Hi Lex

In this case, it is the same Ab in both form: conjugate and unconjugate, therefore it has the same specificity. If you use the Ab HRP conjugate your WB assay will be faster that if you use unconjugate Ab, because you only have to add sustrate affter Ab conjugate incubation. The use of primary Ab unconjugate and after a secondary Ab conjugate requiere an additional incubation step. With the use of a double Ab system (primary and secondary conjugate) you may have greater sensitivity but may also increase the risk of nonspecific reactions (background). I would first try the conjugated Ab.

Regards, Oscar

HRP is the peroxidase enzyme responsible for releasing chemiluminescence during the detection of your western blot (if you are using the conventional POD substrate method).

Oscar already nicely described the difference between the two antibodies you listed. You can either have the HRP conjugated to the primary antibody or usually you have a secondary HRP-carrying antibody directed against the species of the primary AB.

You said that you already have a suitable secondary antibody, so I would actually suggest that you get the unconjugated primary. Since it is not HRP-conjugated, you will be able to use the primary antibody in a variety of other experiments if the need arises. Getting the HRP-conjugated primary will needlessly restrict the use of this antibody for future experiments.

Good Luck!