This study characterized chitinase activities from the fungus Mucor mucedo, identifying two distinct forms: a soluble supernatant chitinase and a membrane-bound microsomal chitinase. Both enzymes showed similar basic properties, including pH optima around 5.5-5.65 and comparable substrate affinity. However, the microsomal form exhibited zymogenic (inactive precursor) behavior, becoming activated during storage or when treated with proteases like trypsin, while the supernatant form remained stable. The microsomal chitinase required phospholipids for activity, as demonstrated by inactivation following phospholipase treatment. The authors proposed that the membrane-bound chitinase acts as a morphogenetic autolysin involved in fungal hyphal growth, potentially working in concert with chitin synthase to regulate cell wall remodeling. The presence of multiple endogenous protease activities in microsomes suggests these enzymes may physiologically activate the chitinase zymogen during normal growth processes.

Key findings

• Mucor mucedo produces two chitinase forms: a soluble supernatant form and a membrane-bound microsomal form with similar kinetic properties but different stability profiles
• The microsomal chitinase is a zymogen that can be activated by proteolytic treatment and undergoes endogenous activation during incubation, while the supernatant form is constitutively active
• Microsomal chitinase activity requires intact phospholipids, as demonstrated by complete loss of activity following phospholipase A treatment in a calcium-dependent manner
• Serine protease activity is involved in zymogenic activation, based on inhibition by PMSF (phenylmethanesulphonyl fluoride)
• The membrane-bound chitinase is proposed to function as a morphogenetic autolysin regulating chitin deposition during hyphal growth and branching