Detection of mammaglobin in the sera of patients with breast cancer

Current procedures for the diagnosis of breast cancer are cumbersome and invasive, making detection of this disease difficult. A rapid screening test for early detection of breast cancer would allow for better management of this deadly disease. In this report, we show that, with the exception of the skin, mammaglobin mRNA is specifically expressed in mammary tissue and commonly overexpressed in breast cancer. Mammaglobin is not expressed in other types of cancer including colon, lung, ovarian, and prostate cancer. Breast-specific expression of mammaglobin protein was shown using immunohistochemical methods. Mammaglobin is secreted from both established breast cancer cell lines and primary breast carcinoma cells cultured in vitro. Using a monoclonal antibody-based assay for monitoring the presence of mammaglobin in serum, elevated levels of mammaglobin were detected in sera of patients with breast cancer, but not in healthy women. Thus, mammaglobin, which is overexpressed and secreted from breast carcinoma cells, is detectable in sera of patients with breast cancer and may provide a rapid screening test for the diagnosis and management of breast cancer.

Serological expression cloning and immunological evaluation of MTB48, a novel Mycobacterium tuberculosis antigen

Improved diagnostics are needed for the detection of Mycobacterium tuberculosis, especially for patients with smear-negative disease. To address this problem, we have screened M. tuberculosis (H37Rv and Erdman strains) genomic expression libraries with pooled sera from patients with extrapulmonary disease and with sera from patients with elevated reactivity with M. tuberculosis lysate. Both serum pools were reactive with clones expressing a recombinant protein referred to here as MTB48. The genomic sequence of the resulting clones was identical to that of the M. tuberculosis H37Rv isolate and showed 99% identity to the Mycobacterium bovis and M. bovis BCG isolate sequences. The genomic location of this sequence is 826 bp upstream of a region containing the esat-6 gene that is deleted in the M. bovis BCG isolate. The mtb48 1,380-bp open reading frame encodes a predicted 47.6-kDa polypeptide with no known function. Southern and Western blot analyses indicate that this sequence is present in a single copy and is conserved in the M. tuberculosis and M. bovis isolates tested but not in other mycobacterial species tested, including Mycobacterium leprae and Mycobacterium avium. In addition, the native protein was detected in the cytoplasm, as was a processed form that was also shed into the medium during culture. Serological analysis of recombinant MTB48 and the M. tuberculosis 38-kDa antigen with a panel of patient and control sera indicates that the inclusion of recombinant MTB48 in a prototype serodiagnostic test increases assay sensitivity for M. tuberculosis infection when it is combined with other known immunodominant antigens, such as the 38-kDa antigen.

Serodiagnosis of human granulocytic ehrlichiosis by using novel combinations of immunoreactive recombinant proteins

A panel of seven recombinant antigens, derived from Ehrlichia phagocytophila (the agent of human granulocytic ehrlichiosis), was evaluated by class-specific enzyme-linked immunosorbent assays (ELISAs) for utility in the diagnosis of the infection. Fourteen genomic fragments, obtained by serologic expression screening, contained open reading frames (ORFs) encoding 16 immunodominant antigens. Eleven of these antigens were members of the major surface protein (MSP) multigene family. Alignment of their predicted protein sequences revealed a pattern of conserved sequences, which contained short direct repeats, flanking a variable region. In addition, two genomic clones contained two and three MSP ORFs, respectively, indicating that these genes are clustered in tandem copies. The implications for this pattern of both genomic and protein arrangements in antigenic variations of MSPs and in their utilities in a diagnostic assay are discussed. In addition to two MSP recombinant antigens (rHGE-1 and -3) and a fusion protein of these antigens (rErf-1), five further recombinants were evaluated by ELISA. Two of these antigens (rHGE-14 and -15) were novel, while a third (rHGE-2), with no known function, has been described. The final two recombinant antigens (rHGE-9 and -17) represent overlapping segments of the ankyrin gene (ank). The addition of rHGE-9 ELISA data resulted in the detection of 78% (21 of 27) of acute-phase sera. When serologic data for all recombinants are combined, 96.2% (26 of 27) of convalescent-phase patient serum samples and 85.2% (23 of 27) of acute-phase patient serum samples are detected, indicating the potential of these antigens for use in the development of a rapid serologic assay for the detection of E. phagocytophila infection.

