Molecular forms of red blood cell hexokinase

Abstract

Mammalian red blood cell hexokinase has been shown to exist in two or more distinct molecular forms, which are separable by ion-exchange chromatography. Of these forms just one corresponds to hexokinase type I from other tissues, while the others differ from any previously reported hexokinase isozyme. Analysis of several molecular properties of the three major forms (Ia, Ib and Ic in the order of their elution from DE-52 columns) of hexokinase prepared from human red cells and of the two forms purified from rabbit reticulocytes, shows significant differences in the isoelectric point. The kinetic and regulatory characteristics, the molecular weight, the temperature and pH-dependence of the various isozymes were similar. The hexokinase isozymic pattern is largely dependent upon red blood cell age. Among all, hexokinase Ib is the predominant form in rabbit reticulocytes and becomes the minor component in the older cells; a similar situation has also been found in the human erythrocyte. At present the molecular basis of hexokinase heterogeneity remains unknown, however preliminary experimental findings indicate a post-translational modification as a possible mechanism.

Human erythrocyte hexokinase deficiency: a new variant with abnormal kinetic properties

“…It is well known that HK activity strictly depends on the red blood cell age (Magnani et al, 1979;Stocchi et al, 1982). Fig 2 shows that, in the patient, lower HK levels were found in all red blood cell fractions separated according to their age by density gradient ultracentrifugation (Turner et al, 1974) and that the decay rate of the proband's HK was similar to that of normal controls.…”

“…Ked blood cell hexokinase is of central importance for erythrocyte metabolism (Brewer, 1974). This enzyme is markedly modulated by many glycolytic intermediates (Stocchi et al, 1982;Magnani et al, 1981;Ninfali et ul, 1980) and, among all glycolytic enzymes, it shows the fastest decay during cell ageing (Seaman et al, 1980). In the human erythrocyte it is present in multiple forms all of which are sub-types of HK I (Fornaini et al, 1982).…”

“…Human red blood cell hexokinase has been shown to exist in multiple molecular forms (in the type I hexokinase area) which are separable by ion-exchange chromatography (Stocchi et al, 1982). Chromatography of the patient's HK showed the same pattern of normal controls but all forms of the enzyme were present at a lower leveI (Fig 1).…”

“…All other glycolytic enzymes assayed were normal or slightly increased (pyruvate kinase and glucose-&phosphate dehydrogenase). Since these last two enzymes are known to be cell age-dependent (Brewer, 19 74), and taking into account that among glycolytic enzymes HK is the most prominently affected by the cell age (Magnani et al, 1979;Stocchi et al, 1982). we must conclude that red cells from the proband do not contain more than 30-40% of expected HK .…”

“…7 ml were collected and assayed for HK activity. Further details of the method are reported in Stocchi et al (1982).…”