Spectroscopic characterization of human liver pterin 4a-carbinolamine dehydratase.

Abstract

The hepatic hydroxylation of phenylalanine catalyzed by phenylalanine hydroxylase (PAH), is dependent on tetrahydrobiopterin (BH4) and two additional enzymes, pterin 4a-carbinolamine dehydratase (PCD) and dihydropterin reductase (1). PCD, previously named “phenylalanine hydroxylase stimulating protein”, catalyzed the conversion of 4a-OH BH4, an intermediate product in hydroxylation reaction, to quinonoid dihydrobiopterin and water (3). It was proposed that PCD play a key role in preventing the formation of 7-pterins which are characteristic for primapterinuria, a new variant form of hyperphenylalaniemia (4,5). The PCD was purified from rat and human liver and partially characterized (2,6). The primary structure of purified enzyme was determined and it was been found that PCD is identical to a homeodomein-containing protein involved in regulation of transcription (7). These facts suggest on a double role of the dehydratase in the cell. In present work we undertook the further characterization of PCD by means of fluorescence spectroscopy.