean water surface at 25°C, neither the racemic nor enantiomeric crystals of the tryptophan, tyrosine, or alanine methyl ester surfactants generate a detectable surface pressure, indicating that the most energetically favorable situation for the interfacial/crystal system is one in which the internal energy of the bulk crystal is lower than that of the film at the air-water interface. Only the racemic form of JV-stearoylserine methyl ester has a detectable equilibrium spreading pressure (2.6 0.3dyncm 1). Conversely, neither of its enantiomeric forms will spread spontaneously from the crystal at this temperature. 

The characteristics that discourage the use of RPLC for preparative isolation of bioactive proteins favor its use as an analytical tool for studying protein conformation. Chromatographic profiles can provide information on conformational stability of a protein and the kinetics of folding and unfolding processes. Information about solvent exposure of certain amino acid residues (e.g., tryptophan) as a function of the folding state can be obtained by on-line spectral analysis using diode array UV-vis detection or fluorescence detection. 

The third class of host defense peptides, the extended peptide class, is defined by the relative absence of a defined secondary structure. These peptides normally contain high proportions of amino acids such as histidine, tryptophan, or proline and tend to adopt an overall extended conformation upon interaction with hydrophobic environments. Examples of peptides belonging to the extended class include indolicidin, a bovine neutrophil peptide, and the porcine peptide fragment, tritpticin. These structures are stabilized by hydrogen bonding and van der Waals forces as a result of contact with lipids in contrast to the intramolecular stabilization forces found in the former peptide classes. 

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