The reactor calorimetric technique was employed to study a homogeneous, liquid-phase
ketonization reaction used in fine chemical syntheses, where an unsaturated alcohol and
unsaturated ether condense to form an unsaturated ketone with higher molecular weight. The
experiments were carried out in a calorimetric reactor (RC-1) and the data obtained allowed
the determination of reaction heat flow versus time, overall reaction enthalpy, and reaction
course for experiments at different temperatures. Using the latter data, the conversion versus
time behavior was determined. These data were modeled assuming a pseudo-first-order kinetics
and an Arrhenius-type temperature dependence of the specific reaction rate. Comparison between
these results and the usual concentration versus time experimental data obtained with a different
technique was satisfactory.
Aspergillus fumigatus phytase has previously been identified as a phytase with a series of favourable properties that may be relevant in animal and human nutrition, both for maximising phytic acid degradation and for increasing mineral and amino acid availability. To study the natural variability in amino acid sequence and its impact on the catalytic properties of the enzyme, we cloned and overexpressed the phytase genes and proteins from six new purported A. fumigatus isolates. Five of these phytases displayed < or= 2 amino acid substitutions and had virtually identical stability and catalytic properties when compared with the previously described A. fumigatus ATCC 13073 phytase. In contrast, the phytase from isolate ATCC 32239 ( Sartorya fumigata, the anamorph of which was identified as A. fumigatus) was more divergent (only 86% amino acid sequence identity), had a higher specific activity with phytic acid, and displayed distinct differences in substrate specificity and pH-activity profile. Finally, comparative experiments confirmed the favourable stability and catalytic properties of A. fumigatus phytase.
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