Isozymes and genetic control of NADP-malate dehydrogenase in mice

Location of theSas-1 locus on mouse chromosome 1

Using three sets of recombinant inbred strains (BXD, BXH, and BXJ), we found the locus controlling an antigenic substance (Sas}-1) in murine serum to be closely linked to the Chromosome-1 marker,Dip-1. This linkage was confirmed by an analysis of backcross linkage. The BXD and backcross data suggest that the gene order isId-1-Dip-1-Sas-1-Mls. Data from the three sets of RI strains and the 32 backcross mice lead to the estimate that the recombination frequency betweenDip-1 andSas-1 is 0.030 ±0.015.

Equine marker genes: Polymorphism for soluble erythrocyte malic enzyme

Polymorphism of equine erythrocyte malic enzyme is detactable on starch gel electrophoresis. The frequency of ME1S was 0.06 in 667 Standardbred and 0.09 in 85 Thoroughbred horses. No genetically determined electrophoretic variation in soluble malate dehydrogenase was detected.

Independent segregation of two functional markers expressed on the same B-cell subset in the mouse: the Mls determinants and LPS receptors

Mice of the C3H/Tif strain display a mixed leukocyte reaction (MLR) with all H-2k strains carrying any of the known alleles of the Mls locus. In particular, C3H/Tif is incompatible with the related substrain C3H/HeJ, from which it also differs at the locus responsible for the recognition of lipopolysaccharides (LPS) as B-cell mitogens, and at the Mod-1 locus. Our genetic analysis indicates that the MLR incompatibility between these strains is not H-2-linked and segregates as controlled by a single locus, most probably identical to Mls, for which the C3H/Tif strain expresses a previously unidentified allele, Mlse. Moreover, segregation data show that this locus assorts independently of LPS responsiveness and that neither marker is closely linked to the Mod-1 locus in linkage group II.

Differentiation in culture of cells from an avian holocrine secretory gland: preparation of isolated cells and conditions which induce accumulation of malic enzyme

Mammalian sebaceous glands contain cells which are constantly going through a process of cell division, differentiation, and destruction. Birds have an analogous holocrine secretory gland, the uropygial gland, which is an excellent model for mammalian sebaceous glands and for analysis of the regulation of differentiation. Isolated uropygial cells were purified in good yield, and with high viability, after enzymatic digestion of the duck uropygial gland. Almost exclusively progenitor (basal) cells are recovered after separation of isolated cells on a Percoll density gradient; mature uropygial cells are destroyed during preparation of isolated cells. In primary culture, uropygial gland cells grow to confluence and partially duplicate the in vivo differentiation pathway. Malic enzyme activity increases 30-fold during 4 wks in culture, but there is little, if any, accumulation of fatty acid synthase and only a modest deposition of fat droplets. Medium conditioned by chick embryo fibroblasts inhibits the accumulation of malic enzyme without affecting cell growth. The basement membrane components, collagen, laminin, and Matrigel, which stimulate differentiation in other cell systems, were without effect on uropygial gland cultures. Triiodothyronine, cyclic AMP, and dexamethasone together with isobutylmethylxanthine had no effect on cell growth or malic enzyme activity. Epidermal growth factor, which stimulates cell division, increased cell number with no increase in malic enzyme accumulation. Factors which would stimulate further differentiation are missing from our culture system, but may include components of the basal lamina and/or factors secreted by mesenchymal cells.

