Glutamine isoelectric point

The purification of glutamine cyclotransferase from papaya latex has been carried out by Messer and Ottesen (116). A batch procedure was used for the removal of impurities by passage of a papaya latex extract through a thin layer of carboxymethyl-Sephadex the active protein was separated by selective elution. Additional purification was achieved by chromatography on a column of carboxymethyl-Sephadex and by gel filtration on Sephadex G-100. The purified enzyme was homogeneous by the criteria of paper electrophoresis, ultracentrifugation, and gel filtration on Sephadex G-100 columns and chromatography on carboxy-methyl- or DEAE-Sephadex. The electrophoretic behavior of the enzyme indicates that it is a basic protein with an isoelectric point near... 

Wedler f al. (1978) have identified two forms of glutamine synthetase in Bacillus caldolytiens and Darrow and Knotts (1977) have shown two forms in Rhizobium japonicum and other free living root nodule bacteria. In both cases the two forms differ in their isoelectric points and stability. The work of Darrow and Knotts (1977) indicates that the two forms are not the result of differences in adenylation state of a single form. Type I appears similar to the E. coli enzyme in stability and in being susceptible to adenylation. Type II however is not adenylated and is more unstable. 

Account for the fact that the isoelectric point of glutamine (pi 5.65) is higher than the isoelectric point of glutamic acid (pi 3.08). 

Major changes in phosphorylation induced by ischaemia and subsequent reperfusion in rat striatum were observed for a 130-kDa protein, tentatively identified as the Ca "" transport ATPase, and calcium/calmodulin-dependent protein kinase II (Sankaran etal. 1997). A 200-300% increase in [ PjSNjATP photoinsertions was observed in the striatum and hippocampus region of a 43-kDa protein with an isoelectric point of 6.8. This protein was identified as glutamine synthetase and the increase in binding was found to be due to both increased copy number and activation by Mn ". An increase in [ PjSNjATP photoinsertions into a 55-kDa protein, identified as the P-subunit of tubulin, was found only in the striatum and hippocampus indicating the depolymerization of microtubulin in these tissues. 

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