The separation, partial purification and some properties of isoenzymes of aldolase from guinea-pig cerebral cortex

1. Aldolase isoenzymes from guinea-pig cerebral cortex were partially purified and separated by ammonium sulphate fractionation and chromatography on DEAE-cellulose. 2. Each purified isoenzyme was shown to be virtually uncontaminated with other forms by starch-gel electrophoresis. The quantitative distribution of the isoenzymes was: I, 6·2%; II, 5·2%; III, 15·3%; IV, 25·7%; V, 33·3%. 3. The pH optima for the five separated isoenzymes were similar; all were in the range pH7·5–8·0. Values for pK_a (6·31–6·55) and pK_b (9·45–9·59) were calculated from the data and suggested the involvement of histidine and lysine residues. 4. The stabilities of the isoenzymes were shown to be I=II>III>IV>V at pH4·4 in order of decreasing stability and are discussed in terms of subunit structure. 5. The substrate activity ratios (fructose 1,6-diphosphate/fructose 1-phosphate) were measured and all were in the range 12–44.