Effect of Potassium & Other Univalent Cations on Activity of Pyruvate Kinase in Pisum sativum

Abstract

Potassium is a major component of both plant and animal organisms, yet information on the role of this element in metabolism is limited. A compilation (1) of the inorganic composition of many plant species reveals that a major portion of normal leaves contain from 1 to 4 % K+ on a dry weight basis. Potassium deficiency symptoms are noted when the K + contents of leaves range from 0.1 to 1.3 % of their dry matter. There are many general statements (3) to the effect that K+, Na+, and other ions that are present in biological materials in high concentrations function in the osmotic regulation of tissue fluids. Undoubtedly this is an important role of the so-called bulk ions, but relatively recent biochemical investigations (3) have provided convincing evidence that a series of enzyme systems require K+, NH4+ or Rb+ for activity and that the concentration of these ions needed for maximum reaction velocities is in the same range as the concentration of K+ in normal biological materials.

Pyruvate Kinase, a Possible Regulatory Enzyme in Higher Plants

“…The activation of the enzyme by mono-and divalent cations in relation to plant nutrition has been studied (14,(26)(27)(28)39), but the work to date (26,28,31) indicates that the higher plant enzyme does not show sigmoid kinetics towards PEP and is not activated by FDP. However, since neither of these properties is common to all pyruvate kinases, it was decided to re-examine the higher plant enzyme.…”

Some Properties of Partially Purified Pyruvate Kinase from Euglena gracilis Klebs var. bacillaris

“…Euglena pyruvate kinase has an absolute requirement for both Mg2" and K+, as has been found for pyruvate kinases from other sources (8,14,24). The concentration required for maximum activity was found to be 8 mM for Mg2, (as Mg SO4) and 10 mm K+ (as KCl) at pH 6.2.…”

“…Although information concerning the properties of pyruvate kinase in heterotrophic organisms is available, the situation in autotrophic organisms has not been examined extensively (8, 23,(26)(27)(28) …”

“…During the last several years the enzyme pyruvate kinase, which catalyzes this conversion, has been isolated and purified from many sources and its properties described in some detail (4-7, 12, 14. 18-20, 24).Although information concerning the properties of pyruvate kinase in heterotrophic organisms is available, the situation in autotrophic organisms has not been examined extensively (8, 23,(26)(27)(28) …”

“…Although information concerning the properties of pyruvate kinase in heterotrophic organisms is available, the situation in autotrophic organisms has not been examined extensively (8,23,(26)(27)(28) (14) have isolated pyruvate kinase from serum of latex and found that the enzyme is inhibited by citrate and Ca'+. Duggleby and Dennis (6, 7) have reported the properties of pyruvate kinase isolated from cotton seed.…”