Assignment of the gene for cytosolic alanine aminotransferase (AAT1) to human chromosome 8

cDNA cloning, expression, purification, distribution, and characterization of biologically active canine alanine aminotransferase-1

Alanine aminotransferase (ALT) is a pyridoxal enzyme found mainly in the liver and kidney, but also in small amounts in the heart, muscle, fat, and brain. Serum aminotransferase activities have been used broadly as surrogate markers for tissue injury and disease in human and veterinary clinical settings and in safety assessment of chemicals and pharmaceuticals. Because of its relative abundance in liver, increased serum ALT activity is generally considered indicative of liver damage. Two ALT isoenzymes, ALT1 and ALT2, are known and have been cloned and sequenced from human, rat, and mouse. In this study, we have cloned the complementary DNA encoding the canine orthologue of ALT1 (cALT1). The complete cDNA sequence comprised 1852 bases and contained a 1485-base open reading frame, which encodes a polypeptide of 494 amino acid residues. Canine ALT1 shares 87.7, 87.2, and 87.0% amino acid identity to its human, mouse, and rat orthologues, respectively. The cDNA was expressed in Escherichia coli, with a N-terminal His (6x) tag, and the recombinant enzyme was purified using immobilized metal-affinity chromatography. The final yield of the purified recombinant cALT1 was greater than 5mg/L culture. The alanine transaminase activity of purified cALT1 was 229.81U/mg protein, which is approximately 38-fold higher than that of total soluble recombinant E. coli cell lysate, confirming that the enzyme is a functional ALT. Evaluation of various canine tissues by RT-PCR revealed that the level of ALT1 expression is in the order of: heart>liver>fat approximately brain approximately gastrocnemius>kidney. The purified cALT1 will be helpful to develop isoenzyme-specific anti-bodies, which could further improve the diagnostic resolution of current ALT assays in drug safety studies.

Development of an electrochemical immunosensor for alanine aminotransferase

Alanine aminotransferase (ALT) has been regarded as one of the most sensitive indicators of hepatocellular damage. While ALT is widely used in the practice of medicine, few attempts have been made to develop biosensors applicable to the on-site diagnosis of liver diseases. In the hope of developing an immunosensor for measurement of ALT activity, we have generated monoclonal antibodies to human recombinant ALT and fabricated them for use in a sensor. The ALT immunosensor was composed of the followings: (1) anti-ALT antibody-immobilized outer membrane; (2) pyruvate oxidase-absorbed inner membrane; (3) a self assembled monolayer mediator-coated gold working electrode and an Ag/AgCl reference electrode. The chronoamperometric measurement of the immunosensor was performed with 40 microl of PBS containing substrates and ALT without a washing step in less than 5 min. The dynamic range of ALT immunosensor was presented as five orders of magnitude, ranging between 10 pg/ml and 1 microg/ml. The detection limit and the sensitivity were 10 pg/ml and 26.3 nA/(ng/ml), respectively. In the meantime, the enzyme sensor fabricated without anti-ALT antibody showed much poorer analytical values. The dynamic range, the detection limit, and the sensitivity were 10 ng/ml-100 microg/ml, 10 ng/ml and 11.4 nA/(ng/ml), respectively. The presented results indicated that the immunosensor system provided much better technical performance in all of the aspects evaluated than did the enzyme sensor without the immobilized-antibody.

A site-specific plectin mutation causes dominant epidermolysis bullosa simplex Ogna: two identical de novo mutations

Plectin is one of the largest and most versatile cytolinker proteins known. In basal keratinocytes it links the intermediate filament network to cell membrane-associated hemidesmosomes. Several mutations in its gene have been identified that lead to the recessive disease epidermolysis bullosa with muscular dystrophy. We report here a mutation that leads to a dominant form of the disease, epidermolysis bullosa simplex Ogna. We found that the epidermolysis bullosa simplex Ogna phenotype is due to a site-specific missense mutation within plectin's rod domain. Further, we show that epidermolysis bullosa simplex Ogna is not restricted to a single Norwegian kindred as previously believed. A German family with the phenotypic hallmarks of epidermolysis bullosa simplex Ogna was found to carry an identical de novo mutation. These two mutations arose about 200 y apart in time. Consistent with the absence of muscular symptoms in these patients, muscle biopsies from several epidermolysis bullosa simplex Ogna members of the Norwegian kindred showed normal staining patterns using antibodies to plectin. Skin changes in epidermolysis bullosa simplex Ogna patients are documented on the ultrastructural level.

Human glutamate pyruvate transaminase (GPT): localization to 8q24.3, cDNA and genomic sequences, and polymorphic sites

Two frequent protein variants of glutamate pyruvate transminase (GPT) (E.C.2.6.1.2) have been used as genetic markers in humans for more than two decades, although chromosomal mapping of the GPT locus in the 1980s produced conflicting results. To resolve this conflict and develop useful DNA markers for this gene, we isolated and characterized cDNA and genomic clones of GPT. We have definitively mapped human GPT to the terminus of 8q using several methods. First, two cosmids shown to contain the GPT sequence were derived from a chromosome 8-specific library. Second, by fluorescence in situ hybridization, we mapped the cosmid containing the human GPT gene to chromosome band 8q24.3. Third, we mapped the rat gpt cDNA to the syntenic region of rat chromosome 7. Finally, PCR primers specific to human GPT amplify sequences contained within a "half-YAC" from the long arm of chromosome 8, that is, a YAC containing the 8q telomere. The human GPT genomic sequence spans 2,7 kb and consists of 11 exons, ranging in size from 79 to 243 bp. The exonic sequence encodes a protein of 495 amino acids that is nearly identical to the previously reported protein sequence of human GPT-1. The two polymorphic GPT isozymes are the results of a nucleotide substitution in codon 14, coding for a histidine in GPT-1 and an asparagine in GPT-2, which causes a gain or loss of an NlaIII restriction site. In addition, a cosmid containing the GPT sequence also contains a previously unmapped, polymorphic microsatellite sequence, D8S421. The cloned GPT gene and associated polymorphisms will be useful for linkage and physical mapping of disease loci that map to the terminus of 8q, including atypical vitelliform macular dystrophy (VMD1) and epidermolysis bullosa simplex, type Ogna (EBS1). In addition, this will be a useful system for characterizing the telomeric region of 8q. Finally, determination of the molecular basis of the GPT isozyme variants will permit PCR-based detection of this world-wide polymorphism.

