Rat striatal synaptosomes as a model system for studying the inhibition of dihydropteridine reductase activity

The distribution of dihydropteridine reductase between soluble and particulate fractions in synaptosomes parallels that of lactate dehydrogenase, but not monoamine oxidase. Ki and I50 values for inhibitors obtained with the enzyme-rich P2 fraction and its twice-washed fraction (P2W2) were essentially the same, and were similar to those obtained with highly purified human liver enzyme. Dihydropteridine reductase inhibitory potency of multi-ring compounds containing a catechol-moiety was greater than that of single ring catecholic compounds, which in turn was greater than that of p-hydroxy-phenolic compounds. The P2 fraction of rat striatal synaptosomal preparations may serve as a convenient source of dihydropteridine reductase for studying the inhibition of this enzyme.