Occurrence of Nicotinamide Adenine Dinucleotide Phosphatelinked Glyoxylate Reductase in Nonphotosynthetic Xylem Tissue of Perennials

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Abstract
Xylem extracts of poplar tree contained glyoxylate reductase specific for NADPH. By isoelectric focusing in the pH ranges 3.5 to 10 or 4 to 6, the enzyme exhibited a single peak of activity at pH 5.4. The enzyme showed essentially no activity toward hydroxypyruvate, pyruvate, or NADH. The reaction was optimal at pH 6.0 in phosphate buffer and the activity profile exhibited a sharp and narrow pH profile with half-maximal velocities at about pH 7.0. The Km of the enzyme for glyoxylate was 0.11 millimolar. The xylem tissue of poplar tree exhibited high levels of enzyme activity (30 micromoles per gram dry weight per hour) even in the wintering stage and a slight change in activity occurred in spring and fall at the time when metabolism transition occurs.