Cloning and Expression of a Fungal l-Arabinitol 4-Dehydrogenase Gene

l-Arabinitol 4-dehydrogenase (EC 1.1.1.12) was purified from the filamentous fungusTrichoderma reesei (Hypocrea jecorina). It is an enzyme in the l-arabinose catabolic pathway of fungi catalyzing the reaction from l-arabinitol tol-xylulose. The amino acid sequence of peptide fragments was determined and used to identify the corresponding gene. We named the gene lad1. It is not constitutively expressed. In a Northern analysis we found it only after growth onl-arabinose. The gene was cloned and overexpressed inSaccharomyces cerevisiae, and the enzyme activity was confirmed in a cell extract. The enzyme consists of 377 amino acids and has a calculated molecular mass of 39,822 Da. It belongs to the family of zinc-binding dehydrogenases and has some amino acid sequence similarity to sorbitol dehydrogenases. It shows activity towardl-arabinitol, adonitol (ribitol), and xylitol withKm values of about 40 mm towardl-arabinitol and adonitol and about 180 mmtoward xylitol. No activity was observed with d-sorbitol,d-arabinitol, and d-mannitol. NAD is the required cofactor with a Km of 180 µm. No activity was observed with NADP.