Transcriptional complementarity in breast cancer: application to detection of circulating tumor cells

BACKGROUND

We used a combination of genetic subtraction, silicon DNA microarray analysis, and quantitative PCR to identify tissue- and tumor-specific genes as diagnostic targets for breast cancer.

METHODS AND RESULTS

From a large number of candidate antigens, several specific subsets of genes were identified that showed concordant and complementary expression profiles. Whereas transcriptional profiling of mammaglobin resulted in the detection of 70% of tumors in a panel of 46 primary and metastatic breast cancers, the inclusion of three additional markers resulted in detection of all 46 specimens. Immunomagnetic epithelial cell enrichment of circulating tumor cells from the peripheral blood of patients with metastatic breast cancer, coupled with RT-PCR-based amplification of breast tumor-specific transcripts, resulted in the detection of anchorage-independent tumor cells in the majority of patients with breast cancer with known metastatic disease.

CONCLUSION

Complementation of mammaglobin with three additional genes in RT-PCR increases the detection of breast cancers in tissue and circulating tumor cells.

WT1-specific serum antibodies in patients with leukemia

WT1 is an oncogenic protein expressed by the Wilms' tumor gene and overexpressed in the majority of acute myelogenous leukemias (AMLs) and chronic myelogenous leukemias (CMLs). The current study analyzed the sera of patients with AML and CML for the presence of antibodies to full-length and truncated WT1 proteins. Sixteen of 63 patients (25%) with AML had serum antibodies reactive with WT1/full-length protein. Serum antibodies from all 16 were also reactive with WT1/NH2-terminal protein. By marked contrast, only 2 had reactivity to WT1/COOH-terminal protein. Thus, the level of immunological tolerance to the COOH terminus may be higher than to the NH2 terminus. The WT1/COOH-terminal protein contains four zinc finger domains with homology to other self-proteins. By implication, these homologies may be related to the increased immunological tolerance. Results in patients with CML were similar with antibodies reactive to WT1/full-length protein detectable in serum of 15 of 81 patients (19%). Antibodies reactive with WT1/NH2-terminal protein were present in the serum of all 15, whereas antibodies reactive with WT1/COOH-terminal protein were present in only 3. By contrast to results in leukemia patients, antibodies reactive with WT1/full-length protein were detected in only 2 of 96 normal individuals. The greater incidence of antibody in leukemia patients provides strong evidence that immunization to the WT1 protein occurred as a result of patients bearing malignancy that expresses WT1. These data provide further stimulus to test therapeutic vaccines directed against WT1 with increased expectation that the vaccines will be able to elicit and/or boost an immune response to WT1.

Identification and characterization of prostein, a novel prostate-specific protein

In this report, we describe the application of a systematic, genome-based approach to identify prostein, a novel prostate-specific protein expressed in normal and malignant prostate tissues. Characterization of the prostein gene shows that prostein cDNA encodes a 553-amino acid protein. The protein is predicted to be a type IIIa plasma membrane protein with a cleavable signal peptide and 11 transmembrane-spanning regions. The prostein gene is located on chromosome 1 at the WI-9641 locus between q32 and q42. Prostein mRNA is shown to be uniquely expressed in normal and cancerous prostate tissues using Northern blot, eDNA microarray, and real-time PCR analyses. Furthermore, prostein mRNA expression does not appear to be prostate tumor grade related and is restricted exclusively to prostate cell lines. Immunohistochemical staining using a mouse monoclonal antibody generated against prostein demonstrates that this protein is specifically detected in prostate tissues both at the plasma membrane and in the cytoplasm. Prostein expression is androgen responsive because treatment of LNCaP cells with androgen up-regulates prostein message and protein expression levels. These results validate prostein as a prostate-specific marker with potential utility in the diagnosis and treatment of prostate cancer.

