Immunological specificity of the isoenzymes I and III of human hexokinase (ATP:D-hexose 6-phosphotransferase EC 2.7.1.1) Estimation of isoenzyme pattern by quantitative immunotechniques☆

The immunological relationship of hexokinase isoenzymes I and III from human tissues was tested with antisera made against purified forms of these enzymes. There was no evidence for crossreactivity as tested by immunoinhibition and precipitin experiments. In mixtures of the two hexokinases made from stock solutions the relative concentration of each form could be determined by specific precipitation with the homologous antiserum. When the method is applied to extracts from human tissues high concentrations of hexokinase form III were found in liver (more than 50% of total hexokinase activity), spleen (up to 50%) and lung (below 20%). From the immunological data it is concluded that the low Km hexokinases from mammalian tissues constitute a family of distinct proteins with similar catalytic properties. The general applicability of immunoinhibition methods for the evaluation of the tissue concentrations of the hexokinase isoenzymes is discussed.