Induction of chalcone isomerase in elicitor-treated bean cells. Comparison of rates of synthesis and appearance of immunodetectable enzyme

Chalcone isomerase, an enzyme involved in the formation of flavonoid-derived compounds in plants, has been purified nearly 600-fold from cell suspension cultures of dwarf French bean (Phaseolus vulgaris L.). Chromatofocussing yielded a single form of the enzyme of apparent pI 5.0. This preparation was used to raise rabbit anti-(chalcone isomerase) serum. Changes in the rate of synthesis of chalcone isomerase have been investigated by indirect immunoprecipitation of enzyme labelled in vivo with [35S]methionine in elicitor-treated cultures of P. vulgaris. Elicitor, heat-released from cell walls of the phytopathogenic fungus Colletotrichum lindemuthianum, the causal agent of anthracnose disease of bean, causes increased synthesis of the isomerase, with maximum synthetic rate occurring 11-12 h after exposure to elicitor. Immune blotting studies indicate that the elicitor-mediated increase in extractable activity of the isomerase is associated with increased appearance of immunodetactable isomerase protein of Mr 27 000. However, the maximum level of immunodetectable isomerase was attained approximately 6 h earlier than maximum extractable activity. Furthermore, a 2.8-fold increase in enzyme activity above basal levels at 12 h after elicitor-treatment was associated with a corresponding 5.8-fold increase in immunodetectable enzyme. It is concluded that elicitor induces the synthesis of both active and inactive chalcone isomerase of Mr 27 000, and that some activation of inactive enzyme occurs during the elicitor-mediated increase in isomerase activity. The presence of a pool of inactive chalcone isomerase in bean cell cultures has recently been suggested on the basis of density labelling experiments utilising 2H from 2H2O [Dixon et al. (1983) Planta (Berl.) 159, 561-569].     

Production of L-ribose from L-ribulose by a triple-site variant of mannose-6-phosphate isomerase from Geobacillus thermodenitrificans

A triple-site variant (W17Q N90A L129F) of mannose-6-phosphate isomerase from Geobacillus thermodenitrificans was obtained by combining variants with residue substitutions at different positions after random and site-directed mutagenesis. The specific activity and catalytic efficiency (k(cat)/K(m)) for L-ribulose isomerization of this variant were 3.1- and 7.1-fold higher, respectively, than those of the wild-type enzyme at pH 7.0 and 70°C in the presence of 1 mM Co(2+). The triple-site variant produced 213 g/liter l-ribose from 300 g/liter L-ribulose for 60 min, with a volumetric productivity of 213 g liter(-1) h(-1), which was 4.5-fold higher than that of the wild-type enzyme. The k(cat)/K(m) and productivity of the triple-site variant were approximately 2-fold higher than those of the Thermus thermophilus R142N variant of mannose-6-phosphate isomerase, which exhibited the highest values previously reported.     

Transport ATPases in the erythrocytes of rats acclimatized to intermittent altitude hypoxia

The activity of Na+/K+- and Ca2+-ATPase and some allosteric properties of Na+/K+-ATPase were studied in whole erythrocytes and their membrane preparations (ghosts) from rats exposed to intermittent altitude hypoxia (10 and 24 exposures, 8 h/day in an altitude chamber, stepwise up to an altitude of 7,000 m). Ca2+-ATPase activity was increased both in whole erythrocytes and ghosts after the first phase of acclimatization (10 exposures). In a standard incubation medium (containing 3 mmol.l-1 MgCl2 ), Na+/K+-ATPase activity in the ghosts was also increased after the initial phase of acclimatization whereas in whole erythrocytes Na+/K+-ATPase was only decreased in the regression phase. At high MgCl2 concentrations (12 mmol.l-1) changes of Na+/K+-ATPase activity both in whole erythrocytes and in the ghosts followed similar time course with a pronounced increase in the first phase of acclimatization (10 exposures) followed by an abrupt drop (24 exposures) and then by a gradual normalization in the regression phase. Sensitivity of the enzyme to mounting MgCl2 concentrations was increased in the ghosts at the end of acclimatization and was decreased in whole erythrocytes during acclimatization and especially in the regression phase. It has been suggested that chronic altitude hypoxia leads to the alteration of cooperative interaction of the Na+/K+-ATPase subunits in the erythrocyte membrane and accumulation of some factor in the cells inhibiting this enzyme.     

