Alkaline inorganic pyrophosphatase from orchid leaves

An alkaline inorganic pyrophosphatase (IP) from leaves of an orchid, Aranda Christine 130 (Arachnis hookerana var. luteola × Vanda Hilo Blue) was purified by acetone precipitation and chromatography on Sephadex G-75 and DEAE-cellulose. The IP gave a single band on non-denaturing gel electrophoresis at pH 8.3 and its M, determined by gel filtration, was 28 000. The pH optimum was 9 and the IP required Mg²⁺ for its activity and stability. The IP exhibited high specificity for PPi and attained a maximum activity at a Mg²⁺: PPi ratio of 10:1. Other cations tested could not replace Mg²⁺ and they were also found to be inhibitory. The IP was also inhibited by EDTA and F^? but not by iodoacetamide.