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

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Abstract
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 pKa (6·31–6·55) and pKb (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.