87.ACONITASE WHICH ACTS IN CONVERSION OF CITRATE TO ISOCITRATE CONTAINS
A.IRON
B.MAGANESE
C.ZINC
D.CALCIUM
ANS:IRON
The cytosolic form of aconitase also acts as iron regulatory protein 1. The lower structure, from PDB entry 2ipy, shows how it performs this entirely different function. The iron-sulfur cluster in aconitase is unstable and must be replaced occasionally when it falls out. When iron levels in the cell get low, there isn't enough iron to regenerate the cluster, and the protein shifts to its second function. The protein opens up and grips hairpin loops in a few specific messenger RNA molecules. These include a hairpin at the start of the messenger RNA for ferritin, and five similar hairpins at the end of messenger RNA for the transferrin receptor. When the iron regulatory protein 1 binds, it inhibits the formation of ferritin, so that less iron is locked up in storage, and it enhances construction of the transferrin receptor, so the cell can pick up more transferrin out of the blood, and with it, more iron.
A.IRON
B.MAGANESE
C.ZINC
D.CALCIUM
ANS:IRON
The cytosolic form of aconitase also acts as iron regulatory protein 1. The lower structure, from PDB entry 2ipy, shows how it performs this entirely different function. The iron-sulfur cluster in aconitase is unstable and must be replaced occasionally when it falls out. When iron levels in the cell get low, there isn't enough iron to regenerate the cluster, and the protein shifts to its second function. The protein opens up and grips hairpin loops in a few specific messenger RNA molecules. These include a hairpin at the start of the messenger RNA for ferritin, and five similar hairpins at the end of messenger RNA for the transferrin receptor. When the iron regulatory protein 1 binds, it inhibits the formation of ferritin, so that less iron is locked up in storage, and it enhances construction of the transferrin receptor, so the cell can pick up more transferrin out of the blood, and with it, more iron.
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