N2-Tryptophyllysine

Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK(1), pK(2), and pK(R)) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the (1)L(a) transition dipole moment. Where quantum yield is low, isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp quantum yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished quantum yield in proteins as well. Thus tryptophan ground state isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes.

1. With carp myosin B ATPase, the acceleration effect was found at peptide concentration ranging between 1 nM and 1 mM with a maximum at 10 nM (30% acceleration) at the low myosin B concentration (0.2 mg/ml). At the high myosin B concentration (0.8 mg/ml) a maximum was observed at 1-10 mM (10% acceleration). 2. With rabbit myosin B ATPase, the acceleration (10%) was found only at a microM of Lys-Trp in the case of low myosin B concentration (0.2 mg/ml). Under the high concentration of rabbit myosin B, a maximum acceleration (150%) was found at 5 mM of the synthetic Lys-Trp. 3. Effect on superprecipitation was tested only at the high concentration of rabbit myosin B (0.8 mg/ml). The acceleration increased with increasing concentration of Lys-Trp up to 10 mM.

Effects of reaction pH and time on the antioxidant behaviors of Tyr, Trp, Cys, and their related peptides (Tyr-Gly, Tyr-Glu, Tyr-Lys, Trp-Gly, Trp-Glu, Trp-Lys, Cys-Gly and Cys-Gly) in ABTS assay were investigated. Results showed that all these amino acids and peptides displayed a biphasic kinetic pattern with a fast initial step and a slow secondary step. The initial reaction rates of Tyr, Trp and their related peptides were strongly dependent on pH, while those of Cys and Cys-containing peptides were unaffected by pH. They failed to reach equilibrium over the short incubation period of 6-10 min typically used in this assay. Longer incubation time was needed for most of the peptides to approach equilibrium at lower pH. The observed biphasic kinetic pattern as well as the high TEAC values for these amino acids and peptides, could be a result of combined antioxidant behaviors of themselves plus the generated reaction products.