For instance, all seminal plasma PCI lacked an NH2-terminally cleaved peptide, although this peptide was ten residues instead of six. This ten-residue NH2-terminal peptide is highly positively charged and thus likely affects the functional properties of PCI. The N-glycans of seminal plasma PCI consist mainly of corefucosylated, biantennary lewisX and/or lewisY-capped structures. They are completely devoid of 1173097-76-1 sialic acids, and therefore differ markedly in sequence from those previously identified in blood PCI. Our previous study showed that the N-glycans from blood PCI consist of bi-, tri, and tetra-antennary structures of which the most abundant structure is a non-fucosylated biantennary glycan with both antennae capped with sialic acid. A small fraction of the blood PCI N-glycans carried sialyl-LewisX epitopes. The N-glycans linked to urinary PCI consist of mainly core fucosylated, biantennary structures that are to a great extent sialylated at the end of the antennae. Additionally, a portion of the urinary PCI glycans have antennae composed of lacdiNAc, a rarer sequence that has been observed in neither blood nor seminal plasma PCI N-glycans. The 146368-13-0 source of urinary PCI has not been completely identified so far. However, Radtke et al. have shown that PCI is synthesized in tubular cells of the kidney, suggesting that the kidney is a source for urinary PCI. The differences observed in N-glycan structures of PCI in seminal plasma, urine and blood supports this conclusion and demonstrates that the N-glycosylation of PCI displays a highly tissue-specific expression. A recent study revealed the overall seminal plasma N-glycome, which consists of bi-, tri- and tetraantennary sequences, of which several contain lewisX and/or lewisY-capped structures. In contrast to the N-glycans of seminal plasma PCI, the seminal plasma N-glycome also contains a substantial portion of highmannose as well as sialylated structures. Moreover, sialylated glycans are abundant in seminal plasma from some individuals and minor in others according to this glycomics analysis, while they appear to be totally absent in PCI. Our results thus demonstrate that PCI neither contributes to the individual differences in sialylated N-glycans nor to the high-mannose structures observed in the seminal plasma glycome. Similar observations have been reported previously and are presumably due to the high concentration of PSA in semen. Moreover, N-glycans alone did not significantly contribute to the k2 for PCI inhibition of PSA. However, the combined loss of Nglycans and the D6-NH2-terminus significantly enhanced the reaction, indicating that these structures together contribute to the slow PSA-PCI reaction velocity. These results may be explained by the possibility th
