Answer:
α₄β₄ hetero-octamer
Step-by-step explanation:
The quaternary structure of proteins describes the arrangement of two or more polypeptide subunits in the space. According to the given information, the enzyme phosphofructokinase-1 (PFK-1) has two different types of subunits namely alpha and beta subunits. A protein with two or more different types of the subunit is said to be hetero-polymer.
There are four alpha subunits and four beta subunits in the protein PFK-1 making a total of 8 subunits. A protein with eight subunits is said to be an octamer. Therefore, the quaternary structure of PFK-1 would include an arrangement of 4 alpha and 4 beta subunits in space.