Two-dimensional polyacrylamide gel electrophoresis of membrane proteins

Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) is one of the most powerful separation techniques for complex protein solutions. The proteins are first separated according to their isoelectric point, driven by an electric field across a pH gradient. The pH gradient necessary for the separation according to isoelectric point (pL) is usually established by electrophoresing carrier ampholytes prior to and/or concomitantly with the sample. The second dimension is usually a separation according to molecular size. Mostly this separation is performed after complete denaturation of the proteins by sodium dodecyl sulfate and 2-mercaptoethanol (SDS-PAGE). This standard method has considerable disadvantages when relatively hydrophobic membrane proteins are to be separated: cathodic drift, resulting in nonreproducible separation, and the denaturation of the protein, mostly making it impossible to detect native properties of the proteins after separation (e.g., enzymatic activity, antigenicity, intact multimers, and so on). The protocols presented here take care of most of these obstacles. However, there is probably no universal procedure that can guarantee success at first try for any mixture of membrane proteins; some experimentation will be necessary for optimization. Two procedures are each presented: a denaturing (with urea) and a nondenaturing method for IEF in immobilized pH gradient gels using Immobilines, and a denaturing (with SDS and 2-mercaptoethanol) and a nondenaturing technique (with CHAPS) for the second dimension. Essential tips and tricks are presented to keep frustrations of the newcomer at a low level.     

Characterization of fish acid proteases by substrate–gel electrophoresis

Several analytical techniques based upon the use of substrate–polyacrylamide gel electrophoresis were evaluated to achieve characterization of aspartate proteases in fish stomach. Since aspartate proteases of fish are more stable at high pH than mammalian pepsins, the most accurate technique for activity assessment is electrophoresis at neutral pH and revealing of such activity at low pH with hemoglobin as substrate. The technique is suitable for characterization of proteases and in comparative assessment of acid protease activity in different sparids.     

Comparison of spiroplasmas by polyacrylamide gel electrophoresis of cell proteins

Pseudomonas oxalaticus utilized sodium acetate or fructose, in addition to sodium formate known to be assimilated via the reductive pentose phosphate pathway. The generation time during growth on fructose (2 h, 10 min) was considerably shorter than observed for other pseudomonads, which sequentially utilize a phosphoenolpyruvate-dependent phosphotransferase system and 1-phosphofructoninase during growth on fructose. In contrast, extracts prepared from fructose-grownP. oxalaticus contaned enzyme activities indicative of the Entner-Doudoroff pathway, while 1-phosphofructokinase was not found. Our studies indicate thatP. oxalaticus may be useful as a model organism for studies of CO₂ fixation.     

Determination of Triton X-100 binding to membrane proteins by polyacrylamide gel electrophoresis

The molecular weight of proteins in protein-detergent complexes can be determined from ultracentrifugation experiments if the amount of bound detergent is known. A new sensitive method to measure the binding of the nonionic detergent Triton X-100 to proteins has been developed. For the membrane proteins studied, less than 50 μg of protein was required to achieve an accuracy of 10% in the determination of the detergent-protein weight ratio.The proteins were equilibrated with the detergent by electrophoresis into polyacrylamide gels containing radioactively labelled Triton X-100. The gels were then sliced and the amount of bound detergent calculated from the increase in radioactivity in the slices containing the protein zone. The amounts of protein were determined by amino acid analysis of identical protein zones cut from gels running parallel .     

Separation of rat liver lysosome membrane adenosine triphosphatase activities by polyacrylamide gel electrophoresis

Solubilization of rat liver lysosome membranes with octyl glucoside or lauryl sarcosinate and analysis of ATPase activities in sections of polyacrylamide gels after electrophoresis revealed one major peak at pH 8 and two peaks at pH 5. The pH 8 ATPase peak was not localized in the same peak with pH 5 ATPase activity, suggesting that these were catalyzed by different proteins. Ca2+- and Mg2+-ATPase activities at pH 8 were present in the same major peak, with Ca2+ activity predominating. The pH 8 Ca2+-ATPase was also not present in the same area of the gels as Ca2+-ADPase.     

Structural analysis of glycopeptides by polyacrylamide gel electrophoresis

Three different well-characterized preparations of proteoglycan subunits were analyzed by high-performance liquid chromatography on a silica-based material bonded with an amide phase. The biochemical integrity of the proteoglycan subunits was retained during this procedure. The high sensitivity coupled with the increased speed of high-performance liquid chromatography will permit rapid analysis and comparisons of very small specimens.     

Separation of aminoacyl-transfer RNAs by polyacrylamide gel electrophoresis

A polyacrylamide gel electrophoresis system for separating $\text{E.}$$\text{coli}$ tRNAs and aminoacyl-tRNAs is described. The tRNA was separated into 6 discrete bands which contained varyin aamounts of tRNA and therefore varying numbers of tRNA species. In order to locate specific tRNAs, tRNA was charged with a ¹⁴C amino acid and the aminoacyl-tRNA was located by autoradiography. With several amino acids, 2 isoaccepting species were found. In total, 30 aminoacyl-tRNAs were located.     

Separation of t-RNAs by two-dimensional polyacrylamide gel electrophoresis

A pH 5.8 polyacrylamide gel electrophoresis buffer is described. Electrophoresis in this MES-citrate system at pH 5.8 separates E. coli transfer RNAs into 15 bands using 15% acrylamide gels. Polyacrylamide gel electrophoresis in a second dimension at pH 8.3 further resolves E. coli t-RNAs into 20 spots.