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P R Jennings

Publications and source records attributed to P R Jennings.

At least 19 recordsLinked to original sources
PubMed1997

A vertical (pseudodominant) pattern of inheritance in the autosomal recessive disease primary hyperoxaluria type 1: lack of relationship between genotype, enzymic phenotype, and disease severity.

Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease caused by a deficiency of alanine:glyoxylate aminotransferase (encoded by the AGXT gene). Primary hyperoxaluria type 1 is characterized by the elevated urinary excretion of oxalate and glycolate, and the deposition of insoluble calcium oxalate in the renal parenchyma and urinary tract. In the present study, we investigated an unusual family containing four affected individuals in two different generations. Based on our genetic, enzymic, metabolic, and clinical analyses, we have come to the following conclusions. First, although the pattern of inheritance of PH1 is usually horizontal (ie, all patients in the same generation), as expected for an autosomal recessive disease, it can sometimes show a vertical (pseudodominant) pattern of inheritance (ie, patients in more than one generation) due to the segregation within a family of three, rather than two, mutant AGXT alleles. Second, affected members of such a family can manifest very different clinical phenotypes both within and between generations. Although the clinical differences between generations might be at least partly due to differences in AGXT genotype, differences can equally occur within the same generation in individuals who possess the same AGXT genotype. Finally, individuals with PH1 at the level of the AGXT genotype might remain asymptomatic and undiagnosed for many years. The consequences of these findings for the clinical management and genetic counseling of families with PH1 are profound and wide-ranging.

Adolescent↗
PubMed1995

Mammalian alanine/glyoxylate aminotransferase 1 is imported into peroxisomes via the PTS1 translocation pathway. Increased degeneracy and context specificity of the mammalian PTS1 motif and implications for the peroxisome-to-mitochondrion mistargeting of AGT in primary hyperoxaluria type 1.

Alanine/glyoxylate aminotransferase 1 (AGT) is peroxisomal in most normal humans, but in some patients with the hereditary disease primary hyperoxaluria type 1 (PH1), AGT is mislocalized to the mitochondria. In an attempt to identify the sequences in AGT that mediate its targeting to peroxisomes, and to determine the mechanism by which AGT is mistargeted in PH1, we have studied the intracellular compartmentalization of various normal and mutant AGT polypeptides in normal human fibroblasts and cell lines with selective deficiencies of peroxisomal protein import, using immunofluorescence microscopy after intranuclear microinjection of AGT expression plasmids. The results show that AGT is imported into peroxisomes via the peroxisomal targeting sequence type 1 (PTS1) translocation pathway. Although the COOH-terminal KKL of human AGT was shown to be necessary for its peroxisomal import, this tripeptide was unable to direct the peroxisomal import of the bona fide peroxisomal protein firefly luciferase or the reporter protein bacterial chloramphenicol acetyltransferase. An ill-defined region immediately upstream of the COOH-terminal KKL was also found to be necessary for the peroxisomal import of AGT, but again this region was found to be insufficient to direct the peroxisomal import of chloramphenicol acetyltransferase. Substitution of the COOH-terminal KKL of human AGT by the COOH-terminal tripeptides found in the AGTs of other mammalian species (SQL, NKL), the prototypical PTS1 (SKL), or the glycosomal PTS1 (SSL) also allowed peroxisomal targeting, showing that the allowable PTS1 motif in AGT is considerably more degenerate than, or at least very different from, that acceptable in luciferase. AGT possessing the two amino acid substitutions responsible for its mistargeting in PH1 (i.e., Pro11-->Leu and Gly170-->Arg) was targeted mainly to the mitochondria. However, AGTs possessing each amino acid substitution on its own were targeted normally to the peroxisomes. This suggests that Gly170-->Arg-mediated increased functional efficiency of the otherwise weak mitochondrial targeting sequence (generated by the Pro11-->Leu polymorphism) is not due to interference with the peroxisomal targeting or import of AGT.

Alanine Transaminase↗
PubMed1994

Primary hyperoxaluria type 1: genotypic and phenotypic heterogeneity.