Plectin abnormality in epidermolysis bullosa simplex Ogna: non-responsiveness of basal keratinocytes to some anti-rat plectin antibodies

Epidermolysis bullosa (EB) is a heterogeneous group of genetic bullous skin diseases. The EB simplex group (EBS) is characterized by intraepidermal blistering. EBS-Ogna was first described as a separate entity based on clinical studies. Later genetic linkage of EBS-Ogna to the GPT locus for glutamate pyruvate transaminase (alanine transaminase) was detected and GPT was assigned to chromosome 8, then to the terminal long arm band 8q24. Plectin is an abundant and widespread cytoskeletal protein which has been proposed as a general crosslinking element of intermediate filaments. Human plectin has recently been cloned and in situ hybridized to chromosome 8q24. To examine whether plectin could be associated with EBS-Ogna we performed an immunohistochemical study with a panel of mAbs to rat plectin. Interestingly, 2 of these mAbs showed strong intracellular staining of the suprabasal and basal layer of the epidermis in all control samples, whereas no reactivity of the basal layer was found in the Ogna group. These results strongly suggest that plectin is involved in the pathogenesis of EBS-Ogna.

Gene dosage evidence for the regional assignment of GPT (glutamate-pyruvate transaminase; E.C. 2.6.1.2) locus to 8q24.2----8qter

The results of a study on the expression of GPT (glutamate-pyruvate transaminase; E.C. 2.6.1.2) in a child with a partial trisomy of chromosomes 8 and 14 are presented. A gene dosage effect supporting the regional assignment of the GPT locus to 8q24.2----8qter is demonstrated.

Human chromosome 8

The role of human chromosome 8 in genetic disease together with the current status of the genetic linkage map for this chromosome is reviewed. Both hereditary genetic disease attributed to mutant alleles at gene loci on chromosome 8 and neoplastic disease owing to somatic mutation, particularly chromosomal translocations, are discussed.

Developmental delay, short stature, and minor facial anomalies in a child with ring chromosome 16

We present a girl with ring chromosome 16. Clinical abnormalities included developmental delay, short stature, and minor facial anomalies. Analysis of the glutamate-pyruvate transaminase (GPT) phenotype suggests the possible exclusion of the GPT locus expressed in erythrocytes (GPT) from the very distal p13 region of chromosome 16.

Chromosome assignment, biochemical and immunological studies on a human aldehyde dehydrogenase, ALDH3

The biochemical properties of ALDH isozymes have been examined in human tissues and one set, designated ALDH3, has been studied in detail. These components occur at highest levels in lung and stomach, but were not expressed in fetal tissues, or in blood, hair roots and fibroblasts. The ALDH3 isozymes show optimal activity with benzaldehyde and can use either NAD or NADP as cofactor. Antiserum against a partially purified ALDH3, from stomach, selectively precipitates this isozyme from human tissues and selectively recognizes an homologous component in the rat. Human and rodent ALDH3 were not immunoprecipitated by anti-ALDH1 or anti-ALDH2 antisera. High levels of expression were found in human-rodent hybrids, constructed using rat hepatoma cells, and these hybrids were used to assign the human ALDH3 gene to chromosome 17.

Assignment of structural gene for asparagine synthetase to human chromosome 7

Somatic cell hybrids obtained from the fusion of human B lymphocytes and an asparagine synthetase-deficient Chinese hamster ovary cell line were isolated after growth in asparagine-free medium. The human and hamster forms of asparagine synthetase differ significantly in their rate of inactivation at 47.5 degrees C. The asparagine synthetase activity expressed in the hybrids was inactivated at 47.5 degrees C at the same rate as the human form of the enzyme. Karyotypic analysis and analysis for chromosome-specific enzyme markers showed that the structural gene for asparagine synthetase is located on chromosome 7 in humans. The heat-inactivation profile for asparagine synthetase in extracts of hybrids formed between human peripheral leukocytes and a hamster cell line expressing asparagine synthetase activity was intermediate between the two parental types when human chromosome 7 was present, but was identical to the hamster parent when chromosome 7 was absent.

Regulation of expression of liver-specific enzymes. III. Further analysis of a series of rat hepatoma X human somatic cell hybrids

1. The expression of twelve liver-specific enzymes was analysed in twenty-one independent rat hepatoma X human somatic cell hybrids, and in some cases up to forty-one subclones were also tested. 2. Seventeen hybrids continued to express most of the rat liver-specific enzymes and in some cases human isozymes of glutamate-pyruvate transaminase, alpha-glycerophosphate dehydrogenase, guanine deaminase, alcohol dehydrogenase and pyruvate kinase were clearly identified. 3. Analysis of the segregation of the human liver-specific enzymes in these hybrids led to the assignment of human GPT to chromosome 8 (previously reported, Kielty, Povey & Hopkinson, 1982) and suggests the assignment of human GPD1 to chromosome 12. 4. The expression of the various liver-specific enzymes in these hybrids appeared to be controlled by independent regulatory mechanisms. 5. Four unusual reverse segregant hybrids were also analysed, and in these no liver-specific enzyme activity was demonstrable.