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Defect in 3'-phosphoadenosine 5'-phosphosulfate formation in brachymorphic mice.
Summary
Brachymorphic mice exhibit significantly reduced chondroitin sulfate due to a defect in converting adenosine 5'-phosphosulfate (APS) to 3'-phosphoadenosine 5'-phosphosulfate (PAPS). This is caused by lower APS kinase activity, impacting proteoglycan sulfation.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Proteoglycans are crucial for cartilage structure and function.
- Sulfation of proteoglycans is essential for their biological activity.
- The brachymorphic mouse model exhibits undersulfated proteoglycans.
Purpose of the Study:
- To investigate the biochemical basis for undersulfated proteoglycans in brachymorphic mice.
- To identify the specific enzymatic defect in the sulfate activation pathway.
Main Methods:
- Utilized radiolabeled sulfate (35SO42-) incorporation assays.
- Analyzed extracts from neonatal normal and brachymorphic mouse epiphyseal cartilage.
- Performed specific enzyme activity assays for ATP sulfurylase and APS kinase.
Main Results:
- Brachymorphic cartilage showed significantly lower incorporation of 35SO42- into PAPS (9%) and chondroitin sulfate (13%) compared to normal.
- APS accumulated in brachymorphic cartilage, but overall sulfate incorporation was reduced.
- APS kinase activity was markedly reduced (approx. 1/14) in brachymorphic mice, while ATP sulfurylase was reduced by half.
Conclusions:
- The primary defect in brachymorphic mice is a severely reduced APS kinase activity.
- This enzymatic deficiency impairs the conversion of APS to PAPS, leading to undersulfated proteoglycans.
- The findings pinpoint a critical role for APS kinase in cartilage proteoglycan sulfation.