Studies on l-Glutamate Oxidase with Strict Substrate Specificity from Streptomyces sp.

l-glutamate oxidase (LGOX) from Streptomyces sp. is a heterohexameric flavin enzyme that catalyzes the oxidative deamination of l-glutamate to form α-ketoglutarate with ammonia and hydrogen peroxide. LGOX shows strict substrate specificity for l-Glu. In addition, it is highly thermostable and pH stable. Because of these properties, LGOX is currently used as a biosensor for the trace determination of l-Glu in the food industry and clinical laboratories. The full-length cDNA is 2103 bp and is encoded by a single polypeptide chain consisting of 701 residues including subunits α-γ-β. The LGOX gene was heterologously expressed in Escherichia coli JM109. The LGOX precursor expressed in E. coli is a homodimer with weak enzymatic activity and becomes a heterohexamer upon activation by protease treatment. X-ray crystallography and docking studies of purified recombinant LGOX suggest that the Arg305 residue is a key residue for substrate recognition. Mutant analysis showed that Arg305 is essential for substrate recognition, as the activity toward l-Glu was greatly reduced and substrate specificity was changed in some enzymes. The functional analysis of R305E-LGOX, which is an l-Arg oxidase, revealed that R305E-LGOX can be used as a enzyme biosensor for l-Arg

Frustrated quantum-spin system on a triangle coupled with ege_g lattice vibrations - Correspondence to Longuet-Higgins et al.'s Jahn-Teller model -

We investigate the quantum three spin model $({\bf S_1},{\bf S_2},{\bf S_3})$ of spin$=1/2$ on a triangle, in which spins are coupled with lattice-vibrational modes through the exchange interaction depending on distances between spin sites. The present model corresponds to the dynamic Jahn-Teller system $E_g\otimes e_g$ proposed by Longuet-Higgins {\it et al.}, Proc.R.Soc.A.{\bf 244},1(1958). This correspondence is revealed by using the transformation to Nakamura-Bishop's bases proposed in Phys.Rev.Lett.{\bf 54},861(1985). Furthermore, we elucidate the relationship between the behavior of a chiral order parameter ${\hat \chi}={\bf S_1\cdot(S_2\times S_3)}$ and that of the electronic orbital angular momentum ${\hat \ell_z}$ in $E_g\otimes e_g$ vibronic model: The regular oscillatory behavior of the expectation value $$for vibronic structures with increasing energy can also be found in that of$$. The increase of the additional anharmonicity(chaoticity) is found to yield a rapidly decaying irregular oscillation of $$

Dynamic regulation of Ero1 and peroxiredoxin 4 localization in the secretory pathway

In the early secretory compartment (ESC), a network of chaper- ones and enzymes assists oxidative folding of nascent proteins. Ero1 flavoproteins oxidize protein disulfide isomerase (PDI), gen- erating H2O2 as a byproduct. Peroxiredoxin 4 (Prx4) can utilize luminal H2O2 to oxidize PDI, thus favoring oxidative folding while limiting oxidative stress. Interestingly, neither ER oxidase contains known ER retention signal(s), raising the question of how cells pre- vent their secretion. Here we show that the two proteins share sim- ilar intracellular localization mechanisms. Their secretion is pre- vented by sequential interactions with PDI and ERp44, two resident proteins of the ESC-bearing KDEL-like motifs. PDI binds preferentially Ero1 , whereas ERp44 equally retains Ero1 and Prx4. The different binding properties of Ero1 and Prx4 increase the robustness of ER redox homeostasis