Description:
<jats:title>Abstract</jats:title><jats:p>Four enzymes with phospholipase A<jats:sub>1</jats:sub> (PLA<jats:sub>1</jats:sub>) activity were purified from the fruiting bodies of the basidiomycete <jats:italic>Armillaria ostoyae</jats:italic>. The enzymes (PLA<jats:sub>1</jats:sub>‐1, ‐2, ‐3 and ‐4) showed similar isoelectric points (4.3, 3.9, 4.0 and 4.0) and apparent molecular masses in the range of 35–47 kDa. Mass spectrometric analyses of proteolytic fragments revealed sequences homologous to α/β‐hydrolase fold enzymes. The enzymes share one conserved region with fungal phospholipases B and the active site sequence with bacterial esterases and PLA<jats:sub>1</jats:sub>s. PLA<jats:sub>1</jats:sub>‐1 cleaves phospholipids and lysophospholipids with an optimum activity at pH 5.3. In contrast, PLA<jats:sub>1</jats:sub>‐2, ‐3 and ‐4 are characterized by broad pH optima in the slightly acidic to neutral range and are additionally capable of hydrolyzing mono‐ and diglycerides as well as fatty acid methyl esters. All enzymes favor glycerol‐based lipids with a single medium‐sized fatty acid moiety in the <jats:italic>sn</jats:italic>‐1 position but show reduced activity towards the corresponding 1,2‐diacyl derivatives with bulky long‐chain or inflexible saturated fatty acid moieties in the <jats:italic>sn</jats:italic>‐2 position. The enzymes prefer zwitterionic phospholipid substrates and are unable to hydrolyze triglycerides. From the selectivity of these broad‐spectrum α/β‐hydrolase fold enzymes towards the different classes of their substrates a regiospecific steric hindrance and a head group recognition are concluded.</jats:p>