Analysis of highly clustered O-glycosylated sites can be challenging due to the diverse site occupancy (macroheterogeneity) and close proximity of O-glycosylation sites in glycoproteins. Parallel analysis of a native and denatured glycoprotein digested with O-Glycoprotease (IMPa) can help to obtain more complete information. Longer incubation times (18 hours) and more enzyme may be necessary in some cases. In addition, O-Glycoprotease (IMPa) does not cleave between two adjacent O-glycosylated amino acids.