The tryptic peptides of rabbit muscle triose phosphate isomerase

1. The peptides obtained by tryptic digestion of S-[(14)C]carboxymethylated rabbit muscle triose phosphate isomerase have been studied. 2. The first step in the fractionation of the tryptic digest was gel filtration on coupled columns of Sephadex G-25 and G-50. Further fractionation was carried out by paper electrophoresis and paper chromatography. 3. The digest contained 26 peptides and three free amino acids. The sizes of the peptides ranged from two to 29 residues. 4. The sequences of the peptides have been determined. 5. The length of the polypeptide chains is about 250 amino acid residues. 6. The variant sequences encountered were due to partial deamidation; this may be one of the reasons for multiple forms of the enzyme. 7. The chicken and rabbit enzymes are compared. 8. Detailed evidence for the sequences of the tryptic peptides has been deposited as Supplementary Publication SUP 50024 at the British Library, Lending Division (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms given in Biochem. J. (1973) 131, 5.     

Biochemical and molecular study of mentally retarded patient with partial deficiency of hypoxanthine-guanine phosphoribosyltransferase

Nucleotide metabolism was studied in erythrocytes of a mentally retarded child and family members. Partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency was found in the propositus and an asymptomatic maternal uncle. Studies in crude lysates demonstrated decreased apparent V(max) and slightly decreased apparent K(m) for hypoxanthine in both HPRT-deficient subjects. Genomic DNA analysis revealed a single nucleotide change with leucine-147 to phenylalanine substitution in both subjects; mother and grandmother were heterozygous carriers of the same defect. This new variant has been termed HPRT(Potenza). Increased erythrocyte concentration of NAD and rate of synthesis by intact erythrocytes were found in the patient; increased activities of nicotinic acid phosphoribosyltransferase (NAPRT) and NAD synthetase (NADs) were demonstrated in erythrocyte lysates, with normal apparent K(m) for their substrates and increased V(max). These alterations were not found in any member of the family, including the HPRT-deficient uncle. These findings show multiple derangement of nucleotide metabolism associated with partial HPRT deficiency. The enzyme alteration was presumably not the cause of neurological impairment since no neurological symptoms were found in the HPRT-deficient uncle, whereas they were present in the propositus' elder brother who had normal HPRT activity.     

Chronic nonspherocytic hemolytic anemia (CNSHA) and glucose 6 phosphate dehydrogenase (G6PD) deficiency in a patient with familial amyloidotic polyneuropathy (FAP)

Summary A new glucose-6-phosphate dehydrogenase (G6PD) variant with severe erythrocytic G6PD deficiency and a unique pH optimum is described in a young patient with chronic nonspherocytic hemolytic anemia (CNSHA) and familial amyloidotic polyneuropathy (FAP). Chronic hemolysis was present in the absence of infections, oxidant drugs or ingestion of faba beans. Residual enzyme activity was about 2.6% and 63% of normal activity in erythrocytes and leucocytes, respectively. A molecular study using standard methods showed G6PD in the patient to have normal electrophoretic mobility (at pH 7.0, 8.0 and 8.8), normal apparent affinity for substrates (K_m, G6P and NADP) and a slightly abnormal utilization of substrate analogues (decreased deamino-NADP and increased 2-deoxyglucose-6-phosphate utilization). Heat stability was found to be markedly decreased (8% of residual activity after 20 min of incubation at 46°C) and a particular characteristic of this enzyme was a biphasic pH curve with a greatly increased activity at low pH. Although molecular characteristics of this variant closely resemble those of G6PD Bangkok and G6PD Duarte, it can be distinguished from these and all other previously reported variants by virtue of its unusual pH curve. Therefore the present variant has been designated G6PD Clinic to distinguish it from other G6PD variants previously described.     

