Hydrolytic properties of a thermostable α-L-arabinofuranosidase from Caldicellulosiruptor saccharolyticus.

AIMS: To characterize of a thermostable recombinant α-L-arabinofuranosidase from Caldicellulosiruptor saccharolyticus for the hydrolysis of arabino-oligosaccharides to l-arabinose. METHODS AND RESULTS: A recombinant α-L-arabinofuranosidase from C. saccharolyticus was purified by heat treatment and Hi-Trap anion exchange chromatography with a specific activity of 28.2 U mg(-1). The native enzyme was a 58-kDa octamer with a molecular mass of 460 kDa, as measured by gel filtration. The catalytic residues and consensus sequences of the glycoside hydrolase 51 family of α-L-arabinofuranosidases were completely conserved in α-L-arabinofuranosidase from C. saccharolyticus. The maximum enzyme activity was observed at pH 5.5 and 80°C with a half-life of 49 h at 75°C. Among aryl-glycoside substrates, the enzyme displayed activity only for p-nitrophenyl-α-L-arabinofuranoside [maximum k(cat)/K(m) of 220 m(mol l(-1))(-1) s(-1)] and p-nitrophenyl-α-L-arabinopyranoside. This substrate specificity differs from those of other α-L-arabinofuranosidases. In a 1 mmol l(-1) solution of each sugar, arabino-oligosaccharides with 2-5 monomer units were completely hydrolysed to L-arabinose within 13 h in the presence of 30 U ml(-1) of enzyme at 75°C. CONCLUSIONS: The novel substrate specificity and hydrolytic properties for arabino-oligosaccharides of α-L-arabinofuranosidase from C. saccharolyticus demonstrate the potential in the commercial production of L-arabinose in concert with endoarabinanase and/or xylanase. SIGNIFICANCE AND IMPACT OF THE STUDY: The findings of this work contribute to the knowledge of hydrolytic properties for arabino-oligosaccharides performed by thermostable α-L-arabinofuranosidase.

Precision measurement of cosmic-Ray antiproton spectrum

The energy spectrum of cosmic-ray antiprotons ( &pmacr;'s) has been measured in the range 0.18-3.56 GeV, based on 458 &pmacr;'s collected by BESS in a recent solar-minimum period. We have detected for the first time a characteristic peak at 2 GeV of &pmacr;'s originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS data with still higher statistics will allow us to study the solar modulation and the propagation in detail and to search for primary &pmacr; components.