Purification and properties of cytosolic malic enzyme from human skeletal muscle

1. An NADP+-dependent malic enzyme was purified 7940-fold from the cytosolic fraction of human skeletal muscle with a final yield of 55.8% and a specific activity of 38.91 units/mg of protein. 2. The purification to homogeneity was achieved by ammonium sulfate fractionation, DEAE-Sepharose chromatography, affinity chromatography on NADP+-Agarose, gel filtration on Sephacryl S-300 and rechromatography on the affinity column. 3. Either Mn2+ or Mg2+ was required for activity: the pH optima with Mn2+ and Mg2+ were 8.1 and 7.5, respectively. The enzyme showed Michaelis-Menten kinetics. At pH 7.5 the apparent Km values with Mn2+ and Mg2+ for L-malate and NADP+ were 0.246 mM and 5.8 microM, and 0.304 mM and 5.8 microM, respectively. The Km values with Mn2+ for pyruvate, NADPH and bicarbonate were 8.6 mM, 6.1 microM and 22.2 mM, respectively. 4. The enzyme was also able to decarboxylate malate in the presence of NAD+. At pH 7.5 the reaction rate was approximately 10% of the rate in the presence of NADP+, with a Km value for NAD+ of 13.9 mM. 5. The following physical parameters were established: s0(20.w) = 10.48, Stokes' radius = 5.61 nm, pI = 5.72 Mr of the dissociated enzyme = 61,800. The estimates of the native apparent Mr yielded a value of 313,000 upon gel filtration, and 255,400 with f/fo = 1.33 by combining the chromatographic data with the sedimentation measurements. 6. The electron microscopy analysis of the uranyl acetate-stained enzyme revealed a tetrameric structure. 7. Investigations to detect sugar moieties indicated that the enzyme contains carbohydrate side chains, a property not previously reported for any other malic enzyme.

Evidence for two distinct mitochondrial malic enzymes in human skeletal muscle: purification and properties of the NAD(P)+-dependent enzyme

Human muscle mitochondria reduced either NADP+ or NAD+ in the presence of L-malate and Mn2+ or Mg2+. After polyacrylamide slab gel electrophoresis and agarose gel isoelectrofocusing, two bands were seen in mitochondrial extract, one strictly NADP+-dependent and the other reacting with either NAD+ or NADP+. The two mitochondrial malic enzymes were separated by DEAE-Sepharose chromatography. The NAD+/NADP+-dependent enzyme was purified 1600-fold with a final yield of 34% and a final specific activity of 32.9 units/mg of protein by employing affinity chromatography on Agarose-ATP. SDS electrophoresis revealed a single band having an apparent Mr = 64,000. Estimates of the native apparent molecular weight upon gel filtration yielded a value of 140,300. Kinetic characterization showed that succinate and ATP were activator and inhibitor, respectively. In the absence of succinate the Km values for malate, NAD+ and NADP+ were 3.7, 0.13 and 0.78 mM, respectively; in the presence of succinate the Km value for malate was 1.9 mM. ATP was found to be an inhibitor competitive with malate, with a Ki (ATP) of 0.2 mM. This is the first report to show that mammalian skeletal muscle mitochondria contains two distinct malic enzymes, one active with either NAD+ or NADP+ and the other active only with NADP+.

Changes of the NADP-linked malic enzyme in the developing rat skeletal muscle

The activities of NADP-linked malic enzyme, hexose monophosphate shunt dehydrogenases and NADP-linked isocitrate dehydrogenase were studied during development of skeletal muscle and compared with those in the liver. The variation patterns of malic enzyme activity in the liver and in the skeletal muscle were very similar, however the amplitude of the changes was different. The enzyme activity increased approx 16-fold in the liver and about 2-fold in skeletal muscle at the same stage of development. In skeletal muscle the increase of the malic enzyme activity was only slightly higher than of lactic dehydrogenase and citrate synthase. Studies on the intracellular distribution of malic enzyme in skeletal muscle showed that both mitochondrial and extramitochondrial enzymes increased between 20th and 37th day of life, the increase of the extramitochondrial enzyme being more pronounced. The hexose monophosphate shunt dehydrogenases activity showed an increase in the liver but no change was observed in the skeletal muscle at the weaning time. Changes in the activity of the liver and skeletal muscle isocitrate dehydrogenase were not significant between 10th and 80th day of life. The results suggest that the malic enzyme in the liver is playing a different physiological role than in the skeletal muscle.

