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Plant and Cell Physiology, 1990, Vol. 31, No. 2 261-266
© 1990

Article

Proton Pumping Pyrophosphatase in a High Density Fraction of Radish Microsomes

Francesco Macrì and Angelo Vianello

Institute of Plant Protection, Section of Plant Physiology and Biochemistry, University of Udine via Cotonificio 108, I-33100 Udine, Italy

Radish (Raphanus sativus L.) microsomal vesicles show a vanadate- ánd nitrate-insensitive, and imidodiphosphate-sensitive electrogenic transport of protons dependent upon addition of inorganic pyrophosphate (PP) or ADP. The activity is detectable in preparations from 24 h-old seedlings and increases about 3 fold in vesicles from 72 h-old seedlings. The ADP-dependent proton uptake, being prevented by inorganic pyrophosphatase, used as a PP scavenging system, can be ascribed to enzymes utilizing ADP and producing PP which appears the only substrate for the proton pumping PPase. The H+-PPase has a Km of ca. 10 µM for the translocating function and 20 µM for the hydrolytic activity. It has a pH optimum near to 7.0 and is stimulated by certain monovalent cations (K+, Rb+ and Cs+). The majority of this activity is associated with a high density (35–45% sucrose interface) fraction which is enriched for vanadate-sensitive, nitrate-insensitive ATPase activity.

(Received September 11, 1989; Accepted December 22, 1989)
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