[Study of hereditary fructose intolerance by methods of molecular biology]. / Etude de l'intolérance héréditaire au fructose par les méthodes de la biologie moléculaire.

Fructose intolerance is caused by a deficit of the liver aldolase B enzyme. Its molecular mechanisms were studied at different sites: The protein was studied by a method combining electrophoresis, transfer and immunology. It was present in the 15 cases examined. The genetic variability was demonstrated by the quantitative differences of the immunoreactive proteins. Aldolase messenger RNA was prepared and used to direct in vitro synthesis of human aldolase. Cloning complementary DNA of human aldolase was achieved by using the messenger RNA. Two clones were prepared. The aldolase B gene was then analysed using restriction enzymes in 60 control subjects and 11 patients. An abnormality of the DNA was demonstrated in one of the patients and in her father.

Molecular studies on galactose 1 phosphate uridylyl transferase from normal and mutant subjects. An immunological approach.

The mutant forms of uridylyl transferase of eight galactosemic patients and two 'Rennes' variants were characterized with regard to the presence and level of immunoreactive protein, the apparent subunit molecular weight and the isoelectric point. Semi-purified haemolysates were studied by various electrophoretic techniques, then proteins were electrophoretically transferred on to nitrocellulose filters. They were treated with specific anti-transferase antibodies, and then with radioiodinated protein A, followed by autoradiography. We have found that: in all cases, a cross-reacting material was detectable, with a molecular subunit size of 46 000, indistinguishable from that of controls. a biochemical heterogeneity of the mutant enzyme was found: the amount of apparent immunologically reactive protein varied from 20 to 100% of that of controls; electrophoretic experiments performed on two 'Rennes' variants showed an increased negative charge.

Pyridoxal 5' phosphate involvement in age-related modifications of tyrosine aminotransferase: multiple form patterns.

Multiple form patterns of tyrosine aminotransferase were studied in senescent and adult rat liver. Two main modifications were described for "old" rat enzyme: (i) appearance of a new molecular form, specific for old rats, eluted after adult form III and having other properties identical to this form; (ii) disappearance of intermediate forms II and III after enzyme induction; this result seems to be due to acceleration of the conversion process. Vitamin B6 deficiency of old rats explain this and other (previously described) post-translational modifications of "old" tyrosine aminotransferase. The influence of pyridoxal 5' phosphate and the role of protease(s) in the multiple form conversion are discussed. Moreover we show the possibility of a correlation between in vivo alterations of the enzyme molecule and modifications of tyrosine aminotransferase multiple form patterns observed in vitro.

DNA methylation and gene expression.

In the field of studies of the mechanisms of gene expression, much recent work using the methods of genetic engineering, have suggested the hypothesis of a role of DNA methylation (on some cytosines) in the control of gene activity. Undermethylation is generally accompanied by gene expression. A review of studies on DNA methylation in some physiopathologic conditions (such as development and cancer) and of recent therapeutic trials in beta thalassemia, allows to conclude that there is a correlation between DNA methylation pattern and gene expression, rather than a direct causal effect.

Properties of purified tyrosine aminotransferase from adult and senescent rat liver.

Induced tyrosine aminotransferase from adult and old rat liver was purified and its properties were studied. No differences could be detected for any physicochemical properties studied, i.e. specific activity, molecular weight, isoelectric point, thermostability, sensitivity to trypsin, Km for pyridoxal phosphate. Moreover, some age-related modifications previously described such as increased sensitivity to trypsin for induced old enzyme were no longer found. Tyrosine aminotransferase provides another argument against the 'error theory' of cellular aging.

Molecular studies of liver aldolase B in hereditary fructose intolerance using blotting and immunological techniques.

Hereditary fructose intolerance is due to a deficiency of liver aldolase (aldolase B). Little is known about its molecular mechanisms. We have tried to demonstrate the presence of the molecule and have explored the possibility of genetic heterogeneity. Liver samples from fifteen cases of hereditary fructose intolerance due to aldolase B deficiency were studied by various electrophoretic techniques. After electrophoresis on polyacrylamide gels, proteins were electrophoretically transferred on to nitrocellulose filters. They were treated with specific antialdolase B antibodies, and then with radioiodinated protein A, followed by autoradiography. Investigations included: (a) sodium dodecyl sulphate electrophoresis, in order to detect the presence of immunologically reactive molecules and to estimate the subunit size; (b) attempts to discover charge anomalies of the native molecule and of its subunits, by the use of: Isoelectric focusing of the native enzyme. Isoelectric focusing and non-equilibrium pH gradient electrophoresis (NEPHGE) after dissociation in urea. The major results were the following: (1) In all cases a cross-reacting material was found, with a molecular subunit size of 38000, indistinguishable from that of controls. (2) Evidence for molecular heterogeneity of the disease was provided by two types of data: amount of apparent immunologically reactive protein, which varied from less than 3% to 100% of that of controls; and charge data, aldolase B from seven patients showing an increased negative charge and from one patient a normal charge.

Cell types involved in the expression of foetal aldolases during rat azo-dye hepatocarcinogenesis.