Mass spectrometric identification of mtb81, a novel serological marker for tuberculosis

We have used serological proteome analysis in conjunction with tandem mass spectrometry to identify and sequence a novel protein, Mtb81, which may be useful for the diagnosis of tuberculosis (TB), especially for patients coinfected with human immunodeficiency virus (HIV). Recombinant Mtb81 was tested by an enzyme-linked immunosorbent assay to detect antibodies in 25 of 27 TB patients (92%) seropositive for HIV as well as in 38 of 67 individuals (57%) who were TB positive alone. No reactivity was observed in 11 of 11 individuals (100%) who were HIV seropositive alone. In addition, neither sera from purified protein derivative (PPD)-negative (0 of 29) nor sera from healthy (0 of 45) blood donors tested positive with Mtb81. Only 2 of 57 of PPD-positive individuals tested positive with Mtb81. Sera from individuals with smear-positive TB and seropositive for HIV but who had tested negative for TB in the 38-kDa antigen immunodiagnostic assay were also tested for reactivity against Mtb81, as were sera from individuals with lung cancer and pneumonia. Mtb81 reacted with 26 of 37 HIV(+) TB(+) sera (70%) in this group, compared to 2 of 37 (5%) that reacted with the 38-kDa antigen. Together, these results demonstrate that Mtb81 may be a promising complementary antigen for the serodiagnosis of TB.

Serological expression cloning of novel immunoreactive antigens of Babesia microti

Increased recognition of the prevalence of human babesiosis in the United States, together with rising concern about the potential for transmission of this infection by blood transfusion, has provided motivation to develop definitive serologic and molecular tests for the causative agent, Babesia microti. To develop more sensitive and specific assays for B. microti, we screened a genomic expression library with patient serum pools. This screening resulted in the identification of three classes of novel genes and an additional two novel, unrelated genes, which together encode a total of 17 unique B. microti antigens. The first class (BMN1-2 family) of genes encodes seven closely related antigens with a degenerate six-amino-acid repeat that shows limited homology to Plasmodium sp. merozoite and sporozoite surface antigens. A second class (BMN1-8 family) of genes encodes six related antigens, and the third class (BMN1-17 family) of genes encodes two related antigens. The two remaining genes code for novel and unrelated sequences. Among the three classes of antigens and remaining novel sequences, five were chosen to code for the most immunodominant antigens (BMN1-2, -9, -15, and -17 and MN-10). Western blot analysis with the resulting recombinant proteins indicated that these antigens were targets of humoral immune responses during B. microti infection in humans.

Identification of differentially expressed genes in human prostate cancer using subtraction and microarray

We have identified human prostate cancer- and tissue-specific genes using cDNA library subtraction in conjunction with high throughput microarray screening. Subtracted cDNA libraries of prostate tumors and normal prostate tissue were generated. Characterization of subtracted libraries showed enrichment of both cancer- and tissue-specific genes. Highly redundant clones were eliminated by colony hybridization. The remaining clones were selected for microarray to determine gene expression levels in a variety of tumor and normal tissues. Clones showing overexpression in prostate tumors and/or normal prostate tissues were selected and sequenced. Here we report the identification of two genes, P503S and P504S, from subtracted libraries and a third gene, P510S, by subtraction followed by microarray screening. Their expression profiles were further confirmed by Northern blot, real-time PCR (TaqMan), and immunohistochemistry to be overexpressed in prostate tissues and/or prostate tumors. Full-length cDNA sequences were cloned, and their subcellular locations were predicted by a bioinformatic algorithm, PSORT, to be plasma membrane proteins. The genes identified through these approaches are potential candidates for cancer diagnosis and therapy.

Multiepitope synthetic peptide and recombinant protein for the detection of antibodies to Trypanosoma cruzi in patients with treated or untreated Chagas' disease

A tetrapeptide and a recombinant protein, each representing 4 immunodominant epitopes of Trypanosoma cruzi, were tested by use of ELISA for the detection of serum antibodies. Sera from individuals with Chagas' disease, including persons untreated and successfully or unsuccessfully treated, were tested. These assays detected antibody in 100% of the parasitemias. The antibody reactivity decreased based on the success of treatment. Higher sensitivity was observed for tetrapeptide/recombinant protein assays than for lysate-based ELISA, and specificity was improved, particularly with Leishmania sera. The results indicate that multiepitope antigens provide a more sensitive and specific alternative to lysate for detection of anti-T. cruzi antibodies, as required for developing blood screening assays.

