Intra- and extracellular isoforms of PR-3 class chitinase in virus-infected cucumber plants.

Cucumber (Cucumis sativus L. cv. Laura) contains three different isoforms of chitinase (EC 3.2.1.14), thought to be involved in the defense against a pathogen. Using a highly specific rabbit antiserum raised against a predominant, extracellularly localized, virus-inducible acidic chitinase (p28), two additional enzyme isoforms with differential mode of compartmentalization were identified. Immunoblot analysis of the fractionated plant extracts separated by denaturing and native (anodic and cathodic) polyacrylamide gel electrophoresis (PAGE) revealed that the chitinase p25 (M(r) 25.5 K), is a basic, extracellular isoform and the chitinase p24 (M(r) 24.6 K) is an acidic, probably intracellular isoform of the enzyme.