Increased activity of a basic LDH 5-related isoenzyme in cells derived from chronic myeloid leukemia

The LDH isoenzyme pattern in cells derived from patients (n = 24) with chronic myeloid leukemia (CML) was studied using a high resolution isoelectric focusing (IEF) technique. In K562 cells a highly basic (band B, IEP greater than 10.5) LDH isoenzyme was detected. Using a 2-dimensional technique combining electrophoresis and IEF, its relation to the LDH 5 isoenzyme was demonstrated. From its heat-stability it is concluded that band B is composed of 4 M subunits. The activity of the basic band correlated with the number of CML blast cells and was absent in juvenile, band and segmented neutrophils. Our observations are compatible with a gradual loss of activity during myeloid differentiation. The nature of band B remains unclear, but artefacts due to ligand (lactate, pyruvate, NAD+) binding were ruled out.