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disease caused by a deficiency of the liver-specific peroxisomal enzyme alanine: glyoxylate aminotransferase (AGT). The disease is notable for its extensive heterogeneity at the clinical, biochemical, enzymic and molecular genetic levels. A study of 116 PH1 patients over the past 8 years has revealed four main enzymic phenotypes: (1) absence of both AGT catalytic activity and immunoreactive AGT protein (approximately 40% of patients); (2) absence of AGT catalytic activity but presence of immunoreactive protein (approximately 16% of patients); (3) presence of both AGT catalytic activity and immunoreactive protein (approximately 41% of patients), in most of which cases the AGT is mistargeted to the mitochondria instead of the peroxisomes; and (4) a variation of the mistargeting phenotype in which AGT is equally distributed between peroxisomes and mitochondria, but in which that in the peroxisomes is aggregated into matrical core-like structures (approximately 3% of patients). Various point mutations, all occurring at conserved positions in the coding regions of the AGT gene, have been identified in these patients. The five mutations discussed in the present study, which have been found in individuals manifesting all of the four major enzymic phenotypes, account for the expressed alleles in about half of all Caucasian PH1 patients. The most common mutation found so far leads to a Gly170-->Arg amino acid substitution. This mutation, in combination with a normally occurring Pro11-->Leu polymorphism, appears to be responsible for the unprecedented peroxisome-to-mitochondrion mistargeting phenotype.

Amino Acid Sequence↗
PubMed1994

Cytosolic compartmentalization of hepatic alanine:glyoxylate aminotransferase in patients with aberrant peroxisomal biogenesis and its effect on oxalate metabolism.

Two patients with atypical manifestations of aberrant peroxisomal biogenesis are described. Contrary to previous studies, which had shown that Zellweger syndrome patients usually have normal levels of urinary oxalate excretion, the patients in the present study had evidence of abnormal oxalate metabolism in the form of hyperoxaluria and, in one of the patients, calcium oxalate urolithiasis. Activity of the liver-specific peroxisomal enzyme alanine:-glyoxylate aminotransferase (AGT), which is a major determinant of the level of endogenous oxalate synthesis in humans, was normal in one patient and markedly supranormal in the other. Using the technique of post-embedding protein A-colloidal gold immunoelectron microscopy, AGT was found to be mainly cytosolic in the livers of both patients, with significant amounts also localized in the nuclei. In a small minority of the hepatocytes of one patient, who was homozygous for the more common (major) AGT allele, large numbers of unidentified fibrillar arrays were found in the cytosol, which labelled heavily for immunoreactive AGT. The background cytosolic AGT labelling was markedly reduced in such cells when compared to the majority of cells that did not contain fibrils. In the other patient, who was heterozygous for the major and minor AGT alleles, there appeared to be low levels of mitochondrial AGT labelling. In the light of these data, the possible metabolic function of cytosolic AGT in the livers of panperoxisomal disease patients is discussed.

Alanine Transaminase↗
PubMed1994

Evolution of alanine:glyoxylate aminotransferase 1 peroxisomal and mitochondrial targeting. A survey of its subcellular distribution in the livers of various representatives of the classes Mammalia, Aves and Amphibia.

As part of a wider study on the molecular evolution of alanine:glyoxylate aminotransferase 1 (AGT1) intracellular compartmentalization, we have determined the subcellular distribution of immunoreactive AGT1, using postembedding protein A-gold immunoelectron microscopy, in the livers of various members of the classes Mammalia, Aves, and Amphibia. As far as organellar distribution is concerned, three categories could be distinguished. In members of the first category (type I), all, or nearly all, of the immunoreactive AGT1 was concentrated within the peroxisomes. In the second category (type II), AGT1 was found more evenly distributed in both peroxisomes and mitochondria. In the third category (type III), AGT1 was localized mainly within the mitochondria with much lower, but widely variable, amounts in the peroxisomes. Type I animals include the human, two great apes (gorilla, orangutan), two Old World monkeys (anubis baboon, Japanese macaque), a New World monkey (white-faced Saki monkey), a lago, morph (European rabbit), a bat (Seba's short-tailed fruit bat), two caviomorph rodents (guinea pig, orange-rumped agouti), and two Australian marsupials (koala, Bennett's wallaby). Type II animals include two New World monkeys (common marmoset, cotton-top tamarin), three prosimians (brown lemur, fat-tailed dwarf lemur, pygmy slow loris), five rodents (a hybrid crested porcupine, Colombian ground squirrel, laboratory rat, laboratory mouse, golden hamster), an American marsupial (grey short-tailed opossum), and a bird (raven). Type III animals include the large tree shrew, three insectivores (common Eurasian mole, European hedgehog, house shrew), four carnivores (domestic cat, ocelot, domestic dog, polecat ferret), and an amphibian (common frog). In addition to these categories, some animals (e.g. guinea pig, common frog) possessed significant amounts of cytosolic AGT1. Whereas the subcellular distribution of AGT1 in some orders (e.g. Insectivora and Carnivora) did not appear to vary markedly between the different members, in other orders (e.g. Primates, Rodentia and Marsupialia) it fluctuated widely between the different species. Phylogenetic analysis indicates that the subcellular distribution of AGT1 has changed radically on numerous occasions during the evolution of mammals. The new observations presented in this paper are compatible with our previous demonstration of a relationship between AGT1 subcellular distribution and either present or putative ancestral dietary habit, and our previous suggestion that the molecular evolution of the AGT gene has been markedly influenced by dietary selection pressure.

