Amino sugar metabolism in erythrocytes

• Published in: Biochimica et biophysica acta Vol. 170; no. 1; pp. 77 - 87
• Main Authors: Kornfeld, Rosalind, Noll, Carolyn
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 12.11.1968
• Subjects: Alanine Transaminase; Animals; Bone Marrow - enzymology; Bone Marrow Cells; Carbon Isotopes; Erythrocytes - enzymology; Erythrocytes - metabolism; Fru-6- P; Fructose - metabolism; fructose 6-phosphate; GlcN-6- P; GlcNAc; Glucosamine - biosynthesis; glucosamine 6-phosphate; N-acetylglucosamine; N-acetylneuraminic acid; NANA; Rabbits; Reticulocytes - enzymology; Reticulocytes - metabolism; Fru-6- P; NANA; GlcNAc; GlcN-6- P
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/0304-4165(68)90162-1

The ability of rabbit erythrocytes to synthesize glucosamine and convert it to UDP- N-acetylglucosamine (UDP-GlcNAc) has been measured in mature erythrocytes, in reticulocytes, and in the immature bone marrow erythroid cells. The cells were incubated with either [ 14C]fructose which can be converted via fructose 6-phosphate (Fru-6- P) to glucosamine 6-phosphate (GlcN-6- P) by the enzyme l-glutamine- d-fructose-6-phosphate amidotransferase (EC 2.6.1.16) and then to UDP-GlcNAc, or with [ 14C]glucosamine which enters the pathway as GlcN-6- P, thus bypassing the first enzymatic reaction, which in other tissues is the rate-limiting step in UDP-GlcNAc biosynthesis. Mature erythrocytes were unable to incorporate label from either precursor into UDP-GlcNAc and the [ 14C]glucosamine accumulated as GlcN-6- P, indicating that at least the first two steps in the pathway were inoperative. Reticulocytes incorporated label from both precursors into UDP-GlcNAc, but more efficiently from [ 14C]fructose. Marrow erythroid cells incorporated label into UDP-GlcNAc from [ 14C]glucosamine two-fold better than reticulocytes on a per cell basis (4.2. as against 1.9 mμmoles/2 h per 2.2·10 8 cells) and from [ 14C]fructose about twenty-fold better (0.21 as against 0.01 mμmole/2 h per 2.2·10 8 cells). These results indicate that l-glutamate- d-fructose-6-phosphate amidotransferase, the initial and rate-limiting enzymes of the amino sugar biosynthetic pathway, is active in marrow erythroid cells but declines in activity by about twenty-fold at the reticulocyte stage and is absent from mature erythrocytes. The activity of the second enzyme of the pathway declines at a later stage.