English to Chinese: sample from a textbook General field: Science Detailed field: Biology (-tech,-chem,micro-)
Source text - English Electrophoresis uses a support medium of some type - starch, paper, various types of gels - to both float the mixture and support an electric field. The electric field is engaged for a set amount of time, during which the proteins migrate from the positive end of the field (where the mixtures are placed) to the negative end, depending upon the various charges of the amino acids in each protein (and the interactions with the charged medium). The proteins have been denatured to make them interact better with the medium, as well to shut down the activity of enzymes that could interfere with the process. A protein which is overall more positively charged will migrate farther toward the negative pole during the process. But that's not the only factor that affects how far the protein moves - smaller proteins will pass through the medium faster than large ones. When the process ends and the electric field is turned off, the medium gets stained to make the migrated proteins show up.
This process can be used to isolate proteins for further analysis, as well as to find differences in proteins in two near-identical systems, such as closely-related organisms. It has been used to find differences between normal disease organisms and organisms that have developed drug resistances. If a mutated protein is involved in the resistance, it may be different enough from the normal variety to move to a different place during electrophoresis.
Translation - Chinese 电泳使用某种类型的支持介质（淀粉，纸或各种类型的胶）以承载蛋白混合物并提供电场。在设定的一段时间内施加电场，这期间蛋白从电场的阳极端（即蛋白混合物的上样处）迁移至阴极端。这一过程取决于各蛋白中氨基酸所带的不同电荷（及其与带电介质间的相互作用）。蛋白在上样前已被变性，这样它们能更好地与介质相互作用，同时也抑制了可能影响电泳过程的酶的活性。在电泳过程中，一个整体上带有更多正电荷的蛋白会向阴极端迁移得更远。但这不是影响蛋白迁移距离的唯一因素——小蛋白会比大蛋白更快地穿过介质。当电泳结束，关闭电场，将介质染色以使迁移的蛋白显色。
English to Chinese: sample from an handbook of separation techonologies General field: Science Detailed field: Biology (-tech,-chem,micro-)
Source text - English Analysis and Purification of Proteins and Peptides by Reversed-Phase HPLC
Reversed-Phase High Performance Liquid Chromatography (RP-HPLC) has become a widely used, well-established tool for the analysis and purification of biomolecules. The reason for the central role that RP-HPLC now plays in analyzing and purifying proteins and peptides is Resolution: RP-HPLC is able to separate polypeptides of nearly identical sequences, not only for small peptides such as those obtained through trypsin digestion, but even for much larger proteins. Polypeptides which differ by a single amino acid residue can often be separated by RP-HPLC as illustrated in Figure 1 showing the separation of insulin variants. Insulin variants have molecular weights of around 5,300 Da with only slightly different amino acid sequences, yet most variants can be separated by RP-HPLC. In particular, reversed-phase chromatography is able to separate human and rabbit insulin which only differ by a methylene group—rabbit insulin has a threonine where human insulin has a serine!
The scientific literature has many examples where RP-HPLC has been used to separate similar polypeptides. Insulin-like growth factor with an oxidized methionine has been separated from its non-oxidized analogue and interleukin-2 muteins have been separated from each other. In the latter paper, Kunitani and colleagues proposed that RP-HPLC retention could provide information on the conformation of retained proteins on the reversed-phase surface. They studied thirty interleukin-2 muteins and were able to separate muteins that were nearly identical. Interleukin in which a methionine was oxidized was separated from the native form and in other cases single amino acid substitutions were separated from native forms. They concluded that protein conformation was very important in reversed-phase separations and that RP-HPLC could be used to study protein conformation. In the process they demonstrated the resolving power of the technique for similar polypeptides.
RP-HPLC is used for the separation of peptide fragments from enzymatic digests and for purification of natural and synthetic peptides. Preparative RP-HPLC is frequently used to purify synthetic peptides in milligram and gram quantities. RP-HPLC is used to separate hemoglobin variants, identify grain varieties, study enzyme subunits and research cell functions. RP-HPLC is used to purify micro-quantities of peptides for sequencing and to purify milligram to kilogram quantities of biotechnology-derived polypeptides for therapeutic use.
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