Evidence for the role of malic enzyme in the rapid oxidation of malate by cod heart mitochondria

Mitochondria isolated from the heart of cod (Gadus morrhua callarias) oxidized malate as the only exogenous substrate very rapidly. Pyruvate only slightly increased malate oxidation by these mitochondria. This is in contrast with the mitochondria isolated from rat and rabbit heart which oxidized malate very slowly unless pyruvate was added. Arsenite and hydroxymalonate (an inhibitor of malic enzyme) inhibited the respiration rate of mitochondria isolated from cod heart, when malate was the only exogenous substrate. Inhibition caused by hydroxymalonate was reversed by the addition of pyruvate. In the presence of arsenite, malate was converted to pyruvate by cod heart mitochondria. Cod heart mitochondria incubated in the medium containing Triton X-100 catalyzed the reduction of NADP+ in the presence of L-malate and Mn2+ at relatively high rate (about 160 nmoles NADPH formed/min/mg mitochondrial protein). The oxidative decarboxylation of malate was also taking place when NADP+ was replaced by NAD+ (about 25 nmol NADH formed per min per mg mitochondrial protein). These results suggest that the mitochondria contain both NAD+- and NADP+-linked malic enzymes. These two activities were eluted from DEAE-Sephacel as two independent peaks. It is concluded that malic enzyme activity (presumably both NAD+- and NADP+-linked) is responsible for the rapid oxidation of malate (as the only external substrate) by cod heart mitochondria.

A new genetic variation of the malate dehydrogenase-like enzyme (MDL-1) in inbred rats and its possible linkage

A new polymorphism in the mitochondrial fraction of kidney homogenates was found by using discontinuous polyacrylamide gel electrophoresis. The polymorphism is tentatively designated MDL-1, since the enzyme was visualized with the staining solution for NADP-malate dehydrogenase (MOD) but differs from MOD. MDL-1 expresses three phenotypes: MDL-1A (fast), MDL-1AB (intermediate), and MDL-1B (slow). Progeny testing from genetic crosses indicates that its expression is determined by two codominant alleles, Mdl-1a and Mdl-1b, which segregate in a simple Mendelian fashion. Preliminary linkage data suggest that the locus for MDL-1 is probably linked to the nonagouti-agouti locus in rat linkage group IV.

Friedreich's disease 1982: etiologic hypotheses a personal analysis

The author reviews the arguments for and against the four etiologic hypotheses in Friedreich's disease that have been proposed since 1974: the "pyruvate hypothesis", the "lipid-membrane hypothesis", the "energy-defect hypothesis" and finally the "taurine hypothesis". While none of these hypotheses are mutually exclusive, the author shows that all of these mechanisms play some role in the pathophysiology of the symptoms, but that only the "taurine hypothesis" appears to be compatible with all the known facts and the biochemical abnormalities reported. The author proposed that the taurine retention defect (possibly due to a block in the high affinity-low capacity transport of taurine - The TH System) is a primary event in Friedreich's disease. Whether it is the primary genetic event still has to be determined.

Biochemical markers of three strains derived from Japanese wild mouse (Mus musculus molossinus)

Twenty-eight biochemical markers were examined in three strains (Mol-A, Mol-N and Mol-T) derived from the the Japanese wild mouse, Mus musculus molossinus, as well as five laboratory strains, Mus musculus musculus. The Mol strains showed specific alleles at as many as 12 loci. These findings emphasize that the Mol strains have significance in future genetic and developmental studies.

Deficiency of malic enzyme: a possible marker for malignancy in lymphoid cells

Soluble malic enzyme (MEs) has been examined in long-term human lymphoid cell lines cultured from 101 individuals. In 65 out of 66 lines derived from people without lymphoreticular malignancy the enzyme was very active. Lines established from 35 individuals with various forms of lymphoreticular malignancy were also examined, including in some cases more than 1 line derived from the same patient. In all cases where the cell line was thought to be derived from normal cells MEs was active, but in 27 out of 29 lines thought to be derived from malignant cells (from 25 patients) MEs was not detected. In the case of two patients with chronic lymphatic leukaemia 'normal' lines active for malic enzyme, and 'leukaemic' lines lacking malic enzyme, had been cultured from the same individual. Preliminary investigations of the lack of malic enzyme in somatic cell hybrids derived from lymphoma and leukaemia cell lines are compatible with an alteration at the level of the structural locus MEs on chromosome 6. However, the restoration of MEs activity in one line by fusion with mouse teratocarcinoma cells suggests that the alteration may be of a regulatory nature.

