Hasil untuk "physics.soc-ph"

G. Monin, P. Sellier

O. Petroff, J. Prichard, K. Behar et al.

R. Harter

F. Mould, E. Ørskov, S. Mann

J. Etherington, R. Wright, V. Baligar et al.

M. Chuan, G. Shu, J. C. Liu

R. Martínez‐Zaguilán, E. Seftor, R. E. Seftor et al.

M. Lemmon, K. Ferguson, J. Schlessinger

With the identification of two distinct classes of high affinity, physiologically relevant, ligands for PH domains, it appears reasonable to assume that additional specific high affinity ligands for other PH domains will be identified in the future. It is not clear, however, whether each of the 90 proposed PH domains will have its own specific ligand. Possible candidates for specific PH domain ligands include various inositol polyphosphates, phosphorylated membrane components, as well as specific protein sequences containing phosphorylated tyrosine, serine, threonine, or histidine residues. It appears unlikely that the low affinity interactions of phosphoinositides described for several PH domains are physiologically relevant. It is difficult to imagine why such a large and diverse family of PH domains (with just 10-15% sequence identity) would exist in order to bind with a similar low affinity to PtdInsP2-containing membranes. Rather, we suggest that these interactions represent limited binding to noncognate ligands - the physiologically relevant ligands have yet to be identified. It is likely that many, if not all, PH domains have their own high affinity, cell membrane-associated, ligands and operate according to the paradigms described for the PH domains of PLCδ1 and Shc (Figure 2Figure 2A and Figure 2Figure 2B). The structural homology between PH domains might reflect a particularly stable protein scaffold of β sheets that can present variable ligand-binding loops in a manner analogous to that seen in the immunoglobulin superfamily.

Feng Xu

The electronic absorption spectrum, susceptibility to fluoride inhibition, redox potential, and substrate turnover of several fungal laccases have been explored as a function of pH. The laccases showed a single spectrally detectable acid-base transition at pH 6-9 and a fluoride inhibition that diminished by increased pH (indicating a competition with hydroxide inhibition). Relatively small changes in the redox potentials (≤0.1 V) of laccase were observed over the pH 2.7-11. Under the catalysis of laccase, the apparent oxidation rates (kcat and kcat/Km) of two nonphenolic substrates, potassium ferrocyanide and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid),decreased monotonically as the pH increased. In contrast, the apparent oxidation rates (kcat and kcat/Km) of three 2,6-dimethoxyphenols (whose pKa values range from 7.0 to 8.7) exhibited bell-shaped pH profiles whose maxima were distinct for each laccase but independent of the substrate. By correlating these pH dependences, it is proposed that the balance of two opposing effects, one generated by the redox potential difference between a reducing substrate and the type 1 copper of laccase (which correlates to the electron transfer rate and is favored for a phenolic substrate by higher pH) and another generated by the binding of a hydroxide anion to the type 2/type 3 coppers of laccase (which inhibits the activity at higher pH), contributes to the pH activity profile of the fungal laccases.

C. Appel, L. Ma

Ru Liu, Si-ming Zhao, Shanbai Xiong et al.

M. Hrubý, Č. Koňák, K. Ulbrich

J. Horiuchi, T. Shimizu, K. Tada et al.

P. Sun, Jinyuan Zhou, Weiyun Sun et al.

Jianming Xu, Caixian Tang, Zuliang Chen

L. Gerweck, Shashirekha Vijayappa, S. Kozin

M. Sohail, R. Siddiqi, Aqeel Ahmad et al.

R. Wahab, S. Ansari, Young-Soon Kim et al.

N. Maalouf, M. Cameron, O. Moe et al.

Warisara Lertpaitoonpan, S. Ong, T. Moorman