Endoglycosidase with broad specificity that cleaves the chitobiose core of high mannose and complex N-linked glycans. Is able to release N-glycans from diverse host glycoproteins such as human and bovine lactoferrin, immunoglobulins A and G, and ribonuclease B. Is active directly on human breast milk - a complex matrix of lipids, oligosaccharides, and proteins with disparate glycosylation types - successfully removing a significant proportion of the total amount of N-glycans. Does not recognize O-linked glycans or free human milk oligosaccharides (HMO). Endohydrolysis of the N,N'-diacetylchitobiosyl unit in high-mannose glycopeptides and glycoproteins containing the -[Man(GlcNAc)2]Asn- structure. One N-acetyl-D-glucosamine residue remains attached to the protein, the rest of the oligosaccharide is released intact. Optimum pH is 5.0. Optimum temperature is 30-45 degrees Celsius. Is heat-resistant, since the enzymatic activity is not significantly impaired by incubation at 95 degrees Celsius for 1 or 5 minutes. Constitutively expressed. Is up-regulated when cells are grown on lactose (by comparison with cells grown on glucose), or when the bacterium is incubated with human or bovine lactoferrin. EndoBI-1 might prove useful as a novel tool for diverse applications in proteomics and glycoproteomics research. Belongs to the glycosyl hydrolase 18 family.