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B Zhang

Publications and source records attributed to B Zhang.

At least 649 records · Page 36Linked to original sources
PubMed1991

Molecular defects in the E1 alpha subunit of the branched-chain alpha-ketoacid dehydrogenase complex that cause maple syrup urine disease.

Maple syrup urine disease (MSUD) results from an inborn metabolic error caused by a deficiency of the branched-chain alpha-ketoacid dehydrogenase complex (BCKDC). cDNA clones encoding the E1 alpha subunit of BCKDC from rat and human liver have been isolated and characterized. The chromosomal location of E1 alpha on chromosome 19q13.1-13.2 has been determined using complementary methods. The etiology of MSUD has been studied by determining the enzyme activity, protein mass and mRNA level of BCKDC in fibroblasts from a human family and Polled Hereford calves, both with classic MSUD. A TACTyr to AACAsn substitution at residue 394 of the E1 alpha subunit was identified in the human patient by using enzymatic amplification of mRNA followed by DNA sequencing. Amplification of both mRNA and genomic DNA, in combination with allele-specific oligonucleotide hybridization, demonstrated that the patient was a compound heterozygote, inheriting an allele with a structural mutation from the father, and an allele from the mother containing a presumably cis-acting defect in regulation that abolished the expression of one of the E1 alpha alleles. The results revealed for the first time that a case of MSUD was caused by structural and regulatory mutations involving the E1 alpha subunit. Recent studies by others have demonstrated that the same structural mutation as is found in this patient is responsible for the high incidence of MSUD in the Philadelphia Mennonite population.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1990

Analysis by base exchange of thyrotropin-releasing hormone responsive and unresponsive inositol lipid pools in rat pituitary tumor cells.

We have shown that there is an inositol (Ins) lipid pool in cloned rat pituitary tumor (GH3) cells that is hydrolyzed in response to thyrotropin-releasing hormone (TRH) and an unresponsive pool. Because others have suggested that incorporation of [3H]Ins by base exchange may not occur uniformly into Ins lipids in other cell types, we established conditions using permeabilized cells under which labeling occurs by Ins-phosphatidylinositol (PI) exchange in the absence of de novo PI synthesis to further characterize these pools in GH3 cells. In permeabilized cells incubated in buffer containing 10 mM Mg2+ and 0.1 mM CMP, [3H]Ins incorporation into lipids occurred by base exchange only. This was so because: 1) [3H]Ins incorporation into lipids displayed properties similar to that for release of 3H-labeled Ins by unlabeled Ins from PI in cells prelabeled in situ prior to permeabilization; and 2) there was no change in PI mass under these conditions. In permeabilized cells incubated in buffer with 0.1 mM [3H]Ins for 60 min, incorporation was 0.61 +/- 0.05 nmol of [3H]Ins/10(6) permeabilized cells, which amounted to 35% of PI, while the level of PI, measured as nonradioactive phosphorus, was 94 +/- 8.0% of control. Permeabilized GH3 cells were responsive to TRH. In cells prelabeled in situ and then permeabilized, TRH stimulated an increase in 3H-labeled Ins phosphates (IPs) in 20 min which was 10% of 3H radioactivity initially present in lipids. This increase in 3H-labeled IPs was 6.3 times the 3H radioactivity present in phosphatidylinositol 4,5-bisphosphate prior to stimulation. When prelabeled cells were exchanged with unlabeled Ins after permeabilization there was only a 10-16% decrease in 3H-labeled IP accumulation stimulated by TRH even though 3H-labeled lipids decreased to 52% of control. TRH did not affect labeling by [3H]Ins-PI exchange. In cells labeled by base exchange after permeabilization TRH stimulated a very small increase in 3H-labeled IPs of only 0.21 +/- 0.02% of 3H-labeled lipids in 20 min or only 7% of the 3H radioactivity in phosphatidylinositol 4,5-bisphosphate. These data show that in permeabilized GH3 cells base exchange can occur in the absence of de novo PI synthesis and that lipids that are preferentially labeled by base exchange comprise a pool that is less responsive to TRH than total Ins lipids.

Animals↗
PubMed1990

Premature translation termination of the pre-E1 alpha subunit of the branched chain alpha-ketoacid dehydrogenase as a cause of maple syrup urine disease in Polled Hereford calves.

