UDP-N-acetylhexosamine pyrophosphorylase (antigen X, AGX, sperm-associated antigen 2, [Includes: UDP-N-acetylgalactosamine pyrophosphorylase (AGX-1); UDP-N-acetylglucosamine pyrophosphorylase (AGX-2)], UAP1 SPAG2)

Function

• UDP-GlcNAc biosynthesis from Fru-6-P, 4th (last) step
• converts UDP & GlcNAc-1-P into UDP-GlcNAc, & UDP & GalNAc-1-P into UDP-GalNAc
• isoform AGX1 has 2-3X higher activity towards GalNAc-1-P
• isoform AGX2 has 8X more activity towards GlcNAc-1-P

UTP + N-acetyl-alpha-D-glucosamine 1-phosphate
              <-->  diphosphate + UDP-N-acetyl-D-glucosamine

Structure

• monomer & homodimer
  • isoform AGX1 is a homodimer
  • isoform AGX2 is a monomer

Compartment

• cytoplasm
• in spermatozoa, localized to the principal piece of the tail, the neck region of the head & to a lesser extent, the midpiece of the tail

Alternative splicing

named isoforms=3

Expression

• widely expressed
• isoform AGX1 is more abundant in testis than isoform AGX2
• isoform AGX2 is more abundant than isoform AGX1 in somatic tissue
• expressed at low level in placenta, muscle & liver

Pathology

• antigen implicated in antibody-mediated male infertility

More general terms

• enzyme

Database

• OMIM: https://mirror.omim.org/entry/602862
• UniProt: http://www.uniprot.org/uniprot/Q16222.html