Alanine Transaminase↗
PubMed1993

Enzymological and mutational analysis of a complex primary hyperoxaluria type 1 phenotype involving alanine:glyoxylate aminotransferase peroxisome-to-mitochondrion mistargeting and intraperoxisomal aggregation.

Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease caused by a deficiency of the liver-specific peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT). Three unrelated PH1 patients, who possess a novel complex phenotype, are described. At the enzymological level, this phenotype is characterized by a complete, or nearly complete, absence of AGT catalytic activity and reduced AGT immunoreactivity. Unlike normal individuals in whom the AGT is confined to the peroxisomal matrix, the immunoreactive AGT in these three patients was distributed approximately equally between the peroxisomes and mitochondria. The peroxisomal AGT appeared to be aggregated into amorphous core-like structures in which no other peroxisomal enzymes could be identified. Mutational analysis of the AGT gene showed that two of the three patients were compound heterozygotes for two previously unrecognized point mutations which caused Gly41-->Arg and Phe152-->Iso amino acid substitutions. The third patient was shown to be a compound heterozygote for the Gly41-->Arg mutation and a previously recognized Gly170-->Arg mutation. All three patients were homozygous for the Pro11-->Leu polymorphism that had been found previously with a high allelic frequency in normal populations. It is suggested that the Phe152-->Iso and Gly170-->Arg substitutions, which are only eighteen residues apart and located in the same highly conserved internal region of 58 amino acids, might be involved in the inhibition of peroxisomal targeting and/or import of AGT and, in combination with the Pro11-->Leu polymorphism, be responsible for its aberrant mitochondrial compartmentalization. On the other hand, the Gly41-->Arg substitution, either in combination with the Pro11-->Leu polymorphism or by itself, is predicted to be responsible for the intraperoxisomal aggregation of the AGT protein.

Adult↗
PubMed1991

Enzymological characterization of a putative canine analogue of primary hyperoxaluria type 1.

This paper concerns an enzymological investigation into a putative canine analogue of the human autosomal recessive disease primary hyperoxaluria type 1 (alanine:glyoxylate/serine:pyruvate aminotransferase deficiency). The liver and kidney activities of alanine:glyoxylate aminotransferase and serine:pyruvate aminotransferase in two Tibetan Spaniel pups with familial oxalate nephropathy were markedly reduced when compared with a variety of controls. There were no obvious deficiencies in a number of other enzymes including D-glycerate dehydrogenase/glyoxylate reductase which have been shown previously to be deficient in primary hyperoxaluria type 2. Immunoblotting of liver and kidney homogenates from oxalotic dogs also demonstrated a severe deficiency of immunoreactive alanine:glyoxylate aminotransferase. The developmental expression of alanine:glyoxylate/serine:pyruvate aminotransferase was studied in the livers and kidneys of control dogs. In the liver, enzyme activity and immunoreactive protein were virtually undetectable at 1 day old, but then increased to reach a plateau between 4 and 12 weeks. During this period the activity was similar to that found in normal human liver. The enzyme activities and the levels of immunoreactive protein in the kidneys were more erratic, but they appeared to increase up to 8 weeks and then decrease, so that by 36 weeks the levels were similar to those found at 1 day. The data presented in this paper suggest that these oxalotic dogs have a genetic condition that is analogous, at least enzymologically, to the human disease primary hyperoxaluria type 1.

Alanine Transaminase↗
PubMed1990

Subcellular distribution of hepatic alanine:glyoxylate aminotransferase in various mammalian species.

