Quatenary Structure

Some enzyme proteins are made up of two or more subunits that bind together to produce the functional enzyme. This quaternary structure determines the number of electrophoretic bands expected in heterozygote individuals.

Monomeric proteins – one subunit

Heterozygotes show two bands, one for each allozyme.

Dimeric proteins – two subunits

Heterozygotes shows three bands, one for each FF or SS allozyme dimer and one for the FS dimer. This heterodimer is expected to have an intermediate mobility between F and S. The dimer combinations will occur in a 1:2:1 ratio, thus the middle band should be most intense.

Gels:

1. Monomeric enzyme protein (PGM): two heterozygotes FS and MS:

2. Dimeric enzyme protein (PGI): SF, SS, SF

3. Triploid pattern (3 allozymes: S, M, F) in a monomeric enzyme (PGM)

Exercise:

Use ImageJ to quantify variation in banding intensity among allozyme bands for the three gels shown above.

Click HERE to start the exercise.