Molecular properties of acetylcholinesterase purified from Lygus hesperus Knight (Hemiptera:Miridae)

Molecular properties of acetylcholinesterase (AChE, EC 3.1.1.7) purified from Lygus hesperus Knight were characterized by sucrose gradient centrifugation, non-denaturing, denaturing, and two-dimensional polyacrylamide gel electrophoresis, isoelectric focusing, and inhibition by paraoxon. AChE was found to be a globular enzyme with three distinct molecular forms. The major form, accounting for about 89% of total AChE activity, was a hydrophilic form (b) with a sedimentation coefficient of 7.3 S. Two other minor forms, which were recovered in either non-denaturing or denaturing gel electrophoresis but not in the centrifugation, were hydrophilic (a) and amphiphilic (c) forms, accounting for about 4 and 7% of total AChE activity, respectively. The molecular weights for the native and reduced protein were 199,000 and 94,000 for the hydrophilic a form, 150,000 and 79,000 for the hydrophilic b form, and 82,000 and 86,000 for the amphiphilic form, indicating that the molecular forms a and b were dimers while c was a monomer. All three molecular forms appeared to have very similar isoelectric points (7.4), and responded similarly to inhibition by paraoxon. These similarities may indicate structural similarity among these molecular forms of AChE.