A polymorphic multigene family encoding an immunodominant protein from Babesia microti

Human babesiosis in the United States is caused predominantly by Babesia microti, a tick-transmitted blood parasite. Improved testing methods for the detection of infection with this parasite are needed, since asymptomatic B. microti infection represents a potential threat to the blood supply in areas where B. microti is endemic. We performed immunoscreening of an expression library of genomic DNA from a human isolate of B. microti (strain MN1). Among 17 unique immunoreactive clones, we identified 9 which represent a related family of genes with little sequence homology to other known sequences but with an architecture resembling that of several surface proteins of Plasmodium. Within this family, a tandem array of a degenerate six-amino-acid repeat (SEAGGP, SEAGWP, SGTGWP, SGTVGP) was found in various lengths between relatively well conserved segments at the N and C termini. In order to examine within-clone variation, we developed a PCR protocol for direct recovery of a specific bmn1-6 homologue directly from 30 human blood isolates, 4 corresponding hamster isolates, and 5 geographically corresponding Peromyscus leucopus (white-footed mouse) isolates. Isolates from the hamsters had the same sequences as those found in the corresponding human blood, suggesting that genetic variation of bmn1-6 does not occur during passage. However, clones from different patients were often substantially different from each other with regard to the number and location of the degenerate repeats within the bmn1-6 homologue. Moreover, we found that strains that were closely related geographically were also closely related at the sequence level; nine patients, all from Nantucket Island, Mass., harbored clones that were indistinguishable from each other but that were distinct from those found in other northeastern or upper midwestern strains. We conclude that considerable genetic and antigenic diversity exists among isolates of B. microti from the United States and that geographic clustering of subtypes may exist. The nature of the bmn1-6 gene family suggests a mechanism of antigenic variation in B. microti that may occur by recombination, differential expression, or a combination of both mechanisms.

A multi-epitope synthetic peptide and recombinant protein for the detection of antibodies to Trypanosoma cruzi in radioimmunoprecipitation-confirmed and consensus-positive sera

Peptide epitopes of Trypanosoma cruzi have been identified through expression cloning. A tripeptide (2/D/E) containing three epitopes (TcD, TcE, PEP-2) was used in ELISA to detect antibodies to T. cruzi in 239 of 240 consensus-positive sera and 41 of 42 sera confirmed positive by radioimmunoprecipitation assay. The 1 discrepant consensus-positive serum was used to expression-clone a novel gene that contained a repeat sequence. A peptide corresponding to this sequence, TcLo1.2, was specific for T. cruzi. This antigen detected the discrepant consensus-positive serum and enhanced reactivity of low-positive sera in the tripeptide assay. A branched synthetic peptide, 2/D/E/Lo1.2, or a linear recombinant, r2/D/E/Lo1.2, realized all of the diagnostic features of the four epitopes, including the ability to boost reactivity of low-reactive sera. These studies show that peptides and recombinants containing multiple repeat epitopes are powerful tools for developing assays for T. cruzi antibody detection and have direct application in blood screening.

A cloned antigen (recombinant K39) of Leishmania chagasi diagnostic for visceral leishmaniasis in human immunodeficiency virus type 1 patients and a prognostic indicator for monitoring patients undergoing drug therapy

Serologic assays using crude antigens for the diagnosis of visceral leishmaniasis in human immunodeficiency virus type 1 (HIV)-seropositive patients have been shown to lack sensitivity and specificity, particularly in AIDS patients. Antibodies to a cloned antigen, recombinant (r) K39, of Leishmania chagasi are specific for members of the Leishmania donovani complex and have been shown to indicate active disease in immunocompetent persons. This study demonstrated that antibodies to rK39 were also detectable in HIV-seropositive patients coinfected with Leishmania infantum. Furthermore, the rK39 ELISA was more sensitive than an IFA for detecting L. infantum infections in patients with AIDS. In addition, antibody titers to rK39 in HIV-negative patients infected with L. infantum or L. chagasi declined during treatment with meglumine antimoniate or liposomal amphotericin B. In contrast, most patients who clinically relapsed showed increased antibody titers to rK39. These data demonstrate the diagnostic and prognostic utility of rK39 in detecting active visceral leishmaniasis.

rK39: a cloned antigen of Leishmania chagasi that predicts active visceral leishmaniasis

