Enzymatic properties of endo- β- N-acetylglucosaminidases from developing tomato fruits and soybean seeds: substrate specificity of plant origin endoglycosidase

Abstract

Substrate specificity and some other enzymatic properties of partial purified endo- β- N-acetylglucosaminidases (endo- β-GlcNAc-ase) from developing soybean seeds ( Glycine max, Endo-GM) and developing tomato fruits ( Lycopersicum esculentum, Endo-LE) were studied. The substrate specificity of these two endoglycosidases was explored and compared with regard to various pyridylaminated N-glycans derived from some naturally occurring glycoproteins. For Endo-GM and Endo-LE, several high mannose-type sugar chains bearing α1–2 mannosyl residue(s), Man 9-6GlcNAc 2–PA (PA is pyridylamino) (80–100% relative hydrolysis), were most favored substrates followed by Man 5GlcNAc 2–PA (32% for Endo-LE, 43% for Endo-GM), a typical hybrid-type structure (GlcNAc 1Man 5GlcNAc 2–PA; 34% for Endo-LE, 37% for Endo-GM), and then the common core pentasaccharide of N-glycan (Man 3GlcNAc 2–PA; 9% for Endo-GM and 16% for Endo-LE). On the contrary, both Endo-GM and Endo-LE could barely hydrolyze the xylose-containing N-glycans (Man 3Xyl 1GlcNAc 2–PA, Man 3Fuc 1Xyl 1GlcNAc 2–PA) found ubiquitously in plant cells. The molecular mass of these two endoglycosidases was approximately 62 kDa by gel filtration and both Endo-GM and Endo-LE showed maximal activities for Man 6GlcNAc 2–PA in a weak acidic region (pH 6.0–6.5).