37] 4-Hydroxybenzoate polyprenyltransferase from rat liver

Abstract

This chapter focuses on 4-hydroxybenzoate polyprenyltransferase from rat liver. 4-Hydroxybenzoate polyprenyltransferase is a key enzyme in ubiquinone synthesis because it catalyzes the step that brings together the precursor of the benzoquinone ring and the polyisoprenoid side chain. The substrates are 4-hydroxybenzoate derived from tyrosine metabolism, and polyprenyl pyrophosphates derived from mevalonic acid and the product is 3-polyprenyl-4-hydroxybenzoate (PPHB) and pyrophosphate. The 3-polyprenyl-4-hydroxybenzoate, after hydroxylation, decarboxylation, and methylation, gives rise to ubiquinone. When nonaprenyl pyrophosphate (NPP) was used as a source of polyprenyl side chain in rat liver, 3-nonaprenyl-4-hydroxybenzoate was the major product but there was also minor incorporation into 3-octaprenyl-4 hydroxybenzoate. The formation of octaprenyl derivative might be due to observed contamination of solanesol, which was used for the preparation of nonaprenyl pyrophosphate. In rat liver, the addition of IPP along with NPP resulted in formation of a minor amount of decaprenyl derivative but still nonaprenyl derivative was the major component of the products formed. Whereas in guinea pig liver, the addition of IPP along with NPP resulted in formation of octa, nona, and decaprenyl derivatives all in significant quantities.