It's simply a combination of two different types of protein purification techniques. So in twodimensional gel electrophoresis, we take our mixture of proteins and we first expose it to isoelectrofocusing. We separate the proteins based on their isoelectric point. So the PH value at which that particular protein basically has a net charge of zero. And after that, we expose that solution, that mixture of proteins, to the process of SDS polyacrylamide gel electrophoresis, also known as SDS Page. So P is the first letter.