Corn phosphoglycolate phosphatase: purification and properties

✍ Scribed by P. Hardy; P. Baldy

• Publisher: Springer-Verlag
• Year: 1986
• Tongue: English
• Weight: 844 KB
• Volume: 168
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00402970

✦ Synopsis

Phosphoglycolate phosphatase (EC 3.1.3.18), isolated from maize leaf bundle sheath, was purified 200-fold to a specific activity of about 99 gmol mg-1 protein, rain -a. The purification procedure included Sephadex G-75 filtration, and diethylaminoethyl-cellulose and Phospho-Ultrogel A6R chromatography. This partially purified enzyme exhibited optimum activity over a broad pH range, from pH 6.3 to pH 8.0. It displayed a very high degree of specificity for phosphoglycolate and required a divalent cation to be active; Mg z+ was the most effective activator. Saturation curves of the Michaelis-Menten type were observed both with phosphoglycolate (Km=0.57 retool.1 -a) and with Mg 2+ (Km= 0.015 retool-l-a). The activation constant for Mg 2+ was unchanged when the pH was raised from 7.0 to 8.0. These results indicate that variations of stromal pH and Mg 2+ during the darklight transition could not directly modifiy the activity of the phosphoglycolate phosphatase in maize bundle-sheath chloroplasts. The undissociated protein showed a pI of 4.95, as determined by isoelectric focusing. For the native phosphatase a molecular mass of about 61 500 Da was estimated by polyacrylamide gradient gel electrophoresis. The subunit was found to have a relative molecular mass of 3t 500 Da by sodium dodecyt sulfate-polyacrylamide gel electrophoresis. It is concluded that maize phosphoglycolate phosphatase is a dimer. Key words" Phosphoglycolate phosphatase -Photorespiration -Photosynthesis (C4) -Zea (phosphoglycolate phosphatase).