PAEP Full-Length MS Protein Standard (NP_002562), Labeled with [U- 13C6, 15N4]-L-Arginine and [U- 13C6, 15N2]-L-Lysine, was produced in human 293 cells (HEK293) with fully chemically defined cell culture medium to obtain incorporation efficiency at Creative-Proteomics. This gene is a member of the kernel lipocalin superfamily whose members share relatively low sequence similarity but have highly conserved exon/intron structure and three-dimensional protein folding. Most lipocalins are clustered on the long arm of chromosome 9. The encoded glycoprotein has been previously referred to as pregnancy-associated endometrial alpha-2-globulin, placental protein 14, and glycodelin, but has been officially named progestagen-associated endometrial protein. Three distinct forms, with identical protein backbones but different glycosylation profiles, are found in amniotic fluid, follicular fluid and seminal plasma of the reproductive system. These glycoproteins have distinct and essential roles in regulating a uterine environment suitable for pregnancy and in the timing and occurrence of the appropriate sequence of events in the fertilization process. A number of alternatively spliced transcript variants have been observed at this locus, but the full-length nature of only two, each encoding the same protein, has been determined.