BIOC 503 - Protein Functions II

transition metal

protein side chains lack affinity for O2, so it uses some ___ ions

free radicals

transition metal ions would create ___ if left free in solution, which is toxic for the cell at high doses.

protein-bound

myoglobin (storage) and hemoglobin (transport) can bind oxygen via ____ heme group.

tetramer

hemoglobin (Hb) is a ___ of 2 subunits: alpha2 & beta 2

subunit composition of hemoglobin

• 2 alpha2 subunits

• 2 beta2 subunits

myoglobin

each hemoglobin subunit is structurally similar to ____

30

myoglobin and hemoglobin have some sequential similarity, about __%, but sequential similarity is relatively subjective.

porphyrin

heme group consists of multiple organic ring structures, including ___ rings which are made of 4 pyrrole rings linked by methene bridges.

6, 4, 2

when bound, the iron ion has __ coordination bonds: __ in the plane/bonded to porphyrin ring system, and __ perpendicular to it.

5, 6

heme is mainly bound to helical segments __ and __ of myoglobin

chromophore

the heme group is a strong ___ which allow the monitoring of O2 binding through UV-vis spectrometry

429

ferrous form (Fe2+) without oxygen shows absorbance at ___nm

414

ferrous form (Fe2+) BOUND TP oxygen shows absorbance at ___nm

high

myoglobin could not transport oxygen because its affinity for it is still too ___ in the muscle tissues and its corresponding O2 concentration.

• it will lot release it because the O2 concentration in muscles is still high enough for it to be saturated

sigmoidal

A ___ binding curve indicates positive cooperativity, and shows that hemoglobin affinity for O2 changes based on O2 concentration

cooperativity

a protein has to have multiple binding sites that are able to interact with each other

positive cooperativity

first binding event increases affinity at remaining sites

• recognized by sigmoidal binding curve

• hemoglobin and O2

negative cooperativity

first binding event reduces affinity at remaining sites

• not sure it exists as not found in nature

7.5

1 kPa = ___ Torr

Hill coefficient

number that is theoretically the number of binding site, but is practically described as the degree of cooperativity

• n

no cooperativity

n = 1

positive cooperativity

n >1

negative cooperativity

n < 1

concerted cooperativity model

enzyme subunits are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits.

sequential cooperativity model

subunits are not connected in such a way that a conformational change in one induces a similar change in the others. Thus, all enzyme subunits do not necessitate the same conformation. - -

• Moreover, the sequential model dictates that molecules of substrate bind via an induced fit protocol.

• very large number of possible conformations since all subunits DO NOT change all at once

allosteric regulation

binding of a ligand to one site affects the binding properties of a different site on the same protein

• can be positive or negative

• can be homotropic or heterotopic

homotropic

the normal ligand of the protein IS the allosteric regulator

• example: O2 binding to hemoglobin makes more binding more favorable

heterotropic

a different ligand affects the binding of the normal ligand

positive, homotropic

cooperation = __ __ regulation