Rabbit phosphoglucose isomerase/neuroleukin/autocrine motility factor: cloning via interspecies identity

Phosphoglucose isomerase is the first committed enzyme of glycolysis. The protein also has a variety of biological activities on mammalian cells. The molecular basis of these extracellular functions is unclear, and the high resolution three-dimensional structure of a mammalian enzyme has not been described. We report here the cDNA and protein sequence for phosphoglucose isomerase from rabbit muscle. The sequence was obtained directly by PCR without the need to screen clones from a cDNA library and encoded active enzyme when expressed in bacterial cells. The 558 amino acid rabbit coding sequence is the same length as and highly similar (92% residue identity) to the sequences from human and pig and less so (88%) to the mouse enzyme. Non-conservative amino acid changes between the four mammalian sequences are concentrated in the first 35 and last five residues. The rabbit protein has an additional Cys residue and amino acid changes at five positions otherwise invariant in the mammalian enzymes.     

Glucosephosphate isomerase from Trypanosoma brucei. Cloning and characterization of the gene and analysis of the enzyme

In Trypanosoma brucei the enzyme glucose-6-phosphate isomerase, like most other enzymes of the glycolytic pathway, resides in a microbody-like organelle, the glycosome. Here we report a detailed study of this enzyme, involving a determination of its kinetic properties and the cloning and sequence analysis of its gene. The gene codes for a polypeptide of 606 amino acids, with a calculated Mr of 67280. The protein predicted from the gene sequence has 54-58% positional identity with its yeast and mammalian counterparts. Compared to those other glucose-6-phosphate isomerases the trypanosomal enzyme contains an additional 38-49 amino acids in its N-terminal domain, as well as a number of small insertions and deletions. The additional amino acids are responsible for the 5-kDa-larger subunit mass of the T. brucei enzyme, as measured by gel electrophoresis. The glucose-6-phosphate isomerase of the trypanosome has no excess of positive residues and, consequently, no high isoelectric point, in contrast to the other glycolytic enzymes that are present in the glycosome. However, similar to other glycosomal proteins analyzed so far, specific clusters of positive residues can be recognized in the primary structure. Comparison of the kinetic properties of the T. brucei glucose-6-phosphate isomerase with those of the yeast and rabbit muscle enzymes did not reveal major differences. The three enzymes have very similar pH profiles. The affinity for the substrate fructose 6-phosphate (Km = 0.122 mM) and the inhibition constant for the competitive inhibitor gluconate 6-phosphate (Ki = 0.14 mM) are in the same range as those of the similar enzymes. The Km shows the same strong dependence on salt as the rabbit muscle enzyme, although somewhat less than the yeast glucose-6-phosphate isomerase. The trypanocidal drug suramin inhibits the T. brucei and yeast enzymes to the same extent (Ki = 0.29 and 0.36 mM, respectively), but it had no effect on the rabbit muscle enzyme. Agaricic acid, a potent inhibitor of various glycosomal enzymes of T. brucei, has also a strong, irreversible effect on glucose-6-phosphate isomerase, while leaving the yeast and mammalian enzymes relatively unaffected.     

Glucose-6-phosphate dehydrogenase (G6PD) Iserlohn and G6PD Regensburg: two new severe enzyme defects in German families

Two new inheritable variants of glucose-6-phosphate dehydrogenase have been found in two unrelated German families. Patients with one variant (G6PD Iserlohn, also referred to as G6PD I) suffered from intermittent hemolytic crises caused by fava beans; patients with the other variant (G6PD Regensburg, G6PD II) disclosed chronic nonspherocytic hemolytic anemia aggravated by drug treatment. Due to their unusual biochemical characteristics, the new variants were designated G6PD Iserlohn and G6PD Regensburg. Both variants showed a reduction of enzyme activity to about 6% of the normal in erythrocytes, normal electrophoretic mobility, increased affinity for glucose-6-phosphate, a reduced affinity for NADP and a pH optimum in the neutral region (7.0 and 7.5). G6PD Iserlohn had a decreased affinity for the inhibitor NADPH; G6PD Regensburg had a normal inhibitor constant. Deamino NADP was utilized at an increased rate by G6PD Regensburg. G6PD Iserlohn was thermostable, G6PD Regensburg mildly instable. G6PD activity in leukocytes was normal in G6PD Iserlohn and reduced to the same degree as in erythrocytets in G6PD Regensburg. The cause of the decreased activity of G6PD Iserlohn appears to be in vivo instability; in G6PD Regensburg further mechanisms might include reduced specific activity or reduced synthesis of the variant enzyme.     

