Scanning isoelectric focusing in small density-gradient columns. I. Use of a standard spectrophotometer cuvette for focusing. Chemical modification of proteins by migrating reactive ions

Isoelectric focusing of plant cell membranes

An isoelectric focusing method is described that discriminates plant cell organelle populations on the basis of surface charge. The isoelectric points (pI values) of the Golgi apparatus, the mitochondria, and putative plasma membrane from etiolated pea stem cells are reported. The pI of the pea Golgi apparatus is similar to that of the (35)SO(4)-labeled membranes of developing Fucus embryos. The pI of Fucus(35)SO(4)-labeled membranes depends on whether the membranes are being polarly transported to the growing tip or randomly transported to the entire periphery of the zygote. Those subject to polar tip transport have a significantly greater negative surface charge than those being randomly transported. The implication of this result toward an understanding of the localization mechanism is discussed. The method is also capable of subfractionating glucan synthetase II-containing membranes (putative plasma membrane) from peas. The pI of putative plasma membrane from a pea stem homogenate is similar to the pI of the plasma membrane of whole protoplasts of Catharanthus leaf cells. Isoelectric focusing appears to be a useful technique to discriminate membranes and, hence, to provide new information and approaches to study cellular and developmental phenomena.

Mass distribution, polydispersity and focusing properties of carrier ampholytes for IEF II: pH 4–6 intervals

For studying the M(r) distribution and number of species in narrow-range (2 pH-unit wide, in the nominal pI 4-6 interval) carrier ampholytes from four commercial sources (Bio-Lyte, Servalyt, Ampholine and Pharmalyte), a 2-D technique was adopted consisting of a focusing step in a liquid phase (Rotofor, yielding 20 fractions) followed by orthogonal CE in both, acidic and basic buffers. As a final step, every other fraction was analyzed by CE-MS. The findings: Ampholine contains 80 different M(r) compounds, in the M(r) interval 203 to 893 Da, for a total of 325 isoforms. Bio-Lyte consists of 66 different M(r) species, in the M(r) range 388 to 835 Da, for a total of 436 isoforms. Servalyt is made of 199 different M(r) compounds, in the M(r) interval 204 to 907 Da, for a total of 1302 isoforms. Pharmalyte pH 4-6.5, comprises 217 amphoteres, in the M(r) range 150 to 1179 Da, for a total of 812 isoforms. Pharmalyte appears to be the best brand, with the vast majority of species focusing sharply at their pI position and <5% "poor" species, distributed along the entire pH gradient, denoting an extremely shallow pH/mobility curve across the pI value.

Theory and practice of isoelectric focusing of interacting systems

The theory of mass transport coupled to reversible protein interactions forms the basis for computer simulation of the isoelectric focusing behavior of several model systems. These include pH-dependent conformational transition, carrier ampholyte-induced interactions and protein-ligand interactions. The computational results compare favorably with experimental observations. In addition, a method is formulated for an isoelectric focusing procedure which enables determination of intrinsic ligand-binding constants for statistical binding of a charged ligand, binding to heterogeneous sites, and cooperative binding.

History of electrophoretic methods

Electrophoresis is the migration of electrically charged particles or ions in solutions due to an applied electric field. The ability to separate very similar substances including different proteins for analytical and preparative purposes has increased, especially since 1950, owing to the introduction of zone electrophoresis in paper and later in gels of polyacrylamide or agarose. After 1960, disc and displacement electrophoresis (isotachophoresis) and isoelectric focusing offered much increased resolution. Electrophoretic methods nowadays promote advances in biochemistry and molecular biology and will continue to be very important in science and for numerous applications in genetics, gene technology, sequencing of nucleic acids and proteins, studies of diseases and malfunctions including cancer, and in the identification of species and individuals, e.g., in forensic medicine.

Isoelectric focusing of the phosphoprotein of rat-incisor dentin in ampholine and acid pH gradients. Evidence for carrier ampholyte-protein complexes

Rat-incisor phosphoprotein (RIP) has been subjected to isoelectric focusing at 4 degrees in (a) an Ampholine pH gradient of 2.5-4 and (b) an acid pH gradient created by electrolysis of a system of acids and acidic ampholytes and covering the pH range 0.5-3.5. In the Ampholine gradient, the RIP unexpectedly formed several adjacent and strongly opalescent bands in the pH range 2.5-3.1. These bands, which migrated slowly toward the anode on prolonged focusing, are interpreted as being the result of an interaction between the amino groups of the Ampholine and the numerous phosphate groups of the protein. In the acid pH gradient, the RIP focused into one narrow zone corresponding to an isoelectric pH of 1.1 at 4 degrees. This value is consistent with the amino-acid composition and the phosphate content of the protein,

Scanning isoelectric focusing in small density-gradient columns. IV. The use of deuterium oxide for preparing the density gradient and its effects on isoelectric points of proteins

The use of deuterium oxide as a substitute for sucrose in preparing density gradients for small isoelectrofocusing columns has been investigated. A density gradient was created directly in a 1.5-ml column by free inter-diffusion of three deuterium oxide solutions for 3 min. The resulting deuterium oxide concentration course (as shown by measurement of the refractive-index gradient) had a very high degree of linearity. Test runs with beta-lactoglobulin and sperm-whale myoglobin showed that the strength and stability of the deuterium oxide density gradient should normally be sufficient for stabilization of protein zones against convection during isoelectric focusing. The isoelectric points of beta-lactoglobulins A and B were found to increase as the concentration ratio of deuterium oxide to water at focusing level increased. Within the limits of experimental error, the pI shift corresponding to a given change in solvent composition was equal for both components. These findings are accounted for in terms of the deuterium isotope effect on the dissociation constants of protolytic groups and the shift in the asymmetry potential of the glass electrode in deuterium oxide as compared with water. The spontaneous reduction of sperm-whale metmyoglobin to ferrous myoglobin, which occurs on prolonged isoelectric focusing, is discussed, as are the benefits and drawbacks of deuterium oxide as a density-gradient solute.