Which LD isoenzymes decrease when stored at 4°C?

Which LD isoenzymes decrease when stored at 4°C?

• A. LD1-3
• B. LD4-5
• C. LD6-7
• D. LD3-4

Answer: (B)

Enzyme stability varies among isoforms, and storage temperature can differentially affect their activity. Lactate dehydrogenase isoenzymes are tetramers made from H and M subunits, and LD4 and LD5 have a higher content of M subunits, which makes their quaternary structure more prone to destabilization at 4°C. Because activity assays rely on intact, active tetramers, this greater instability leads to a larger loss of LD4 and LD5 activity when samples are stored at 4°C. LD1 and LD2 tend to be more stable under these conditions, with LD3 intermediate in stability, so their activities are less affected. To maintain the accurate LD isoenzyme pattern, samples are often stored at freezing temperatures or aliquoted to minimize degradation, avoiding repeated freeze-thaw cycles.

Enzyme stability varies among isoforms, and storage temperature can differentially affect their activity. Lactate dehydrogenase isoenzymes are tetramers made from H and M subunits, and LD4 and LD5 have a higher content of M subunits, which makes their quaternary structure more prone to destabilization at 4°C. Because activity assays rely on intact, active tetramers, this greater instability leads to a larger loss of LD4 and LD5 activity when samples are stored at 4°C. LD1 and LD2 tend to be more stable under these conditions, with LD3 intermediate in stability, so their activities are less affected. To maintain the accurate LD isoenzyme pattern, samples are often stored at freezing temperatures or aliquoted to minimize degradation, avoiding repeated freeze-thaw cycles.