双酶电极法测定L-苯丙氨酸的研究

本文以Clark氧电极为基础 ,把水杨酸羟化酶和苯丙氨酸脱氢酶同时固定在氧电极的表面 ,制成了双酶生物传感器。在磷酸缓冲液中 ,水杨酸浓度为 0 .5mmol/L ,烟酰胺腺嘌呤二核甘酸 (NAD+)的浓度为 1 .0mmol/L ,其响应电流的变化对应反池中L 苯丙氨酸的浓度在 0～ 0 .1 5mmol/L之内有良好的线性范围。

Effects and mechanisms of L-phenylalanine on growth of Microcystis aeruginosa

The effects and possible mechanisms of action of L- phenylalanine on the growth of Microcystis aeruginosa cells were explored by cell counting and flow cytometry assays. L- phenylalanine promoted the growth of Microcystis aeruginosa at concentrations between 0.078 and 0. 312 μg/mL, but inhibited growth at concentrations between 0. 625 and 20μg/mL in 24 h exposure. The dose-effect and time-course relationships between exposure to L-phenylalanine and growth inhibition of Microcystis aeruginosa were observed. The IC50 value of L-phenylalanine for growth inhibition of Microcystis aeruginosa was 6. 2 μg/mL （95% confidence interval was 0. 005 to 16. 76 μg/mL）. The membrane integrity of the cells showed significant variations after 24 h exposure to L-phenylalanine. Meanwhile, no effects on esterase activity of the cells were observed until after 48 h exposure to L-phenylalanine. In conclusion, L-phenylalanine has hormesis effects and algae control effects on Microcystis aeruginosa. The latter is closely related to alterations or disorders in the cell membrane and with variation of esterase activity in the cells.

Inhibitory Effect of Ferulic Acid on Oxidation of L-DOPA Catalyzed by Mushroom Tyrosinase

The inhibitory effect of ferulic acid on the diphenolase activity of mushroom tyrosinase and the kinetic behavior were studied with L-3,4-dihydroxyphenylalanine （L-DOPA） as substrate. The inhibitor concentration leading to 50% relative activity lost （IC50） was estimated to be 0.15 mmol·L^-1. The inhibition mechanism obtained from Lineweaver-Burk plots shows that ferulic acid is a competitive inhibitor and the inhibition of tyrosinase by ferulic acid is a reversible reaction. The equilibrium constant for ferulic acid binding with the tyrosinase was determined to be 0.25 mmol·L^-1 for diphenolase. Keywords tyrosinase, ferulic acid, kinetics, inhibition, L-DOPA, diphenolase

Synthesis of Protected Tetrapeptide, N-o-Ns-N(Me)-Val-N(Me)-Val-N(Me)-Val-N(Me)-Phe-O^tBu

The protected tetrapeptide, N-o-Ns-N （ Me ） -Val-N （ Me ） -Val-N （ Me ） -Val- N （ Me ） -Phe- OtBu, was prepared from L-valine and L-phenylalanine. Ted-butyl acetate and HClO4 were used to protect carbonyl group, o-nitrobenzenesulfonyl chloride and triethyl amine were used to protect amino group, and N-alkylation was finished with iodomethane. Then the protected amino acid was turned into acid chloride which was taken as coupling reagent. After 14 steps, such as protection, alkylation, deprotection and coupling, the protected tetrapeptide was obtained with a yield of 26.9%. The structures of intermediates and target compound were identified with NMR spectra and high resolution mass spectra.

Enzymatic Synthesis of Halogen Derivatives of Aromatic Amino Acids Labeled with Hydrogen Isotopes

The isotopomers of halogenated amino acids （2＇-F-L-phenylalanine, 3＇-F- and 3＇-Cl-L-tyrosine, as well as 5＇-F-, 5＇-Br-and 6＇-F-L-tryptophan） specifically labeled with deuterium at α- and 13-carbon atom of the side chain were synthesized by enzymatic catalyzed H/D exchange in fully deuteriated incubation medium. The extent and site of deuterium incorporation were confirmed by ^1H NMR （proton nuclear magnetic resonance） spectra.

Improved synthesis of rupintrivir

An improved synthesis of rupintrivir (AG7088) was accomplished using three amino acids (L-glutamic acid, D-4-fluorophenylalanine, and L-valine) as the building blocks. The key fragment ketomethylene dipeptide isostere was constructed with the valine derivative and phenylpropionic acid derivative, followed by coupling with a lactam derivative and an isoxazole acid chloride to provide AG7088 totally in eight steps.