The invention relates to the field of glycoprotein processing in transgenic plants used as cost efficient and contamination safe factories for the production of recombinant biopharmaceutical proteins or pharmaceutical compositions comprising these. The invention provides plants and plant cells comprising of functional mammalian enzyme providing N-glycan biosynthesis that is normally not present in plants, for example mammalian β 1,4-galactosyltransferase, said plants or plant cells additionally comprising at least a second mammalian protein or functional fragment thereof, for example a mammalian antibody, that is normally not present in plants.