Purification and some properties of extramitochondrial malic enzyme from rat skeletal muscle

Extramitochondrial malic enzyme (L-malate:NADP+ oxidoreductase (oxaloacetate-decarboxylating), EC 1.1.1.40) has been isolated from postmitochondrial supernatant of rat skeletal muscle, by (NH4)2SO4 fractionation, chromatography on DEAE-cellulose, Sepharose 6B, ADP-Sepharose and Ultrogel AcA-34 to apparent homogeneity as judged from polyacrylamide gel electrophoresis. Specific activity of purified enzyme was 20 mumol . min-1 per mg protein, which corresponds to about 3000-fold purification. The molecular weight of the native enzyme was determined by gel filtration to be 264 000. Sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis showed one polypeptide band of molecular weight 63 000. Thus, it appears that the native protein is a tetramer composed of identical molecular weight subunits. The isoelectric point of the isolated enzyme was at pH 6.15. The enzyme was shown to carboxylate pyruvate in the presence of high concentrations of bicarbonate and pyruvate at about 80% of the rate of the forward reaction. The Km values, determined at pH 7.2 for malate and NADP, were 0.125 mM and 11 microM, respectively. The Km values for pyruvate, NADPH and bicarbonate were 4.0 mM, 6.6 microM and 24 mM, respectively. The optimum pH for carboxylation reaction was at pH 7.1. The optimum pH for decarboxylation reaction varied with the malate concentration. The purified malic enzyme catalyzed the decarboxylation of oxaloacetate at pH 4.5. In a system consisting of isolated rat skeletal muscle mitochondria, pyruvate, bicarbonate and NADPH, cytoplasmic malic enzyme is able to replace added malate in stimulating oxidation of acetyl-CoA formed by oxidative decarboxylation of pyruvate. It is suggested that extramitochondrial malic enzyme might be one of the enzymes involved in the anaplerotic supply of Krebs cycle intermediates in skeletal muscle.

Identification and biochemical analysis of mouse mutants deficient in cytoplasmic malic enzyme

During the biochemical screening of mutant enzymes in mice, individuals with an apparent nonfunctional allele at the locus (Mod-l) responsible for cytoplasmic malic enzyme were identified by starch gel electrophoresis and by enzyme activity measurements. A series of matings and genetic analyses were made, and mice homozygous for the nonfunctional or null allele (Mod-ln) were produced. The mutation appeared to occur spontaneously in the C57BL/6J strain. By double-immunodiffusion and enzyme immunoinactivation assays, the null mutants were shown to express no proteins that cross-react with the antiserum to cytoplasmic malic enzyme (CRM-negative). In liver homogenates of homozygous null mutants, lack of protein components that form complexes with IgG from the cytoplasmic malic enzyme specific antiserum was further demonstrated by passage of the original serum through a mutant liver homogenate--Sepharose column, where the postadsorbed serum retained its titer and specificity. The residual malic enzyme activity (< 10% of the normal) observed in various tissue homogenates of the homozygous null mutants was attributed to that of mitochondrial isozyme of malic enzyme. Assays of enzymes from tissues of different genotypes revealed no significant differences in activities of six other enzymes in the related metabolic pathways. However, in liver from mutant mice, a lower NADPH/NADP+ ratio was consistently observed in comparison to that from control mice. Both the mutant and the control mice of the same age were found to have comparable body weight and lipid content.