The subcellular distribution of alanine:glyoxylate aminotransferase 1 (AGT1) enzyme activity and immunoreactive protein has been determined in the livers of a variety of mammalian species (marmoset, baboon, cat, rabbit, pig, sheep) using the techniques of post-embedding protein A-gold immunoelectron microscopy and isopycnic density gradient centrifugation. In baboon and rabbit livers, AGT1 was exclusively peroxisomal. Morphometric analysis of the distribution of immunoreactive AGT1 protein in cat liver showed that 91-92% was located in the mitochondria with 8-9% in the peroxisomes. In marmoset liver, 59% of AGT1 was found in the mitochondrial matrix and 41% in the peroxisomal matrix. The results from pig and sheep were ambiguous, because of the low levels of expression of AGT1. The implications of these data in terms of the metabolic roles of AGT1 (gluconeogenesis and glyoxylate detoxification) and in terms of the evolutionary acquisition and loss of functional mitochondrial and peroxisomal targeting sequences are discussed.

Alanine Transaminase↗
PubMed1989

Fetal liver alanine: glyoxylate aminotransferase and the prenatal diagnosis of primary hyperoxaluria type 1.

Primary hyperoxaluria type 1 (PH1) is caused by a deficiency of the hepatic peroxisomal enzyme alanine: glyoxylate aminotransferase (AGT, EC 2.6.1.44) (Danpure and Jennings, FEBS Lett., 201, 20-24, 1986). The activity of AGT has been measured in fetal livers of gestational age 14-21 weeks. Activity increases up to 17 weeks and then levels off between 17 and 21 weeks. At this time, the mean AGT activity is about 30 per cent of the mean normal postnatal level. As in adult liver, the AGT enzyme activity and the AGT immunoreactive protein are peroxisomal. Prenatal diagnosis has been performed by measuring AGT enzyme activity and immunoreactive AGT protein on liver biopsies from two fetuses at risk for primary hyperoxaluria type 1. One was unaffected and one was affected.

Alanine Transaminase↗
PubMed1989

Enzymological characterization of a feline analogue of primary hyperoxaluria type 2: a model for the human disease.

This paper concerns an enzymological investigation into a putative feline analogue of the human autosomal recessive disease primary hyperoxaluria type 2. The hepatic activities of D-glycerate dehydrogenase, using both D-glycerate and hydroxypyruvate as substrates, and glyoxylate reductase, which are the deficient enzyme activities in human primary hyperoxaluria type 2, were markedly depleted in four affected cats (0-6% of controls). The activities of a number of other enzymes, lactate dehydrogenase, glutamate dehydrogenase, D-amino acid oxidase, aspartate:2-oxoglutarate amino-transferase, glutamate:glyoxylate aminotransferase and alanine:glyoxylate aminotransferase (the deficient enzyme in primary hyperoxaluria type 1) were unaltered. The intracellular distribution of D-glycerate dehydrogenase and glyoxylate reductase in cat liver was shown to be cytosolic, as they are in human liver. The activities of D-glycerate dehydrogenase and glyoxylate reductase were determined in unaffected related cats and putative heterozygotes were identified. The correlation between D-glycerate dehydrogenase and glyoxylate reductase activities in the related cats and their combined deficiency in the affected cats confirmed previous suggestions that they are identical gene products.

Alcohol Oxidoreductases↗
PubMed1989

An enzyme trafficking defect in two patients with primary hyperoxaluria type 1: peroxisomal alanine/glyoxylate aminotransferase rerouted to mitochondria.

Most patients with the autosomal recessive disease primary hyperoxaluria type 1 (PH1) have a complete deficiency of alanine/glyoxylate aminotransferase (AGT) enzyme activity and immunoreactive protein. However a few possess significant residual activity and protein. In normal human liver, AGT is entirely peroxisomal, whereas it is entirely mitochondrial in carnivores, and both peroxisomal and mitochondrial in rodents. Using the techniques of isopycnic sucrose and Percoll density gradient centrifugation and quantitative protein A-gold immunoelectron microscopy, we have found that in two PH1 patients, possessing 9 and 27% residual AGT activity, both the enzyme activity and immunoreactive protein were largely mitochondrial and not peroxisomal. In addition, these individuals were more severely affected than expected from the levels of their residual AGT activity. In these patients, the PH1 appears to be due, at least in part, to a unique trafficking defect, in which peroxisomal AGT is diverted to the mitochondria. To our knowledge, this is the first example of a genetic disease caused by such interorganellar rerouting.

Adolescent↗