Hemoglobin and Oxygen Binding

Flashcards covering key vocabulary terms related to hemoglobin, myoglobin, oxygen binding, and allosteric regulation from the lecture notes.

Michaelis Menten Enzymes

Enzymes that possess one active site, producing a hyperbolic saturation curve when substrate concentration is plotted against reaction rate.

Allosteric Enzymes

Enzymes that possess multiple active sites, resulting in a sigmoidal (S-shaped) saturation curve, often exhibiting cooperative binding.

Cooperative Binding

A phenomenon where the binding of one substrate molecule to a multi-subunit protein (like hemoglobin) increases the affinity of subsequent substrate molecules for the remaining active sites.

Hemoglobin

A quaternary protein found in red blood cells that transports oxygen. It consists of four subunits, each with a heme group, and exhibits cooperative binding.

R-state (Relaxed State)

The active conformational state of an allosteric protein, such as hemoglobin, where it has a higher affinity for binding its ligand (e.g., oxygen).

T-state (Tense State)

The inactive conformational state of an allosteric protein, such as hemoglobin, where it has a lower affinity for binding its ligand (e.g., oxygen).

Myoglobin

A simpler oxygen-binding protein with a tertiary structure and a single active site, primarily found in muscle cells. It acts like a Michaelis Menten enzyme and has a higher oxygen affinity than hemoglobin.

Heme Group

A prosthetic group containing an iron atom, centrally coordinated by four nitrogen atoms, which serves as the oxygen-binding site in myoglobin and hemoglobin.

Prosthetic Group

A non-protein component that is tightly bound to a protein and is essential for its biological activity, such as the heme group in hemoglobin.

His F8 (Proximal Histidine)

A specific histidine residue in myoglobin and hemoglobin that covalently binds to the central iron atom of the heme group, anchoring it to the protein within the active site.

His E7 (Distal Histidine)

A specific histidine residue located near the oxygen-binding site in myoglobin and hemoglobin, which helps stabilize the bound oxygen molecule.

Oxyhemoglobin

The form of hemoglobin (or myoglobin) where oxygen is bound to the heme iron, typically associated with the R-state for hemoglobin.

Deoxyhemoglobin

The form of hemoglobin (or myoglobin) where oxygen is not bound to the heme iron, typically associated with the T-state for hemoglobin.

Central Cavity of Hemoglobin

A positively charged pocket located in the center of deoxyhemoglobin (T-state) that closes upon oxygen binding to form oxyhemoglobin (R-state) and serves as a binding site for 2,3-Bisphosphoglycerate (BPG).

Partial Pressure of Oxygen (PO2)

The measure of oxygen concentration when acting as a gaseous substrate, used for hemoglobin and myoglobin, typically expressed in torr.

Fractional Saturation

The proportion of available oxygen-binding sites on a protein (like hemoglobin or myoglobin) that are currently occupied by oxygen molecules, represented on the y-axis of an oxygen dissociation curve.

P50

The partial pressure of oxygen (PO2) at which 50% of the oxygen-binding sites on a protein (like hemoglobin or myoglobin) are saturated. A lower P50 indicates a higher affinity for oxygen.

Oxygen Dissociation Curve Shift to the Right

Indicates a decrease in hemoglobin's affinity for oxygen, meaning oxygen is released more easily to the tissues. This is characterized by a higher P50.

2,3-Bisphosphoglycerate (BPG)

A negatively charged molecule produced in red blood cells that preferentially binds to the positively charged central cavity of deoxyhemoglobin, stabilizing the T-state and lowering hemoglobin's affinity for oxygen, thereby promoting oxygen release to tissues.

BPG and High Altitude

At high altitudes, the body increases BPG production to further decrease hemoglobin's oxygen affinity (shifting the curve to the right), which helps facilitate oxygen delivery to tissues despite the lower atmospheric partial pressure of oxygen.