Question

you are purifying enzyme Z. You think that the preparation is not pure, based on the following data (choose all correct answers):

Group of answer choices

there are three bands on an SDS-PAGE gel

there is only one band on a native PAGE gel

there are two bands on an IEF gel

Answer 1

first and third statements are correct- both the statements signify that enzyme preparation is not pure (more than one protein samples are present)

SDS- PAGE resolves or separates different proteins (enzymes) on the basis of molecular weights. If there are three bands on SDS PAGE gel then it means that proteins of three different molecular weight are present in the enzyme preparation and hence, the preparation is not pure.

Proteins are separated on the IEF (iso electric focussing) gel on the basis of their iso electric points (pI value). This technique focusses on the fact that total charge on the protein is dependent upon surrounding pH. During iso electric focussing proteins moves towards anode or cathode depending on the basis of their net charge till it reaches in the pH range which is equivalent to it's iso electric point.

Presence of two bands in IEF gel indicates that there are at least two proteins with different iso electric points. Hence, the enzyme preparation is not pure in this case as well.

2nd statement is incorrect in the context of impure enzyme preparation. Presence of single band in native page means the enzyme preparation is pure. Hence, this option is incorrect.