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Reduced membrane protein methylation in red cells of the McLeod blood group phenotype
E Wainfan1, M Kilkenny, C Johnson
1Lindsley F. Kimball Research Institute, New York Blood Center, New York.
Abstract:
Red cells (RBCs) contain an abundance of protein methylase II, which catalyzes the transfer of methyl groups from S-adenosylmethionine to carboxyl groups of aspartyl and glutamyl residues in proteins. Enzyme-catalyzed transfer of methyl groups, labeled with 14C or 3H, from S-adenosylmethionine to membrane proteins of McLeod, Ko, and control RBCs was assayed by determining the acceptance of labeled methyl groups under standardized conditions. Membranes of control cells and Ko cells showed about 50 percent greater uptake than did those of McLeod cells. However, when ovalbumin was used as a methyl-accepting substrate, the levels of protein carboxymethyltransferase activity in all three types of cells were found not to differ significantly. In addition, no significant qualitative differences were apparent when methyl-labeled polypeptides from control and McLeod cells were separated by slab gel electrophoresis. The mechanisms responsible for changes in membrane protein methylation of McLeod cells remain unclear. However, these observations provide further evidence of the pleiotropic biochemical lesion associated with the acanthocytic morphology that characterizes McLeod RBCs.
Insights
Red blood cells (RBCs) show altered protein methylation in McLeod syndrome. Membrane protein methylation is reduced in McLeod RBCs compared to control cells, indicating a biochemical abnormality.
Area of Science:
- Biochemistry
- Hematology
- Molecular Biology
Background:
- Red blood cells (RBCs) possess protein methylase II, an enzyme crucial for methyl group transfer.
- This enzyme plays a role in modifying aspartyl and glutamyl residues within proteins.
Purpose of the Study:
- To investigate protein methylation differences in McLeod, Ko, and control RBCs.
- To explore the biochemical basis of McLeod RBC abnormalities.
Main Methods:
- Assaying enzyme-catalyzed methyl group transfer from S-adenosylmethionine to membrane proteins.
- Utilizing radiolabeled methyl groups (14C or 3H) for quantification.
- Employing ovalbumin as a methyl-accepting substrate.
- Analyzing methyl-labeled polypeptides using slab gel electrophoresis.
Main Results:
- McLeod cell membranes exhibited approximately 50% less methyl group uptake compared to control and Ko cells.
- No significant differences in protein carboxymethyltransferase activity were observed when using ovalbumin.
- Slab gel electrophoresis revealed no qualitative differences in methyl-labeled polypeptides between McLeod and control cells.
Conclusions:
- McLeod RBCs display reduced membrane protein methylation, suggesting a specific biochemical defect.
- The exact mechanisms underlying altered methylation in McLeod cells require further investigation.
- These findings support the concept of a pleiotropic biochemical lesion in McLeod RBCs, linked to their acanthocytic morphology.