The diagnosis of visceral leishmaniasis (VL), a serious and often fatal parasitic disease caused by members of the Leishmania donovani complex, remains problematic. Current methods rely on clinical criteria, parasite identification in aspirate material, and serology. The latter methods use crude antigen preparations lacking in specificity. A previously described cloned antigen, rK39, of Leishmania specific for all members of the L. donovani complex (L. chagasi, L. donovani, L. infantum) was very useful in the serodiagnosis by ELISA of both human and canine VL. The present study demonstrated that rK39 seroreactivity correlated with active disease. The sera from early or self-healing infected subjects reacted with leishmanial lysate and were generally nonreactive with rK39. These data demonstrate the utility of rK39 in the serodiagnosis of VL and as an indicator of active disease.

Antibodies to human immunodeficiency virus in human sera induce cell-mediated lysis of human immunodeficiency virus-infected cells

The capacity of human immunodeficiency virus (HIV) antibody-positive sera from homosexually active men without acquired immune deficiency syndrome to lyse the HIV-infected T cell lines MOLT-4f and CCRF-CEM (CEM) in cooperation with lymphocytes from normal donors was investigated. Twenty-seven HIV antibody-positive sera, most of which enhanced the killing of HIV-infected MOLT-4f and CEM target cells by normal mononuclear cells were studied in detail. HIV antibody-positive sera resulted in lysis at dilutions as high as 1/10,000. HIV antibody-negative sera did not augment lysis of infected target cells. In addition, lysis of uninfected targets was not enhanced in the presence of HIV antibody-positive sera. Because fractionation of the HIV antibody-positive sera on a protein A affinity column resulted in recovery of the activity from the IgG fraction, the extra cytotoxic activity mediated by nonimmune cells in the presence of immune sera appears to be antibody-dependent. Furthermore, the cytotoxic effector cells were in the nonrosetting fraction of lymphocytes and expressed Leu-11 (cluster designation (CD)15) antigens, which is characteristic of cells participating in antibody-dependent cellular cytotoxicity reactions. The antibody specificity of the sera, determined by radioimmunoprecipitation, provides evidence that antibody-dependent cellular cytotoxicity can occur even when there are no detectable antibodies directed against gag proteins. Sera which lacked detectable antibodies to the envelope protein gp120 by radioimmunoprecipitation did not mediate antibody-dependent cellular cytotoxicity.

Antibodies to human immunodeficiency virus in human sera induce cell-mediated lysis of human immunodeficiency virus-infected cells

The capacity of human immunodeficiency virus (HIV) antibody-positive sera from homosexually active men without acquired immune deficiency syndrome to lyse the HIV-infected T cell lines MOLT-4f and CCRF-CEM (CEM) in cooperation with lymphocytes from normal donors was investigated. Twenty-seven HIV antibody-positive sera, most of which enhanced the killing of HIV-infected MOLT-4f and CEM target cells by normal mononuclear cells were studied in detail. HIV antibody-positive sera resulted in lysis at dilutions as high as 1/10,000. HIV antibody-negative sera did not augment lysis of infected target cells. In addition, lysis of uninfected targets was not enhanced in the presence of HIV antibody-positive sera. Because fractionation of the HIV antibody-positive sera on a protein A affinity column resulted in recovery of the activity from the IgG fraction, the extra cytotoxic activity mediated by nonimmune cells in the presence of immune sera appears to be antibody-dependent. Furthermore, the cytotoxic effector cells were in the nonrosetting fraction of lymphocytes and expressed Leu-11 (cluster designation (CD)15) antigens, which is characteristic of cells participating in antibody-dependent cellular cytotoxicity reactions. The antibody specificity of the sera, determined by radioimmunoprecipitation, provides evidence that antibody-dependent cellular cytotoxicity can occur even when there are no detectable antibodies directed against gag proteins. Sera which lacked detectable antibodies to the envelope protein gp120 by radioimmunoprecipitation did not mediate antibody-dependent cellular cytotoxicity.

