Estimation of monoamine oxidase concentrations in soluble and membrane-bound preparations by inhibitor binding.

A modification of the [3H]-pargyline labelling technique is presented for determining the active-site concentration of monoamine oxidase in soluble preparations. Kinetic considerations show that the rate of reaction of MAO-A with low concentrations of free pargyline will be very much slower than that of MAO-B. Failure to use adequate reaction times for the concentration of pargyline added can lead to gross underestimation of the quantity of MAO-A present.