Cyclic AMP-dependent phosphorylation of erythrocyte variant pyruvate kinase

Cyclic AMP-dependent phosphorylation of a variant erythrocyte pyruvate kinase (PK; EC 2.7.1.40) was studied. This variant PK shows a faster electrophoretic mobility than the normal enzyme. The decreased enzyme activity observed in this variant is associated with a quantitative decrease of enzyme protein. Other parameters are within normal ranges. The partially purified variant PK is phosphorylated with a subsequent increase of k0.5s (phosphoenolpyruvate) similar to the normal control, suggesting that the structural abnormality of the variant enzyme has no influence on the phosphorylation-deactivation mechanism. On the other hand, the variant PK in the erythrocyte was less extensively phosphorylated than PK in normal erythrocytes. This may be the result of abnormal metabolism in the patient's red cells, including increased 2,3-diphosphoglycerate and decreased adenosine triphosphate levels.     

Isolation of rabbit muscle glucosephosphate isomerase by a single-step substrate elution.

A simple method has been developed for the rapid isolation of crystalline glucosephosphate isomerase (EC 5.3.1.9) from rabbit muscle. The enzyme is first bound to cellulose phosphate by adding the ion exchanger to a solution of the crude tissue extract. After filtering and washing the cellulose with buffer, the isomerase is specifically eluted in a batch process by its substrate, glucose 6-phosphate. The entire procedure is very rapid and results in a good recovery (at least 50%) of the enzyme with specific activity of approximately 900 units per mg. The enzyme is homogeneous by polyacrylamide gel electrophoresis in the presence of absence of sodium dodecyl sulfate and by analytical ultracentrifugation.     

The amino acid sequence of rabbit muscle triose phosphate isomerase.

The amino acid sequence of rabbit muscle triose phosphate isomerase was deduced by characterizing peptides that overlap the tryptic peptides. Thiol groups were modified by oxidation, carboxymethylation or aminoen. About 50 peptides that provided information about overlaps were isolated; the peptides were mostly characterized by their compositions and N-terminal residues. The peptide chains contain 248 amino acid residues, and no evidence for dissimilarity of the two subunits that comprise the native enzyme was found. The sequence of the rabbit muscle enzyme may be compared with that of the coelacanth enzyme (Kolb et al., 1974): 84% of the residues are in identical positions. Similarly, comparison of the sequence with that inferred for the chicken enzyme (Furth et al., 1974) shows that 87% of the residues are in identical positions. Limited though these comparisons are, they suggest that triose phosphate isomerase has one of the lowest rates of evolutionary change. An extended version of the present paper has been deposited as Supplementary Publication SUP 50040 (42 pages) at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms given in Biochem. J. (1975) 145, 5.     

Phosphohexose isomerase polymorphism in the domestic cat

Genetic variation of the enzyme phosphohexose isomerase (PHI) has been found in the erythrocytes of Australian domestic cats by horizontal starch gel electrophoresis at pH 8.2. Three complex patterns of isoenzymes, designated F, FS and S, were obtained migrating anodally. Limited family studies and the distribution of the three main phenotypes indicated that the polymorphism is controlled by two codominant autosomal alleles, PHI^F and PHI^S Gene frequencies for PHI^F and PHI^S have been calculated as 0.036 and 0.964 respectively. Three additional variant forms have also been observed.     

