Isolation and characterization of chitinase isoforms from the bulbs of four species of the genus Tulipa.

Abstract

Six chitinase isoforms, designated TBC-1 to TBC-6, were purified to homogenity from the bulbs of four species (Tulipa bakeri, T. tarda, T. turkestanica, and T. praestans) of the genus Tulipa by CM-cellulose column chromatography, Butyl-Toyopearl 650M hydrophobic column chromatography, gel filtration on Sephadex G-75, and Mono-S fast protein liquid chromatography (FPLC). The chitinases had molecular weights of 30,000 and isoelectric points of 5.2 to 6.1. These chitinases were found to proteins with similar amino acid compositions and N-terminal sequences. The tulip chitinases all had two half-cystine residues, one more than gladiolus bulb class IIIb chitinase, but many fewer than chitinases of plant class I (15-17 Cys residues/mol), II (5-8 Cys residues/mol), or III (6 Cys residues/mol). The N-terminal sequences of tulip chitinases were similar to the sequence of the gladiolus chitinase, but did not resemble sequence of any class of plant chitinase. The optimal pH of these chitinases toward glycolchitin was pH 5. TBC-1 hydrolyzed (GlcNAc)6 into (GlcNAc)2, (GlcNAc)3, and (GlcNAc)4, and hydrolyzed (GlcNAc)5 into (GlcNAc)2 and (GlcNAc)3.