Phase-separation immunoassays

Solid-phase-based immunoassays have traditionally been plagued by nonspecific binding to the solid phase and by slow reaction kinetics relative to reactants that are free to diffuse in solution. We have developed two novel immunoassays in which the solid phase is generated in situ after the specific binding reaction has occurred, thereby enhancing reaction kinetics and minimizing the opportunities for non-specific binding. In the first system, the capture antibody is conjugated to an organic monomer, polymerization of which to form insoluble polymer particles is initiated by a reaction involving free radicals. The amount of signal-labeled antibody incorporated into the resulting particles is directly proportional to the concentration of antigen. The principle is illustrated for the simultaneous assay of IgG and IgM in a single sample. In the second system, capture antibody is conjugated to a polymer, the solubility of which is a function of temperature. Specific binding is conducted below the critical solution temperature of the polymer, which is then separated from solution by increasing the temperature above the critical temperature. The incorporation of signal-labeled antibody into the precipitated polymer is directly proportional to the concentration of antigen. This principle is illustrated for the assay of hepatitis B surface antigen and Chlamydia trachomatis.

Phase-separation immunoassays

Solid-phase-based immunoassays have traditionally been plagued by nonspecific binding to the solid phase and by slow reaction kinetics relative to reactants that are free to diffuse in solution. We have developed two novel immunoassays in which the solid phase is generated in situ after the specific binding reaction has occurred, thereby enhancing reaction kinetics and minimizing the opportunities for non-specific binding. In the first system, the capture antibody is conjugated to an organic monomer, polymerization of which to form insoluble polymer particles is initiated by a reaction involving free radicals. The amount of signal-labeled antibody incorporated into the resulting particles is directly proportional to the concentration of antigen. The principle is illustrated for the simultaneous assay of IgG and IgM in a single sample. In the second system, capture antibody is conjugated to a polymer, the solubility of which is a function of temperature. Specific binding is conducted below the critical solution temperature of the polymer, which is then separated from solution by increasing the temperature above the critical temperature. The incorporation of signal-labeled antibody into the precipitated polymer is directly proportional to the concentration of antigen. This principle is illustrated for the assay of hepatitis B surface antigen and Chlamydia trachomatis.

Occurrence of proteins immunoreactive with anti-coupling factor B in phosphorylating membrane preparations

Coupling factor B has been isolated from beef heart mitochondria, apparently in multiple forms which differ in molecular weight and specific activity. Since it has no known intrinsic catalytic activity, detection and quantitation have been based upon the factor B-dependent stimulation of ATP-linked activities in factor B-deficient sub-mitochondrial particles. This communication reports the development of a reliable and more universally applicable enzyme-linked immunosorbent assay (ELISA) for detection and quantitation of factor B in soluble or membranous preparations. The assay requires nanoliter volumes of rabbit antiserum raised against purified factor B and will detect nanogram amounts of the coupling factor. Analysis of beef heart submitochondrial particles using a competitive binding ELISA indicated a factor B content of 0.27 nmol/mg protein, making factor B stoichiometric with F1 (0.3--0.6 nmol/mg). Furthermore, application of the factor B ELISA has indicated the presence of material cross-reacting with the beef heart factor B-antiserum in phosphorylating membranes from chloroplasts, Escherichia coli, Paracoccus denitrificans and the thermophilic bacterium, PS3. Negative results were obtained with mitochondria and microsomes from rat liver, purple membranes from Halobium halobacterium and sarcoplasmic reticulum from rabbit skeletal muscle.

Coregulation of oxidized nicotinamide adenine dinucleotide (phosphate) transhydrogenase and glutamate dehydrogenase activities in enteric bacteria during nitrogen limitation

