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Effect of phospholipids on thyroid 5'-nucleotidase
1Department of Physical Chemistry, Medical Academy, Bialystok, Poland.
Acta Biochimica Et Biophysica Hungarica
|January 1, 1990
Summary
Thyroid plasma membranes contain 5'-nucleotidase, an enzyme whose activity is influenced by membrane fluidity, not phospholipids. This enzyme remains active even after lipid removal, indicating phospholipids are not essential cofactors.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Thyroid plasma membranes contain 5'-nucleotidase, an enzyme involved in nucleotide metabolism.
- The role of membrane lipids, specifically phospholipids, in regulating 5'-nucleotidase activity is not fully understood.
Purpose of the Study:
- To investigate the relationship between phospholipids and 5'-nucleotidase activity in thyroid plasma membranes.
- To determine if phospholipids are essential cofactors for 5'-nucleotidase function.
- To examine the influence of membrane physical state on enzyme activity.
Main Methods:
- Separation of phospholipids from 5'-nucleotidase using Sephadex G-200 gel filtration.
- Assay of 5'-nucleotidase activity after lipid removal and reassociation.
- Analysis of enzyme activity using Arrhenius plots to determine thermal transitions.
Main Results:
- 5'-nucleotidase retained activity after phospholipid removal.
- Reassociation with phospholipids had a minimal effect on enzyme activity.
- Arrhenius plots revealed a phase transition at 28°C, indicating temperature-dependent changes in membrane fluidity affecting enzyme activity.
- Phospholipids were not found to be obligatory cofactors for 5'-nucleotidase.
Conclusions:
- Phospholipids are not essential cofactors for thyroid 5'-nucleotidase activity.
- The enzyme's activity is modulated by the physical state of the membrane bilayer, as evidenced by the biphasic Arrhenius plot.
- These findings contribute to understanding the regulation of membrane-bound enzymes in thyroid cells.