This series of papers is concerned with the isolation and physiological properties of 3-P-glycerate phosphatase. Purification and characterization of this phosphatase was done with extracts of sugarcane leaves (31). The enzymatic hydrolysis of P-glycolate and 3-P-glycerate has many parallels. The substrates are structural analogs at each end of the glycolate pathway ( Fig. 1), but the phosphatases are distinctly different. In C3-plants' glycolate metabolism, peroxisomes, and photorespiration are active, and in these plants P-glycolate phosphatase likewise is a major enzyme and relatively more active than 3-P-glycerate phosphatase. In C4-plants the peroxisomal system is mainly restricted to the bundle sheath cells (39). where most of the P-glycolate phosphatase is located (33). In an initial survey of C,-plants more 3-P-glycerate phosphatase activity was found than P-glycolate phosphatase (30), and a major part of the 3-P-glycerate phosphatase was in the cytosol of the mesophyll cells (33), which also contain the Cg-pathway of CO. fixation (16). It is suggested that the two phosphatases regulate different metabolic routes to the same products, glycine and serine. and are involved in regulating photorespiration. That 3-P-glycerate phosphatase may be involved in a carbon shuttle system in C-plants is to be considered.MATERIALS AND METHODS Plants were grown for 3 to 6 weeks in greenhouse or field as indicated in Table I, and only mature leaves were used. Etiolated sugarcane leaves were from stem nodes kept in a dark growth chamber in vermiculite and watered with Hoagland's nutrient solution for 21 days at 23 C. Chlorella pyrenoidosa (Marburg strain) and Chlamnydomnonas reinhardtii were grown as described previously (19). Tissues were extracted immediately after harvest. The leaves were washed, blotted dry, large midribs removed, and remaining tissue diced. The leaf samples were then homogenized for 2 min at 4 C in a Waring Blendor with five volumes of a grinding medium containing 20 mm sodium cacodylate buffer at pH 6.3 and 1 mm EDTA. As indicated 2% Polyclar AT and 20 'Plants which initially fix C02 mainly by the photosynthetic carbon reduction cycle are termed C3-plants, and plants which also contain the C4-dicarboxylic acid cycle of C02 fixation in the mesophyll cells, are termed C4-plants (16). 480www.plantphysiol.org on May 9, 2018 -Published by Downloaded from
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