Metastable decomposition at the peptide C-terminus: Possible use in protein identification.

RATIONALE: The b n-1 ion of a peptide, as well as a [b n-1 + 18] ion, can be observed not only as normal product ions, but also as prominent metastable ions in a reflectron-embedded matrix-assisted laser desorption ionization time-of-flight spectrometer. The m/z values for the peaks are slightly shifted compared with the ordinary product ions and appear as relatively broad peaks, which permits them to be discriminated from other ions. METHODS: A standard protein mixture and gel-derived proteins digested with LysN protease, which cleaves peptide linkages in proteins at the N-terminal side of Lys residues, were examined. The collected data were used for protein identification using in-house software, iD-plus (http://coco.protein.osaka-u.ac.jp/id-plus/), which was developed for searching for proteins in the peptide database, based on enzyme specificity (N-terminal Lys in this study), peptide masses and C-terminal amino acids. RESULTS: The b n-1 as well as [b n-1 + 18] ions were observed as broad ion peaks for all of the peptides (86 peptides) examined in this study. In silico calculations using the database of LysN digested peptides (11 969 470), created from 553 941 protein sequences (SwissProt: 2017_03), indicate that the use of no less than four peptides permits a protein to be identified without the need of any probability-based scoring. CONCLUSIONS: The preference for b n-1 ion formation is probably due to the higher propensity of the C-terminal peptide bond to be cleaved than other internal bonds. The fact that such C-terminal fragmentation takes place for most of the peptides examined suggests that the use of an N-terminal specific enzyme would allow the C-terminal amino acids to be more reliably read out than other internal sequences, information that could be efficiently used for protein identification.

Idoxifene and estradiol enhance antiapoptotic activity through estrogen receptor-beta in cultured rat hepatocytes.

Oxidative stress plays a causative role in the development of hepatic fibrosis and apoptosis. Estradiol (E2) is an antioxidant, and idoxifene is a tissue-specific selective estrogen-receptor modulator. We have previously demonstrated that E2 inhibits hepatic fibrosis in rat models of hepatic fibrosis and that the actions of E2 are mediated through estrogen receptors (ERs). This study reports on the antiapoptotic role of idoxifene and E2, and the functions of ER subtypes ER-alpha and ER-beta in hepatocytes undergoing oxidative stress. Lipid peroxidation was induced in cultured rat hepatocytes with ferric nitrilotriacetate solution with idoxifene or E2. Oxidative stress-induced early apoptosis was linked to its ability to inhibit not only the expression of Bcl-2 and Bcl-XL but the production of antioxidant enzymes as well and to stimulate Bad expression. Hepatocytes possessed functional ER-beta, but not ER-alpha, to respond directly to idoxifene and E2. Idoxifene and E2 suppressed oxidative stress-induced reactive oxygen species generation and lipid peroxidation, and their antiapoptotic effects on the activation of activator protein-1 and nuclear factor-kappaB, the loss of antioxidant enzyme activity, and Bcl-2 family protein expression in early apoptotic hepatocytes were blocked by the pure ER antagonist ICI 182,780. Our results indicate that idoxifene and E2 could enhance antiapoptotic activity through ER-beta during oxidative damage in hepatocytes.

A relative high dose of vitamin E does not attenuate unweighting-induced oxidative stress and ubiquitination in rat skeletal muscle.

We previously reported that intragastric administration of cysteine could be beneficial to prevent unweighting-induced ubiquitination and degradation of muscle protein in association with redox regulation [Ikemoto et al., Biol. Chem., 383 (2002), 715-721]. In this study, we investigated whether vitamin E, another potent antioxidative nutrient, also had beneficial effects on the muscle protein catabolism. However, daily intragastric supplementation of 1.5 or 15 mg/rat of alpha-tocopherol did not prevent weight loss of hindlimb skeletal muscle in tail-suspended rats. To elucidate the reason for the non-effectiveness of vitamin E, we further examined concentrations of oxidative stress markers, ubiquitination of muscle proteins and fragmentation of myosin heavy chain in gastrocnemius muscle of rats daily treated with 15 mg of alpha-tocopherol. Unexpectedly, vitamin E increased concentrations of glutathione disulfide and thiobarbituric acid-reactive substance and decreased glutathione level in the muscle, compared with those of vehicle treatment, indicating that vitamin E enhanced unweighting-induced oxidative stress in skeletal muscle. The vitamin E supplementation did not suppress the ubiquitination of muscle proteins and fragmentation of myosin heavy chain caused by tail-suspension. Our results suggest that supplementation of a relative high dose of vitamin E could not inhibit ubiquitin-dependent degradation of muscle protein in tail-suspended rats possibly due to its prooxidant action.