The relationship between oxidized nicotinamide adenine dinucleotide (phosphate) [NAD(P)+] transhydrogenase (EC 1.6.1.1) and NAD(P)+ glutamate dehydrogenase in several enteric bacteria which differ slightly in their regulation of nitrogen metabolism was studied. Escherichia coli strain K-12 was grown on glucose and various concentrations of NH4Cl as the sole nitrogen source. In the range of 0.5 to 20 mM NH4Cl, the energy-independent transhydrogenase increased two to threefold. Comparable changes occurred in NAD(P)+-linked glutamate dehydrogenase. NH4Cl concentrations of 20 to 60 mM resulted in relatively constant specific activities for both enzymes. Higher exogenous NH4Cl, however, led to a decline in both activities. Isocitrate dehydrogenase, another potential source of cellular NADPH, was insensitive to NH4Cl limitation. Similar studies in the presence of glutamate and different exogenous NH4Cl concentrations again showed concerted effects on both enzymes. Growth on glutamate as the sole nitrogen source led to severe repression of both transhydrogenase and glutamate dehydrogenase. In Salmonella typhimurium, both enzymes were unaffected by limiting NH4Cl or growth on glutamate as the sole nitrogen source. Both were, however, repressed by growth on aspartate, a potential source of cellular glutamate. Coordinate changes in glutamate dehydrogenase and transhydrogenase were also evident in Klebsiella aerogenes, particularly under conditions in which glutamate dehydrogenase was regulated inversely to glutamate synthetase. Coordinate changes in glutamate dehydrogenase and transhydrogenase in enteric bacteria are discussed in terms of the possible involvement of the latter enzyme as a direct source of NADPH in the ammonia assimilation system.

Energy-linked and energy-independent transhydrogenase activities in Escherichia coli vesicles

Active transport vesicles of Escherichia coli were shown to possess low levels of energy-independent and energy-dependent nicotinamide nucleotide transhydrogenase activities. Breakage of such vesicles in a French pressure cell resulted in a fraction which had an 8-10-fold increased respiration- and ATP-driven transhydrogenase activities. Stimulation of the ATPase activity in vesicles with Triton X-100 was also paralledled by a 2-fold increase in the energy-independent transhydrogenase. Disruption of the vesicles similarly resulted in increases in the energy-independent transhydrogenase, NADH and succinate oxidase activities but a decrease in succinate supported proline uptake. In the light of these findings, the "sidedness' of the vesicle membranes is discussed.

Studies on energy-linked reactions: isolation and properties of mitochondrial venturicidin-resistant mutants of Saccharomyces cerevisiae

Venturicidin is a specific inhibitor of aerobic growth of yeast and has no effect on fermentative growth, a result which is consistent with its known mode of action on mitochondrial oxidative phosphorylation. Venturicidin-resistant mutants of Saccharomyces cerevisiae have been isolated and form two general classes: class 1, nuclear mutants which are resistant to a variety of mitochondrial inhibitors and uncouplers, and class 2, mitochondrial mutants of phenotype VENR OLYR and VENR TETR in vivo. VENR OLYR mutants show a high degree of resistance to venturicidin and oligomycin at the whole cell and mitochondrial ATPase level but, in contrast, no resistance at the mitochondrial level is observed with VENR TETR mutants. Venturicidin resistance/sensitivity can be correlated with two binding sites on mitochondrial ATPase, one of which is common to the oligomycin binding site and the other is common to the triethyl tin binding site. Biochemical genetic studies indicate that two mitochondrial genes specify venturicidin resistance/sensitivity and that the mitochondrial gene products are components of the mitochondrial ATPase complex.

Membrane-lipid unsaturation and mitochondrial function in Saacharomyces cerevisiae

The lipid composition of yeast cells was manipulated by the use of an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae. There was a 2-3-fold decrease in the concentration of cytochromes a+a3 when the unsaturated fatty acid content of the cells was decreased from 60-70% of the total fatty acid to 20-30%. The amounts of cytochromes b and c were also decreased under these conditions, but to a lesser extent. Further lipid depletion, to proportions of less than 20% unsaturated fatty acid, led to a dramatic decrease in the content of all cytochromes, particularly cytochromes a+a3. The ATPase (adenosine triphosphatase), succinate oxidase and NADH oxidase activities of the isolated mitochondria also varied with the degree of unsaturation of the membrane lipids. The lower the percentage of unsaturated fatty acid, the lower was the enzymic activity. Inhibition of mitochondrial ATPase by oligomycin, on the other hand, was not markedly influenced by the membrane-lipid unsaturation. Npn-linear Arrenius plots of mitochondrial membrane-bound enzymes showed transition temperatures that were dependent on the degree of membrane-lipid unsaturation. The greater the degree of lipid unsaturation, the lower was the transition temperature. It was concluded that the degree of unsaturation of the membrane lipids plays an important role in determining the properties of mitochondrial membrane-bound enzymes.