![]() ![]() ![]() I like to visually think of solutions as being a sort of “ proton cookie jar” and the pH reflects the fullness of that jar. Gaining a proton (protonation) can positivize a neutral or neutralize a negative whereas losing a proton can negativize a neutral or neutralize a positive. Some amino acids are able to give protons (act as acids) or take protons, (act as bases) depending on the proton availability, and since those protons are positively-charged, give/take-ing them changes the protein’s charge. And the 2 are directly related – pH is a measure of how many protons (H⁺) are in a solution – it’s an inverse log, so the more H⁺ (more acidic), the lower the pH. Whether, in which direction, and to what extent, a protein is charged depends on “how it’s spelled” (what protein letters (amino acids) does it have in what order?) and what the pH is. I always had a problem remembering the terminology, but when it comes to ion exchange chromatography – the flavors refer to the type of ion that’s being exchanged – NOT the one that the resin – so anion exchange chromatography uses positively-charged resin to bind negatively-charged ( anionic) proteins – and cation exchange chromatography uses negatively-charged resin to bind positively-charged ( cationic) proteins. ![]() So if your protein’s -charged (we call this cationic) you’ll want – charged resin (like an S column) but if your protein’s -charged (we call this anionic) you’ll want charged resin (like a Q column). But in order for the protein to stick to the resin in the first place, that resin needs to be oppositely-charged compared to the overall protein. the Na⁺ can compete off, thus exchanging for, a positive protein and the Cl⁻ can compete off a negative protein). So if you gradually increase the salt you can push proteins off based on their charge, separating them in the process.īecause of that whole “positive part AND negative part,” a salt can be used to unstick either a negatively-charged ( anionic) OR a positively-charged ( cationic) protein (e.g. The more opposite the protein
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |