Glucosaminephosphate synthase of human liver

Area of Science:

• Biochemistry
• Enzymology
• Human Physiology

Background:

• Human liver possesses glucosaminephosphate synthase (EC 5.3.1.19), an enzyme involved in nucleotide sugar biosynthesis.
• Enzyme activity is typically lost during extraction procedures, hindering biochemical analysis.
• Previous studies indicated similar enzyme activity in rat liver, but human liver data was limited.

Purpose of the Study:

• To characterize the activity and properties of glucosaminephosphate synthase in human liver extracts.
• To investigate methods for stabilizing the enzyme during extraction and purification.
• To determine the role of human liver glucosaminephosphate synthase in UDP-N-acetylglucosamine synthesis.

Main Methods:

• Extraction of human liver tissue in the presence of 1% isopropanol to stabilize enzyme activity.
• Ammonium sulfate precipitation to isolate glucosaminephosphate synthase.
• Enzyme inhibition assays using UDP-N-acetylglucosamine.
• Enzyme characterization including resistance to trypsin and glucose 6-phosphate incubation.

Main Results:

• Isopropanol (1%) effectively prevented the rapid loss of glucosaminephosphate synthase activity in human liver extracts.
• Stabilized human liver enzyme activity was comparable to that reported for rat liver.
• The enzyme was inhibited by UDP-N-acetylglucosamine (half-maximal inhibition at 6 μM), suggesting its role in synthesis.
• Unlike the rat enzyme, the human enzyme was resistant to trypsin and did not undergo conversion with glucose 6-phosphate.

Conclusions:

• Glucosaminephosphate synthase is present and active in human liver, playing a significant role in UDP-N-acetylglucosamine synthesis.
• Isopropanol stabilization is a critical method for studying this enzyme in human liver.
• Human liver glucosaminephosphate synthase exhibits distinct properties compared to its rat counterpart, particularly regarding stability and substrate interaction.