Cellular and subcellular immunolocalization of aldose isozymes and alpha-foetoprotein (AFP) was performed in rat liver during the different stages of carcinogenesis induced by 3'-methyl-4-dimethylaminoazobenzene. During the early stages, double-labelling experiments showed that oval and transitional cells that expressed foetal aldolases did not contain adult aldolase B; this isozyme was only found in small and "normal' hepatocytes. AFP was present in transitional cells and in small hepatocytes. During hyperplastic nodule development, neither foetal aldolases nor AFP were located in hepatocytes. These foetal proteins were still observed in transitional cells. In hepatocellular carcinomas, both foetal proteins (aldolase isozymes and AFP) and adult aldolase B were present in malignant cells. Moreover, during the different stages foetal aldolases were also found in sinusoidal cells. These results indicate that, during azo-dye hepatocarcinogenesis, (a) several cell types synthesize foetal aldolases: oval and transitional cells, hepatoma cells and sinusoidal cells; (b) only hepatoma cells and not hepatocytes located in hyperplastic nodules can express both foetal and adult aldolases. This suggests that in primary, as in transplanted, hepatoma the resurgence of foetal isozymes is the consequence of a disturbance of control gene expression.

Isozyme differentiation of aldolase and pyruvate kinase in fetal, regenerating, preneoplastic, and malignant rat hepatocytes during culture.

Aldolase and pyruvate kinase isozymes were investigated in cultured hepatocytes from fetal, regenerating, and 2-acetyl-aminofluorene-fed rat liver as well as in some epithelial liver cell lines. Our results show that: (a) cell proliferation and prolonged expression of specific isozymes were found only in cultured hepatocytes from 17-day old fetuses; (b) the fetal type of pyruvate kinase expressed in regenerating and carcinogen-treated liver was temporarily lost only in cultured hepatocytes from regenerating liver; (c) the adult type of aldolase and pyruvate kinase was absent in one epithelial cell line derived from a carcinogen-treated liver and in the hepatoma tissue cell (HTC) line but was found in the Faza clone of the Reuber H35 cell line during the 50 first passages in vitro; and (d) the isozyme pattern of pyruvate kinase was always more strongly shifted than that of aldolase. The observations suggest that: (a) hepatocytes from carcinogen-treated liver exhibit the same lack of ability to proliferate in primary culture as normal adult hepatocytes; (b) adult hepatocytes can produce fetal isozymes without prior cell division; (c) pyruvate kinase is a stronger marker of dedifferentiation (retrodifferentiation) than aldolase; and (d) regulatory processes of isozyme expression are different during ontogenesis, regeneration, and hepatocarcinogenesis.

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.

Immunolocalization of fetal aldolase isoenzymes in rat regenerating liver after carbon tetrachloride intoxication.

Light and electron microscopic immunolocalization of adult and fetal aldolase isoenzymes has been studied in rat liver 72 h after CCL4 intoxication. As in rat regenerating liver after partial hepatectomy, fetal aldolases A and C were located in sinusoidal cells (Kupffer and endothelial cells) whereas adult aldolase B was present in hepatocytes only. Our results are different from those obtained with fetal and cancerous livers; they suggest that control mechanisms of gene regulation different in liver regeneration and in cancer.

Tyrosine aminotransferase in senescent rat liver.

We have studied tyrosine aminotransferase in the liver of adult and old rats. Thermostability and trypsin action were not modified, and no charge differences have been found by isoelectric focusing between 'adult' and 'old' enzymes. Inducibility by glucocorticoids was increased in vivo in these 27- to 31-month-old rats, but not in vitro, in cultured hepatocytes. Moreover, we have shown the absence of 'cross-reacting material' for tyrosine aminotransferase in senescent rat livers. The rapid turnover of this enzyme may explain the apparent absence of alterations during aging.

Isoelectrofocusing of erythrocyte galactose 1 phospho uridyl transferase in a family with both galactosemia and Duarte variants.

A family with the presence of the genes for both galactosemia and the Duarte variant is described. Galactose 1 phospho uridyl transferase has been studied not only by electrophoresis on starch gel, but also by isoelectro-focusing on thin-layer acrylamide. Normal and variant transferases were resolved into three bands, the isoelectric point of which was between 5.40 and 5.10 for the normal subjects, and between 5.25 and 4.95 for subjects with the Duarte variant.

Prenatal diagnosis of galactosemia.

We have monitored 3 pregnancies at risk for galactosemia by deficiency in Galactose-1-Phospho uridyl transferase. Galactosemia was diagnosed in the 1st case; heterozygoty in the 2nd, and a "double heterozygoty" in the 3rd. The latter is the first example of such a diagnosis. Post natal confirmation was obtained in the three cases. Arguments are given for the usefulness of this prenatal diagnosis.

Isozymes and differentiation.

We have tried to define "isozymes" and "differentiation" because these words are often used in a too vague sense. We have noted that the physiological role of isozymes is far from being clearly understood, even for the most studied enzyme with multiple molecular forms, lactic dehydrogenase. But we have pointed out that some isozymes are specific for some adult tissues, especially liver and muscle. They constitute consequently true "markers" of differentiation. Some mechanisms of this differentiation have been made clearer by the experiments of cell hybridization. The role of isozymes in differentiation is also illustrated by the selective disappearance of isozymic markers in some pathologycal conditions, for example : cancer and muscular diseases.