Phytases catalyse the hydrolysis of phytate (myo-inositol hexakisphosphate) to myo-inositol and inorganic phosphate. In this study genes encoding novel phytases from two different filamentous fungi, Aspergillus terreus strain 9A-1 and Myceliophthora thermophila were isolated. The encoded PhyA phytase proteins show 60% (A. terreus) and 489'0 (M. thermophila) identity, respectively, to the PhyA of Aspergillus niger and have 21-29% identity compared to other histidine acid phosphatases. All three PhyA proteins, in contrast to the A. niger pH 25-optimum acid phosphatase, prefer phytic acid as substrate and show enzyme activity at a broad range of acidic pH values. Based on their enzyme characteristics and protein sequence homology, the phytases form a novel subclass of the histidine acid phosphatase family.
Phytase is a high molecular weight acid phosphatase. The structure has an alpha/beta-domain similar to that of rat acid phosphatase and an alpha-domain with a new fold.
When Kosslyn, Ball, and Reiser asked subjects to scan a memorized picture, they found a strong positive linear relationship between distance scanned and reaction time. However, more recent research has suggested that this result may be as much a function of the demand characteristics of the experiment as a reflection of any structural properties of the image. To further test this possibility with complex stimuli, college subjects were either presented with Kosslyn's pictorial stimuli or verbal descriptions of same in a "nonexperiment" and were asked to predict their scanning times. The subjects were able to produce high linear correlations between scanning distance and predicted scanning time. This result is consistent with a demand characteristics explanation of the correlation between distance and reaction time that is obtained in actual image-scanning studies.
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