Myoglobin and Hemoglobin structure

Prosthetic Group

A tight bound non-polypeptide (non-protein) group

What is heme

Heme is a prosthetic group that binds directly to O2

Globins

Globular, mostly alpha helical proteins that use heme to bind to O2

How does heme bind to iron

Fe2+ is bound at six points

Four nitrogens, 1 from the histidine and 1 to the o2

Myglobin function and location

To store oxygen located in muscle cells

Hemoglobin

Carries oxygen from the lungs to the tissue

How does myoglobin bind to Fe2+

Bind to Fe2+ using proximal His which binds directly to Fe2+ and Distal His sits besides the O2 site and controls ligand binding

How does myoglobin reduce hemes preference to bind to Carbon monoxide

Distal histidine has and H-bond with the other oxygen which CO cannot make and the His has a steric clash with CO because CO has triple bond that makes it have an unfavorable angle

General Structure of Hemoglobin

Has four alternating subunits: alpha 1, alpha 2, beta 1, beta 2. Each have their own heme. O2 binding happens in between alternating subunits (beta and alpha)

T state

• State to release O2 in the tissue

• Ions in between subunits that stabilize T state

• Binding of O2 breaks those bonds between subunits and altering the following binding site

• positive cooperative binding