Isolation and regulatory properties of mitochondrial malic enzyme from rat skeletal muscle

Mitochondrial malic enzyme (L-malate:NADP+ oxidoreductase (oxalo-acetate-decarboxylating), EC 1.1.1.40) has been isolated from rat skeletal muscle by (NH4)2SO4 fractionation, chromatography on DEAE-cellulose and Ultrogel AcA 34. Specific activity of the purified enzyme was 25 micromol/min per mg of protein which corresponds to about 840-folf purification. The enzyme was shown to carboxylate pyruvate in the presence of high concentrations of KHCO3 and pyruvate at about 15% of the rate of the forward reaction. The Km values determined at pH 7.2 for malate, NADP and Mn2+ were 0.33 mM, 6.8 microM and 7.1 microM, respectively. The Km values for pyruvate, NADPH and KHCO3 were 8.3 mM, 19.6 microM, and 24.4 mM, respectively. Purified enzyme showed allosteric properties at low concentration of malate and this characteristic can be modified by succinate and fumarate which do not affect the maximum velocity of the reaction. The pH optimum for decarboxylation reaction was between 7.2 and 8.4. Possible metabolic role of mitochondrial malic enzyme in skeletal muscle is discussed.

Mitochondrial malic enzyme in mosaic skeletal muscle of mouse chimeras

The question was investigated whether mitochondria in the mammalian skeletal muscle fiber syncytium incorporate gene products encoded by one or many nuclei. Mouse chimeras were produced from strains which differ in their electrophoretic variants of the nuclear-coded mitochondrial protein, malic enzyme (MOD-2, E.C. 1.1.1.40, L-malate NADP+ oxidoreductase decarboxylating). The MOD-2 phenotypes of skeletal muscles of these chimeras were characterized in a starch gel electrophoretic system. The results indicate that individual mitochondria can contain products encoded by multiple nuclei and therefore that, for skeletal muscle mitochondria, the cell is not subdivided into nuclear territories. Possible mechanisms of gene product distribution in skeletal muscle fibers are discussed.

Segregation of rat chromosomes in somatic cell hybrids between rat cells and HT 1080 human fibrosarcoma cells

We produced somatic cell hybrids between HT 1080-6TG human fibrosarcoma cells and either rat white blood cells (WBC) or cells directly derived from rat spleen. Karyologic and isozyme analyses of hybrid cells indicated that they preferentially lose rat chromosomes. Hypoxanthine-aminopterine thymidine-selected hybrid clones expressing rat hypoxanthine phosphoribosyltransferase (HPRT), glucose-6-phosphate dehydrogenase (G6PD), and phosphoglycerate kinase (PGK) and containing the rat X chromosome were counterselected in a medium containing 30 micrograms/ml of 6-thioguanine. Concordant loss of the rat X chromosome and of the expression of rat HPRT and G6PD was observed in the hybrid clones.

Evidence for the presence of two sympatric species of mice (genus Mus L.) in southern France based on biochemical genetics

Populations of mice established outdoors as well as indoors have been investigated at 24 loci using starch gel electrophoresis. Two reproductively isolated groups are recognized, one of which is referable to a house mouse subspecies, Mus musculus brevirostris, and the other to a different species. Mus spretus, contrary to the view of Schwarz and Schwarz that only one species of Mus is present in the Mediterranean Basin. The genetic distance between these two groups is larger than between any pair of investigated subspecies of M. musculus. M. m. brevirostris is biochemically almost indistinguishable from M. m. domesticus. On the other hand, M. spretus exhibits several allelic variants unknown or at most very infrequent in M. musculus, as for instance at the lactate dehydrogenase B-chain locus.

Genetic variation in antibody response and natural killer cell activity against a Moloney virus-induced lymphoma (YAC)

Antibody formation against the Moloney virus-determined surface antigen (MCSA) was found to be under genetic control. In the (A X C57BL)F1 cross one dominant gene played a major role, resulting in bimodal distribution of the antibody response. This gene showed no linkage to H-2, IgG heavy chain immunoglobulin allotype, the coat color markers B and C, and five different isozyme markers representing chromosome numbers 1, 4, 7, 8 and 9. Antibody response to MCSA was not correlated with antibody titers against the virion proteins, confirming that MCSA was an independent entity. There was no relationship between the segregation of natural killer cell activity and antibody response in a [(A X C57BL) X A] backcross population.