Maple syrup urine disease in man and cattle is an inborn metabolic error caused by the deficiency of the branched chain alpha-ketoacid dehydrogenase. We have studied the molecular basis of the disease in Polled Hereford calves. The E1 component of branched chain alpha-ketoacid dehydrogenase was virtually undetectable by Western blot analysis of fibroblasts from an affected calf. Northern blot analysis failed to detect the E1 alpha mRNA species in the fibroblasts. Nevertheless, it was readily demonstrated by reverse transcription of RNA followed by polymerase chain reaction that the mRNA for the E1 alpha subunit was present in the cells, albeit at very low concentrations. Sequencing of the polymerase chain reaction-generated cDNA for the entire coding region of the E1 alpha subunit revealed a single base substitution at codon -6 (CAG to TAG). This mutation introduces a stop codon in the leader peptide of the E1 alpha subunit, resulting in the premature termination of translation. The mutation was verified by hybridization of the amplified cDNA fragments from two affected calves with allele-specific oligonucleotides. This finding explains the pathogenesis of maple syrup urine disease in this breed of cattle, which provides the only known animal model for the human disease. In addition, the results provide evidence for the effect of premature translation termination on reducing the steady-state mRNA level and the dependence of E1 beta protein stability on the co-expression of the E1 alpha.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1990

Regulation of the branched-chain alpha-ketoacid dehydrogenase and elucidation of a molecular basis for maple syrup urine disease.

The hepatic branched-chain alpha-ketoacid dehydrogenase complex plays an important role in regulating branched-chain amino acid levels. These compounds are essential for protein synthesis but toxic if present in excess. When dietary protein is deficient, the hepatic enzyme is converted to the inactive, phosphorylated state to conserve branched-chain amino acids for protein synthesis. When dietary protein is excessive, the enzyme is in the active, dephosphorylated state to commit the excess branched-chain amino acids to degradation. Inhibition of protein synthesis by cycloheximide, even when the animal is starving for dietary protein, results in activation of the hepatic branched-chain alpha-ketoacid dehydrogenase complex to prevent accumulation of branched-chain amino acids. Likewise, the increase in branched-chain amino acids caused by body wasting during starvation and uncontrolled diabetes is blunted by activation of the hepatic branched-chain alpha-ketoacid dehydrogenase complex. The activity state of the complex is regulated in the short term by the concentration of branched-chain alpha-ketoacids (inhibitors of branched-chain alpha-ketoacid dehydrogenase kinase) and in the long term by alteration in total branched-chain alpha-ketoacid dehydrogenase kinase activity. cDNAs have been cloned and the primary structure of the mature proteins deduced for the E1 alpha subunit of the human and rat liver branched-chain alpha-ketoacid dehydrogenase complex. The cDNA and protein sequences are highly conserved for the two species. Considerable sequence similarity is also apparent between the E1 alpha subunits of the human branched-chain alpha-ketoacid dehydrogenase complex and the pyruvate dehydrogenase complex. Maple syrup urine disease is caused by an inherited deficiency in the branched-chain alpha-ketoacid dehydrogenase complex. The molecular basis of one maple syrup urine disease family has been determined for the first time. The patient was found to be a compound heterozygote, inheriting an allele encoding an abnormal E1 alpha from the father, and an allele which is not expressed from the mother. The only known animal model for the disease (Polled Hereford cattle) has also been characterized. The mutation in these animals introduces a stop codon in the leader peptide of the E1 alpha subunit, resulting in premature termination of translation. Two thiamine responsive patients have been studied. The deduced amino acid sequences of the mature E1 alpha subunit and its leader sequence were normal, suggesting that the defect in these patients must exist in some other subunit of the complex. 3-Hydroxyisobutyrate dehydrogenase and methylmalonate-semialdehyde dehydrogenase, two enzymes of the valine catabolic pathway, were purified from liver tissue and characterized.(ABSTRACT TRUNCATED AT 400 WORDS)

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1990

[Interaction of quartz with human erythrocyte membrane--major protein changes and the effect of aluminium citrate].

