Fructose metabolism in plants. Isolation and properties of pea seed frucktokinase.

Fructokinase from pea (Pisum sativum L.) seed has purified 100-fold. The enzyme required reduced sulfhydryl groups for activity. It also exhibits an absolute requirement for potassium ions (Km = 3 mM) and is unstable when not stored with a high concentration of potassium ions. The isoelectric point of the enzyme is 4.7 and it has a molecular weight of 44 000 +/- 700 daltons as determined by molecular sieve chromatography and sedimentation velocity techniques. A Hill plot of the potassium ion data suggests that two potassium sites are present on the enzyme. The MgATP saturation curve was non-Michaelis-Menten with a slight positive cooperativity. Pea seed fructokinase is highly specific for fructose and ATP. A comparison of pea seed fructokinase properties and those of liver and bacterial origin is presented.