Cell age dependent decay of human erythrocytes glucose-6-phosphate isomerase

Glucose-6-phosphate isomerase shows a biphasic decay pattern during red blood cell aging, which is very fast during the first part of cell's life span in circulation. This decay is not due to accumulation of inactive enzyme molecules, as shown by immunological studies, but is accompanied by the formation of secondary isozymes (i.e., chemically modified forms). Electrophoretic and ion-exchange chromatographic experiments show that glucose-6-phosphate isomerase (D-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9) consists of only one isozymic form in young erythrocytes but is present in two components, with different electric charge, in mature and old cells. This secondary isozyme is more stable to heat treatment and is inactivated by IgG anti-glucose-6-phosphate isomerase with a lower affinity than the native isozyme. In vitro incubation of homogeneous human glucose-6-phosphate isomerase under conditions known to produce enzyme deamination does not reproduce the isozymic pattern found in erythrocytes, suggesting that one or more mechanisms other than those previously described to explain glucose-6-phosphate isomerase microheterogeneity occur in the human erythrocyte.     

Clinical symptoms and biochemical properties of three new glucosephosphate isomerase variants

Glucosephosphate isomerase deficiency as the cause of macrocytic congenital nonspherocytic hemolytic anemia is described in three unrelated families. The biochemical properties of the variant glucosephosphate isomerases indicate that the patients have new variants, designated as GPI Kiel, GPI Hamburg, and GPI Homburg. The severity of the clinical symptoms depended on the amount of residual GPI activity and the biochemical properties of the variant enzyme. Thus the patient with GPI Kiel (34% residual activity) whose variant GPI was slightly unstable showed a mild chronic hemolytic anemia. The patient with GPI Homburg (7% residual activity) whose variant enzyme was stable and had a reduced specific activity, suffered from severe congenital hemolytic anemia and neuromuscular symptoms. Due to the special properties of GPI Homburg, we assume that both the hematological and neuromuscular symptoms of the patient with GPI Homburg are caused by his GPI deficiency. The twins with GPI Hamburg (27% residual activity) had a distinctly unstable variant enzyme and had suffered from hemolytic crises since birth. Only GPI Homburg showed an altered electrophoretic mobility and an increased affinity for fructose-6-phosphate. The other two variants had normal values.     

Structure/function relationships responsible for the kinetic differences between human type 1 and type 2 3beta-hydroxysteroid dehydrogenase and for the catalysis of the type 1 activity

Two distinct genes encode the 93% homologous type 1 (placenta, peripheral tissues) and type 2 (adrenals, gonads) 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD/isomerase) in humans. Mutagenesis studies using the type 1 enzyme have produced the Y154F and K158Q mutant enzymes in the Y(154)-P-H(156)-S-K(158) motif as well as the Y269S and K273Q mutants from a second motif, Y(269)-T-L-S-K(273), both of which are present in the primary structure of the human type 1 3beta-HSD/isomerase. In addition, the H156Y mutant of the type 1 enzyme has created a chimera of the type 2 enzyme motif (Y(154)-P-Y(156)-S-K(158)) in the type 1 enzyme. The mutant and wild-type enzymes have been expressed and purified. The K(m) value of dehydroepiandrosterone is 13-fold greater, and the maximal turnover rate (K(cat)) is 2-fold greater for wild-type 2 3beta-HSD compared with the wild-type 1 3beta-HSD activity. The H156Y mutant of the type 1 enzyme has substrate kinetic constants for 3beta-HSD activity that are very similar to those of the wild-type 2 enzyme. Dixon analysis shows that epostane inhibits the 3beta-HSD activity of the wild-type 1 enzyme with 14-17-fold greater affinity compared with the wild-type 2 and H156Y enzymes. The Y154F and K158Q mutants exhibit no 3beta-HSD activity, have substantial isomerase activity, and utilize substrate with K(m) values similar to those of wild-type 1 isomerase. The Y269S and K273Q mutants have low, pH-dependent 3beta-HSD activity, exhibit only 5% of the maximal isomerase activity, and utilize the isomerase substrate very poorly. From these studies, a structural basis for the profound differences in the substrate and inhibition kinetics of the wild-type 1 and 2 3beta-HSD, plus a catalytic role for the Tyr(154) and Lys(158) residues in the 3beta-HSD reaction have been identified. These advances in our understanding of the structure/function of human type 1 and 2 3beta-HSD/isomerase may lead to the design of selective inhibitors of the type 1 enzyme not only in placenta to control the onset of labor but also in hormone-sensitive breast, prostate, and choriocarcinoma tumors to slow their growth.     