The changes of the major proteins of human erythrocyte membrane by quartz were analysed by SDS-polyacrylamide gel electrophoresis. The relative mobility of proteins remained unchanged, whilst the relative abundance of Band 3 and PAS-1 proteins decreased (stained with Coomassie blue and PAS). The adsorption of Band 3 on to quartz were dose- and time-dependent. Aluminium citrate can inhibit the quartz adsorptive activity. The results support that the membrane damage of quartz is related to interacting with Band 3 proteins.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1990

Effects of purified compound (8501) on hyperlipidemia and the balance between thromboxane A2 and prostacyclin in rabbits.

New Zealand strain white male rabbits were divided into four groups to study the effects of 8501, extracted from a Chinese herb, on hyperlipidemia and the TXA2/PGI2 ratio in atherosclerotic rabbits. The results indicate that serum cholesterol and the levels of cholesterol and cholesteryl ester in aortic tissue were significantly increased in cholesterol-fed rabbits. The percentage of alpha-lipoprotein was significantly decreased and the aortic atherosclerotic plaque area was significantly increased. The data also demonstrate that the level of plasma TXB2 was markedly increased, while that of 6-keto-PGF1 alpha was significantly decreased. The TXB2/6-keto-PGF1 alpha ratio (T/6) was significantly increased. The decrease of 6-keto-PGF1 alpha occurred prior to the increase of TXB2. Compound 8501 not only lowered serum total cholesterol and aortic total cholesterol and cholesteryl ester but also antagonized the decrease of alpha-lipoprotein and atherosclerotic plaque formation. In addition, 8501 prevented the decrease of plasma 6-keto-PGF1 alpha and the increase of TXB2, and so the T/6 ratio was significantly decreased.

6-Ketoprostaglandin F1 alpha↗
PubMed1990

Sequence of the E1 alpha subunit of branched-chain alpha-ketoacid dehydrogenase in two patients with thiamine-responsive maple syrup urine disease.

Some patients with maple syrup urine disease respond to thiamine administration with a reduction in ketoaciduria and increase in activity of branched-chain alpha-ketoacid dehydrogenase. The biochemical mechanism underlying this effect is unknown but may result from decreased affinity of the mutant enzyme for thiamine or from stabilization of the abnormal enzyme by thiamine. The E1 alpha subunit of the complex participates in the thiamine-dependent decarboxylation of branched-chain alpha-ketoacids. We sequenced the E1 alpha subunit by using reverse transcription of RNA followed by enzymatic amplification of cDNA in two patients with thiamine-responsive maple syrup urine disease. The deduced amino acid sequence of this subunit in the patients was identical to that in normal controls, suggesting that in the patients the thiamine-binding site is abnormal because of a mutation in the E1 beta subunit. Other possible explanations are (a) that a mutation in the E1 beta or E2 subunits either alters thiamine binding by E1 alpha because of allosteric interactions or causes the complex to be unstable and (b) that thiamine stabilizes the complex.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1989

Cloning and sequence analysis of a cDNA for 3-hydroxyisobutyrate dehydrogenase. Evidence for its evolutionary relationship to other pyridine nucleotide-dependent dehydrogenases.

A 1.7-kilobase pair cDNA clone encoding 3-hydroxyisobutyrate dehydrogenase has been isolated by screening a rat liver lambda gt11 library with a 17-base oligonucleotide probe which corresponds to a portion of the N-terminal amino acid sequence of rabbit liver 3-hydroxyisobutyrate dehydrogenase. The cDNA contains an open reading frame of 1038 base pairs which includes an amino acid sequence that matches the N-terminal 35 amino acid sequence of rabbit 3-hydroxyisobutyrate dehydrogenase at 33 residues. The cDNA predicts a 300-amino acid mature protein with an amino acid composition and molecular weight very similar to that of rabbit liver 3-hydroxyisobutyrate dehydrogenase. Northern blot analysis of total RNA from several rat tissues shows an mRNA of approximately 2.0 kilobase pairs in each tissue. Relative mRNA levels were: kidney greater than liver = heart greater than muscle. The amino acid sequence of 3-hydroxyisobutyrate dehydrogenase shows similarity to several other pyridine nucleotide-dependent dehydrogenases. The resemblance to malate and lactate dehydrogenases suggests that the nucleotide-binding domain is located in the N-terminal region of the protein.

Alcohol Oxidoreductases↗
PubMed1989

A study of the reliability of clinical palpation of the spleen.

