Characteristics of galactokinase and galactose-1-phosphate uridyltransferase in cultivated fibroblasts and amniotic fluid cells

Culture of galactosaemic fibroblasts in the presence of galactose: effect of inosine

Fibroblasts from three galactosaemics had no galactose-1-phosphate uridyltransferase (GALT) activity. These fibroblasts cells were cultured in different media supplemented with dialysed fetal calf serum. Galactosaemic and control cell strains stopped growing in hexose-free medium. In glucose-free medium containing galactose, galatosaemic cells, in contrast to control cells, stopped growing after two days and died. In the same medium supplemented with inosine, they exhibited the same growth pattern as the control cell strains although in the presence of high concentrations of galactose-1-phosphate (Gal-1-P). These findings indicated that the glucose-free medium containing galactose supplemented with dialysed fetal calf serum and inosine, as a ribose donor, was appropriate for further in vitro investigations of galactose metabolism in galactosaemic cells.

Cytosolic thymidine kinase activity in cultured human fibroblasts from individuals with galactokinase deficiency

The structural genes for human galactokinase (GALK) and the human cytosolic form of thymidine kinase (TK1) are located on 17q21-q22. These two loci are tightly linked, and studies on Chinese hamster cell lines have shown that the expression of TK1 and GALK genes may alter simultaneously. We investigated the possibility of a dependent mutation of TK1 and GALK genes in cultured fibroblasts, obtained from two patients homozygous for the GALKG-deficient gene. Since we showed that the TK1 level varies as a function of the passage and the growth rate of a given strain, our experiments were performed on nonstored skin fibroblasts, between the third and the fifth passage for both controls and patients. We found that TK1 levels in GALK-deficient cells were almost 75% of those observed in control strains with a similar growth rate. Previous results in the literature have shown a pronounced decrease in TK1 activity in three GALK-deficient fibroblastic strains. We suggest that these disparities of TK1 levels in GALK-deficient fibroblasts may be related either to genetic heterogeneity of GALK deficiency or to differences in culture conditions.

Diagnosis of Pompe's disease using leukocyte preparations. Kinetic and immunological studies of 1,4-alpha-glucosidase in human fetal and adult tissues and cultured cells

Kinetic and immunological studies of 1,4-alpha-glucosidase show that the distribution of acid, renal and neutral alpha-glucosidase at pH 4.0 and 6.5 is as follows: in liver and cultured fibroblasts and amniotic fluid cells the activity at pH 4.0 is mainly due to the acid enzyme. Even at pH 6.5, the activity is largely due to the residual activity of the acid enzyme. In kidney and leukocytes, however, the activity by acid enzyme at pH 4.0 represents only 30-60% of the total activity and the remaining activity is from renal enzyme. At pH 6.5, the activity is almost exclusively of renal enzyme. Renal alpha-glucosidase has a higher affinity for maltose (Km, 0.8 mmol/l) than acid enzyme, however; for glycogen acid enzyme shows the highest affinity (20.7 g/l). There is no significant difference in the kinetic characteristics of alpha-glucosidase between fetal and adult tissues. In kidney, however, a relative increase in renal enzyme to acid enzyme with age is found, i.e. in fetal kidney the alpha-glucosidase activity at pH 4.0 is more than twice that at pH 6.5, whereas in adult kidney, the activity ratio at pH 4.0-6.5 is approximately 1. Antibodies for human liver acid alpha-glucosidase decrease the alpha-glucosidase activity in normal leukocytes by 22-75% at pH 4.0 (0.54-3.8 nmol/min per mg protein). The decrease is significantly lower in patients with Pompe's disease (0-0.11 nmol/min per mg protein) as well as in their parents and some siblings (0.15-0.70).

Prenatal diagnosis of galactosemia and properties of galactose-1-phosphate uridyltransferase in erythrocytes of galactosemic variants as well as in human fetal and adult organs

The kinetic characteristics and isoelectrofocusing patterns of uridyltransferase and the concentrations of galactose-1-phosphate in hemolysates were investigated in a family with compound variants of Duarte and classical galactosemia. There were no significant differences in Km values between the genotypes. However, the isoelectrofocusing study with thin-layer polyacrylamide gels (PAGIF) as well as with agarose gels (AGIF) showed a distinctive difference. The enzyme from the Duarte variant resolved into at least two more activity bands at pH between 5.2 and 5.4. The accumulation of galactose-1-phosphate was observed only in homozygotes for classical galactosemia. Compound heterozygotes (G-D) without any clinical manifestations did not show an accumulation of galactose-1-phosphate. The isoelectrofocusing study of the enzyme in human tissues revealed their activity resolving into multiple bands, 6-8 bands at pH 5.50-6.00 and 1-3 bands at pH 4.9-5.2. No significant differences were found in the patterns between fetal and adult liver except that the intensity of the anodic bands (pH 4.9-5.2) was weaker in fetal tissues. Prenatal diagnosis of classical galactosemia was performed in nine families by measuring the enzyme activity in cultivated amniotic fluid cells. Absence of the enzyme activity in amniotic fluid cells was found in two cases, and in four cases the heterozygosity was diagnosed by a relative low enzyme activity, 30-50% of the activity in control cells cultured in parallel.

Characterization of galactose-1-phosphate uridyl-transferase and galactokinase in human organs from the fetus and adult

Some properties of galactose-1-phosphate uridyltransferase (EC 2.7.7.12) and galactokinase (EC 2.7.1.6) were investigated in human organs, i.e., in liver kidney, skeletal muscle, lung, spleen, heart and brain from fetuses as well as liver, kidney and skeletal muscle tissues from adults. (1) Galactose-1-phosphate uridyltransferase (transferase) is quite stable when stored below 4 degrees C, and can be frozen from a couple of months without noticeable loss of activity. Galactokinase is relatively stable as long as the cell structure is intact. In cell homogenates its activity decreases very fast, especially under freezing conditions. (2) The pH optimum of transferase in all human tissues is at pH values between 8.2 and 8.4 except in erythrocytes in which it is at a higher pH value. Maximal activity of galactokinase is observed at approximately 8.2 in all human tissues. (3) The Km values of transferase are similar in all human organs, and the values in fetal tissues are not significantly different from those in adult tissues. In the case of galactokinase also no distinct tissue variations are observed in Km values. However, galactokinase affinity for both substrates is considerably higher in adult organs than in fetal organs. (4) Transferase and galactokinase activity in human liver is resolved into two major components on DEAE-cellulose columns. It seems that transferase and galactokinase exist in human tissues as more than two isoenzyme constituents.

Purification and characterization of human erythrocyte uridylyl transferase

A new method for the purification of human erythrocyte uridylyl transferase (UDPglucose: alpha-D-galactose-1-phosphate uridylyltransferase EC 2.7.7.12) is described. It consists of a hydrophobic purification step associated with hydroxyapatite chromatography and provided for the first time a purification of more than 45 000-fold with a high activity (15 I.U/mg) and a yield of 32%. We show that the enzyme is a dimer and has a molecular weight of 88 000. It can be resolved into three bands by isoelectric focusing with an apparent pI between 5.0 and 5.4. It could be shown by steady-state initial rate measurements that the interconversion of the two substrates of human transferase (Gal-1-P and UDP-glucose) follows ping-pong bi-bi kinetics, with Km values of 0.2 and 0.065 mM, respectively.