Mannose-6-phosphate isomerase polymorphism in baboon erythrocytes

Although erythrocytic mannose-6-phosphate isomerase (MPI) has been reported to be undetectable in mammals, we have demonstrated that sufficient activity is present in some species to enable its electrophoretic analysis. A survey of MPI from 2656 baboons revealed four allelic isozymes which segregated codominantly in pedigreed families. The gene frequencies differed significantly among five subspecies of baboons. However, the MPI*C allele had the highest frequency in all subspecies, ranging from 0.830 to 1.000. MPI phenotypes from erythrocytes and liver of the same individual were identical, indicating that the erythrocytic enzyme is specified by the same gene locus as the liver enzyme.     

Characterization of a phosphoglycerate kinase deficiency variants not associated with hemolytic anemia.

The properties of a variant phosphoglycerate kinase (PGK) found in a large German clan were examined. The normal and variant enzymes, isolated by affinity chromatography, have the same molecular weight, specific activity, substrate affinity, and nearly identical pH-optima. Using immunoinactivation and immunodiffusion, the same specific activity for both forms was again determined. Since the enzymatic activity in older and younger erythrocytes varied only slightly, and since the specific activity of the variant was normal, the variant seems to be stable in vivo. This suggests that the decreased enzyme content is due to a decreased synthesis rate. The variant PGK described here is distinctly different from the known PGK variants and has been designated as "PGK München."     

A monoclonal antibody against horse kidney (Na+ + K+)-ATPase inhibits sodium pump and E2K to E1 conversion of (Na+ + K+)-ATPase from outside of the cell membrane

Monoclonal antibodies against horse kidney outer medulla (Na+ + K+)-ATPase were prepared. One of these antibodies (M45-80), was identified as an IgM, recognized the alpha subunit of the enzyme. M45-80 had the following effects on horse kidney (Na+ + K+)-ATPase: (1) it inhibited the enzyme activity by 50% in 140 mM Na+ and by 80% in 8.3 mM Na+; (2) it increased the Na+ concentration necessary for half-maximal activation (K0.5 for Na+) from 12.0 to 57.6 mM, but did not affect K0.5 for K+; (3) it slightly increased the K+-dependent p-nitrophenylphosphatase (K-pNPPase) activity; (4) it inhibited phosphorylation of the enzyme with ATP by 30%, but did not affect the step of dephosphorylation; and (5) it enhanced the ouabain binding rate. These data are compatible with a stabilizing effect on the E2 form of (Na+ + K+)-ATPase. M45-80 was concluded to bind to the extracellular surface of the plasmamembrane, based on the following evidence: (1) M45-80 inhibited by 50% the ouabain-sensitive 86Rb+ uptake in human intact erythrocytes from outside of the cells; (2) the inhibition of (Na+ + K+)-ATPase activity in right-side-out vesicles of human erythrocytes was greater than that in inside-out vesicles; and (3) the fluorescence intensity due to FITC-labeled rabbit anti-mouse IgM that reacted with M45-80 bound to the right-side-out vesicles was much greater than that in the case of the inside-out vesicles.     

Characterization of two new electrophoretic variants of human triosephosphate isomerase: Stability,kinetic, and immunological properties

Two new electrophoretic variants of human triosephosphate isomerase (TPI) have been partially purified and characterized. The TPI Manchester variant, a cathodally migrating electrophoretic allozyme identified in an individual with the phenotype TPI 1-Manchester, is associated with a normal level of enzyme activity in erythrocytes and normal kinetic properties. It is very thermolabile at 55 and 57° C, although it is not uniquely sensitive to either guanidine-HCl or urea denaturation. The TPI Hiroshima-2 variant is an anodally migrating allozyme (the phenotype of proband is TPI 1-Hiroshima-2) with normal activity and kinetic properties and also normal stability characteristics. It is inactivated less by antisera raised against normal human TPI than either the normal or the Manchester allozyme. Dissociation-reassociation experiments utilizing these allozymes have confirmed that normal human red blood cell TPI isozymes are produced by a sequence of reactions (presumably deamidations) involving alternating subunits.Financial support was derived from Contract EY-77-C-02-2828 from the Department of Energy.