Clinical palpation of the spleen was assessed by reference to a radionuclide scan method for measuring spleen volume in vivo from V = 9.88A - 534, where V = volume (cm3) and A = posterior scan area (cm2) (Zhang & Lewis 1987). The position of the spleen tip in relation to the costal margin correlated well with clinical palpability when the spleen was clearly enlarged, but when the spleen tip was just below the costal margin it was not always palpable. In some cases a normal-sized spleen was palpable, whereas a non-palpable spleen was not always normal sized. As the scanning method gives an accurate measurement of spleen size it is especially useful in lesser degrees of enlargement when reliable information on the splenomegaly may help to elucidate a diagnosis and problems of management.

Adolescent↗
PubMed1989

The splenomegaly of myeloproliferative disorders: effects on blood volume and red blood count.

By means of a scintigraphic method for estimation of spleen size, the relationship was studied between spleen size and anaemia, total blood volume and red cell volume in patients with myeloproliferative disorders. There was significant correlation between spleen size and Hb, RBC and PCV in myelofibrosis. The size of the enlarged spleen did not, however, correlate with the degree of anaemia in the leukaemias. There was positive correlation between spleen size and red cell volume in these conditions. It was not possible to evaluate the severity of polycythaemia from spleen size and the degree of enlargement of the spleen does not appear to be a reliable parameter for staging and deciding on treatment in patients with PPP.

Anemia↗
PubMed1989

The splenomegaly of myeloproliferative and lymphoproliferative disorders: splenic cellularity and vascularity.

Employing radionuclide scanning, the volume of the spleen, its red cell pool and plasma pool have been measured in vivo, and the relative proportions of cellularity and vascularity of the spleen have been calculated in 51 patients with myeloproliferative and lymphoproliferative disorders. In primary proliferative polycythaemia (polycythaemia vera), the increase of spleen size was attributed mainly to the increase of splenic vascularity; in myelofibrosis and in hairy cell leukaemia, the increase of spleen size was associated with increase in both splenic vascularity and cellularity, whilst in CGL and CLL the increase was attributed more to cellularity than to vascularity.

Female↗
PubMed1989

cDNA cloning of the E1 alpha subunit of the branched-chain alpha-keto acid dehydrogenase and elucidation of a molecular basis for maple syrup urine disease.

We have cloned cDNAs encoding human and rat liver BCKDH E1 alpha subunits and deduced the primary structure of the mature protein. The sequences of the cDNA and protein are highly conserved between the two species. Significant sequence similarity has also been found between human BCKDH and PDH E1 alpha subunits. We have studied the molecular basis of MSUD by determining the enzyme activity and levels of BCKDH protein and mRNA, and by enzymatic amplification and sequencing of BCKDH E1 alpha-specific mRNA, from an MSUD patient and his parents. Different mutant alleles were identified in the two parents. The patient was a compound heterozygote, inheriting an allele encoding an abnormal E1 alpha from the father and an allele containing a defect in regulation from the mother. Our results demonstrate that a case of MSUD was caused by structural and regulatory mutations involving the E1 alpha subunit.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1989

Nutritional and hormonal regulation of the activity state of hepatic branched-chain alpha-keto acid dehydrogenase complex.

The hepatic branched-chain alpha-keto acid dehydrogenase complex plays an important role in regulating branched-chain amino acid levels. These compounds are essential for protein synthesis but are toxic if present in excess. When dietary protein is deficient, the hepatic enzyme is present in the inactive, phosphorylated state to allow conservation of branched-chain amino acids for protein synthesis. When dietary protein is excessive, the enzyme is in the active, dephosphorylated state to commit the excess branched-chain amino acids to degradation. Inhibition of protein synthesis by cycloheximide, even when the animal is starving for protein, results in activation of the hepatic branched-chain alpha-keto acid dehydrogenase complex to prevent accumulation of branched-chain amino acids. Likewise, the increase in branched-chain amino acids caused by body wasting during starvation and uncontrolled diabetes is blunted by activation of the hepatic branched-chain alpha-keto acid dehydrogenase complex. The activity state of the hepatic branched-chain alpha-keto acid dehydrogenase complex is regulated in the short term by the concentration of branched-chain alpha-keto acids (inhibitors of branched-chain alpha-keto acid dehydrogenase kinase) and in the long term by alteration in the total branched chain alpha-keto acid dehydrogenase kinase activity.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