Protein Ligand Interactions

binding sites

ligands are specific to ___ based on size, shape, hydrophobicity, and charge

Ka

association constant of protein to ligand

1/Ka = Kd

when half of the binding site are occupied, the concentration of ligand is at ___

globins

oxygen carrying proteins: myoglobin and hemoglobin

• consists of eight alpha-helical segments that are connected through bends (globin folds)

myoglobin

monomeric globin that stores oxygen in muscle tissue

hemoglobin

tetrameric globin that transports oxygen into the bloodstream

• subunits are kept together through hydrophobic interactions between amino acid residues

• can exsist in relaxed and tension state

protoporphyrin

group on heme which binds an iron atom which helps transport oxygen

• only iron (II)

heme

protein-bound prosthetic group present in myoglobin and hemoglobin; has iron (II) in its center

Fe²⁺

___ binds to oxygen reversibly

CO

___ binds to heme with 20,000 x greater affinity than O₂ when the heme is not bound to a protein

proximal histidine

histidine residue that stabilizes iron (II)

distal histidine

histidine that makes a bond with oxygen to help it bind to iron (II)

• acts like a gate to let oxygen through

relaxed

when in ___ state, hemoglobin has low affinity for oxygen; in the muscle tissue

coopertivity

oxygen binding to one subunit increases oxygen affinity of others