Abstract
ABSTRACTA suitable method for extraction of floridoside phosphate synthase (FPS, UDP‐galactose: sn‐3‐glycerol phosphate: 1→2′α‐D‐galactosyl transferase)from Porphyra perforata J. Ag. was developed. Two assay methods for enzyme activity were utilized, one measuring the amount of floridoside formed by using gas‐liquid chromatography, the other measuring the sn‐3‐glycerol phosphate‐dependent formation of UDP; both assays gave similar results. FPS is a soluble protein, and FPS activity in the extract as determined by the amount of product formed in vitro compared well with the in vivo rate of floridoside synthesis (4–7 μMmol product formed·h−1·g−1 fresh wt). The rate of product formation in vitro was linear up to 45 min and proportional to protein concentration in the assay mixture. The temperature optimum was 30–35° C. FPS was active over a range of pH values from 7.0–8.5. It was stable in concentrated solutions in the presence of 0.3 M ammonium sulfate, but activity was lost in diluted solution (protein concentration below 0.2 mg·mL−1) or below 0.2 M ion strength. The data suggest that FPS may be an oligomeric protein which occurs free in the cytoplasm or loosely bound to a membrane. It may also be a regulatory protein controlling the overall rate of synthesis of floridoside in vivo.
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