Some properties of pea cholinesterase and its activity in plant parts at different growth stages

Cholinesterase activity was studied in 2 to 10-week-old pea plants cultivated under artificial illumination. Free and membrane-bound forms of the enzyme were separated by extracting the enzyme from pea shoots with buffers differing in ionic strength. The ratio of the free cholinesterase to the membrane-bound one fluctuated between 1 : 1 and 1 : 2.5. The free cholinesterase was inhibited by neostigmine (0.1mmoll-1) by 50%, the membrane-bound enzyme by 90%. The pH optimum of cholinesterase activity was 8.5, the temperature optimum 37 °C. The enzyme activity was increased by some cations in this order: Mg2+ < < K+. The Km value for the substrate S-acetylthiocholine iodide was 250 μmoll-1, the enzyme activity being inhibited by concentrations higher than 3 mmoll-1 of this substrate.