Human mitochondrial malic enzyme variants: properties of the different polymorphic forms

1. The human mitochondrial malic enzyme polymorphism was found to exist in the Scottish population with similar allele frequencies to those reported previously for Caucasian populations. 2. The mitochondrial malic enzyme variants MEM1, MEM2-1 and MEM2 which form the polymorphism have been separated from the cytoplasmic malic enzyme and partially purified by DEAE Sephadex chromatography. 3. The properties of the three mitochondrial malic enzyme variants were examined. No differences were found between the variants in Km for NADP, Km for pyruvate, Mn2+ and Mg2+ activation, Ki for dicumarol, heat stability, pH or ionic strength optimum.

Sexual and parasexual approaches to the genetic analysis of the laboratory mouse, Mus musculus

The mouse genetic map has been characterized largely through breeding studies based on the principles of Mendelian genetics. More recently, specific genetic information has been obtained from somatic cell studies using the techniques of in situ hybridization and somatic cell hybridization. The genetic analysis possible through these sexual and parasexual approaches is described, and specific linkage information from recent somatic cell studies is reviewed.

Mitochondrial malate dehydrogenase (Mor-1) in the mouse: linkage to chromosome 5 markers

Malate dehydrogenase is present in most mammalian tissues in both supernatant and mitochondrial forms. Although genetic variation for the supernatant form has not been observed in the mouse, electrophoretic variants caused by alleles at the mitochondrial locus (Mor-1) have been previously described. We have located this locus 11.0 +/- 2.9 cM from the beta-glucuronidase structural gene, Gus, on chromosome 5. The gene order is Hm-Pgm-1-rd-bf-Gus-Mor-1. Thus Mor-1 is presently the most distal marker on chromosome 5. Three different nuclear loci for mitochondrial enzymes (Mod-2, Got-2, and Mor-1) have now been mapped in the mouse, all on different chromosomes.

Sub-unit structure of soluble and mitochondrial malic enzyme: demonstration of human mitochondrial enzyme in human-mouse hybrids

1. Malic enzyme has been examined by starch-gel electrophoresis in human cultured fibroblasts and in 60 brain samples. The polymorphism of MEM has been confirmed and the electrophoretic pattern suggests that this enzyme, like MES, is a tetramer. 2. The appearance of the soluble and mitochondrial malic enzymes in mouse and Chinese hamster is described, and the identity of the enzymes in man, mouse and hamster has been established from a study of interspecific somatic cell hybrids. In man and in hamster MES migrates anodal to MEM, whereas in the mouse MES is relatively less anodal than MEM. 3. Segregation of human enzymes in human--mouse and human--hamster somatic cell hybrids confirms the synteny of MES and PGM3. Data from human--mouse hybrids suggest that MEM is probably not syntenic with MES is probably not syntenic with MES in man, nor is it syntenic with GPI.

Enzyme synthesis in the regulation of hepatic "malic" enzyme activity

A homogeneous preparation of ;malic' enzyme (EC 1.1.1.40) from livers of thyroxine-treated rats was used to prepare in rabbits an antiserum to the enzyme that reacts monospecifically with the ;malic' enzyme in livers of rats in several physiological states. Changes in enzyme activity resulting from modification of the state of the animal are hence due to an altered amount of enzyme protein. The antiserum has been used to precipitate out ;malic' enzyme from heat-treated supernatant preparations of livers from both adult and neonatal rats, in a number of physiological conditions, that had been injected 30min earlier with l-[4,5-(3)H]leucine. The low incorporations of radioactivity into the immunoprecipitable enzyme have permitted the qualitative conclusion that changed enzyme activity in adult rats arises mainly from alterations in the rate of enzyme synthesis. The marked increase in ;malic' enzyme activity that occurs naturally or as a result of thyroxine treatment of the weanling rat is likewise due to a marked increase in the rate of enzyme synthesis possibly associated with a concurrent diminished rate of enzyme degradation.