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The experimental analysis of 6,8-dimethylisoxanthopterin (6,8DMI) showed that absorbance and fluorescence emission spectra of 6,8DMI shift to lower energies as the pH is increased yielding pKa values of 8.3 and 8.5 respectively. The quantum mechanical calculations on the neutral and deprotonated forms of 6,8DMI confirm the observed spectral changes.

Research reveals that the endoplasm reticulum glycoprotein gp96/GRP94 oligomerizes into larger multimeric complexes with size ranging from dimers to octamers and higher. The oligomerization occurs with or without the dimerization domain participation, and in the peptide uptake by gp96, the dimerization domain plays only a minor role.

An evaluation of the asymmetry and conformational dynamics of human blood clotting enzyme VIIa (VIIa) and the complex it forms with a soluble truncation mutant of human tissue factor (sTF) was undertaken using ultracentrifugation and fluorescence anisotropy decay measurements. The results clearly demonstrate that VIIa and sTF are both highly asymmetric. Moreover, the binding of sTF to VIIa induces a conformational change in VIIa, leading to the loss of segmental flexibility of VIIa in the domain containing the active site.

A search was conducted for tryptophan analogs that can be used for spectral enhancement of proteins, resulting in the identification of 5-hydroxytryptophan (5-OHTrp) as a likely candidate for the generation of spectrally-enhanced proteins (SEPs). A tryptophan-requiring Escherichia coli auxotroph was used to replace the three tryptophan residues in the lambda cI repressor with 5-OHTrp. Fluorescence and absorbance analyses showed that the substituted protein is spectrally enhanced. In addition, the SEP was functionally indistinguishable from the wild-type protein.

The fluorescence properties of (tryptophan2)oxytocin were studied using intensity decay parameters and 1H NMR results. It was shown that results of fluorescence studies using a tryptophan analogue are compatible with the rotamer model of (Tyr2)oxytocin. The X2 conformers of the tryptophan analogue do not significantly affect fluorescence decay kinetics and three decay constants can be found in the three X1 rotamers of tryptophan.

A system with two fluorescent species and two depolarizing processes that experimentally validates the general scheme of the two of nine possible kinetic models is described. Model one is confirmed using a binary solution of indole and beta-cyclodextrin and model two was verified using a binary solution of melatonin and rat F102W parvalbumin.

Lipoprotein(a) [Lp(a)] is a low-density lipoprotein complex consisting of apolipoprotein(a) [apo(a)] disulfide-linked to apolipoprotein B-100. Lp(a) has been implicated in atherogenesis and thrombosis through the lysine binding site (LBS) affinity of its kringle domains. We have examined the oxidative effect of 2,2′-azobis-(amidinopropane) HCI (AAPH), a mild hydrophilic free radical initiator, upon the ability of Lp(a) and recombinant apo(a), r-apo(a), to bind through their LBS domains. AAPH treatment caused a time-dependent decrease in the number of functional Lp(a) or r-apo(a) molecules capable of binding to fibrin or lysine-Sepharose and in the intrinsic protein fluorescence of both Lp(a) and r-apo(a). The presence of a lysine analogue during the reaction prevented the loss of lysine binding and provided a partial protection from the loss of tryptophan fluorescence. The partial protection of fluorescence by lysine analogues was observed in other kringle-containing proteins, but not in proteins lacking kringles. No significant aggregation, fragmentation, or change in conformation of Lp(a) or r-apo(a) was observed as assessed by native or SDS-PAGE, light scattering, retention of antigenicity, and protein fluorescence emission spectra. Our results suggest that AAPH destroys amino acids in the kringles of apo(a) that are essential for lysine binding, including one or more tryptophan residues. The present study, therefore, raises the possibility that the biological roles of Lp(a) may be mediated by its state of oxidation, especially in light of our previous study showing that the reductive properties of sulfhydryl-containing compounds increase the LBS affinity of Lp(a) for fibrin. [ABSTRACT FROM AUTHOR]