Abstract
An alkaline, Mg 2+-dependent inorganic pyrophosphatase has been isolated from previously isolated spinach chloroplast. The activity of the enzyme was increased 100-fold, with a 42% yield, upon purification from the total soluble chloroplast enzymes. The pH optimum for the enzyme shifts from 9.0 at 5 mM Mg 2+ to 7.0 at 40 mM Mg 2+. The substrate for the reaction appears to be magnesium pyrophosphate, and anionic pyrophosphate is an effective inhibitor. There seems to be also an activating effect of Mg 2+ on the enzyme at pH 7. No other cation substitutes for Mg 2+ in activating the hydrolysis of pyrophosphate. Among anions tested, only F − caused severe inhibition. The enzyme is inactive towards fructose 1,6-diphosphate, thiamine pyrophosphate, ATP, and ADP. The possibility that this enzyme is subject to metabolic regulation is discussed in relation to an indicated role of pyrophosphate in the regulation of photosynthetic carbon reduction.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Bioenergetics
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