Isolation, purification, and characterization of two thermostable endo-1,4-ß-D-glucanase forms from Opuntia vulgaris.

Four endoglucanase temperature isoforms (T (30), T (50), T (70), and T (90)) were identified and purified from the cladodes of the xerophytic plant Opuntia vulgaris. These isoforms exhibited optimum catalytic activity at 30 °C, 50 °C, 70 °C, and 90 °C and yielded an apparent molecular mass of 150, 20, 74, and 45 kDa, respectively, on gel filtration chromatography. These isoforms were purified 24-, 25-, 29-, and 27-fold with a yield of 15%, 12%, 17%, and 19% and having a specific activity of 120, 125, 144, and 136 U/mg, respectively. The thermostable T (70) and T (90) isoforms exhibited optimum activity at pH 4.5 and 7 and also yielded a molecular weight of 66 and 36 kDa, respectively, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The T (70) had a K (m) of 43 mM and a V (max) of 12.5 µmol min(-1) µg(-1) of protein, and the T (90) isoform had a K (m) of 40 mM, with an apparent V (max) of 10 µmol min(-1) µg(-1) of protein. Western blot, immunodiffusion, and in vitro inhibition assays established the reactivity of the T (90) isoform with polyclonal anti-T (90) antibody raised in rabbit. Cross-reactivity of this antibody with the T (70) endoglucanase isoform was also noted.

Isolation, purification, and characterization of thermophilic T80 isoenzyme of xylose isomerase from the xerophyte Cereus pterogonus.

A thermostable isoenzyme (T(80)) of xylose isomerase from the eukaryote xerophyte Cereus pterogonus was purified to homogeneity by precipitation with ammonium sulfate and column chromatography on Dowex-1 ion exchange, with Sephadex G-100 gel filtration, resulting in an approximately 25.55-fold increase in specific activity and a final yield of approximately 17.9%. Certain physiochemical and kinetic properties (K(m) and V(max)) of the T(80) xylose isomerase isoenzyme were investigated. The molecular mass of the purified T(80) isoenzyme was 68 kD determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Polyclonal antibodies against the purified T(80) isoenzyme recognized a single polypeptide band on Western blots. The activation energy required for the thermal denaturation of the isoenzyme was determined to be 61.84 KJ mol(-1). The use of differential scanning calorimetry established the melting temperature of the CPXI isoenzyme to be 80°C, but when studied with added metal ions, melting temperature increases to more than the normal. Fluorescence spectroscopy of T(80) isoenzymes yielded an emission peak with λ(em) at 320 nm and 340 nm, respectively, confirming the presence of Trp residue in these proteins. Electron paramagnetic resonance (EPR) analysis at liquid nitrogen temperature established the presence of Mn(2+) and Co(2+) associated with each isoenzyme. These enzyme species exhibited different thermal and pH stabilities compared to their mesophilic counterparts and offered greater efficiency in functioning as a potential alternate catalytic converter of glucose in the production of high-fructose corn syrup (HFCS) for the sweetener industry and for ethanol production.