Alpha-adrenoceptors and angiotensinogen gene expression in opossum kidney cells

To investigate whether alpha (alpha)-adrenoceptor agonists have a stimulatory effect on the expression of the angiotensinogen (Ang) gene in opossum kidney (OK) cells, we used OK 27 cells with a fusion gene containing the 5'-flanking regulatory sequence of the rat angiotensinogen gene fused with a human growth hormone (hGH) gene as a reporter, pOGH (Ang N-1498/+18), permanently integrated into their genomes. The level of expression of the pOGH (Ang N-1498/+18) was quantitated by the amount of immunoreactive-human growth hormone (IR-hGH) secreted into the medium. The addition of iodoclonidine (alpha 2-adrenoceptor agonist, 10(-13) to 10(-9) M) and phorbol 12-myristate 13-acetate (PMA, 10(-13) to 10(-5) M) stimulated the expression of pOGH (Ang N-1498/+18) in a dose-dependent manner, whereas the addition of phenylephrine (alpha 1-adrenoceptor agonist, 10(-13) to 10(-5) M) had no effect. The stimulatory effect of iodoclonidine was blocked by the presence of yohimbine (alpha 2-adrenoceptor antagonist) and staurosporine (an inhibitor of protein kinase C) but not blocked by the presence of prazosin (alpha 1-adrenoceptor antagonist) or Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A). The addition of iodoclonidine, phenylephrine or PMA had no effect on the expression of pTKGH in OK 13 cells, an OK cell line, into which had been stably integrated a fusion gene, pTKGH containing the promoter/enhancer DNA sequence of the viral thymidine-kinase (TK) gene fused with a human growth hormone gene as a reporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of estrogen on apoptotic pathways in human breast cancer cell line MCF-7

We utilized a reverse transcription-PCR method to examine the effect of estrogen on the expression of mRNA for Bcl-2 and Bax, two modulatory proteins in the apoptotic pathway, in human breast cancer cell line MCF-7. We found that the bcl-2 mRNA levels in the cells exposed to 17 beta-estradiol were higher than those of control cells. Although the relative bax mRNA levels remained unchanged, the changes in bcl-2 mRNA level occurred in a time- and concentration-dependent fashion. In addition, pretreatment with 17 beta-estradiol protected MCF-7 cells from apoptosis. Our study provides evidence that responses of breast epithelial cells toward a steroid sex hormone involve regulation of the apoptotic pathway.

Investigation of the active site cysteine residue of rat liver mitochondrial aldehyde dehydrogenase by site-directed mutagenesis

To determine the active site cysteine residue in aldehyde dehydrogenase, we mutated amino acid residues 49, 162, and 302 of recombinantly expressed rat liver mitochondrial (class 2) aldehyde dehydrogenase. The C49A and C162A mutants were fully active tetrameric enzymes, although the C162A mutant was found to be highly unstable. The C302A mutant was also a tetramer and bound coenzyme, but lacked both dehydrogenase and esterase activities. To test for the role of cysteine 302 as a nucleophile, the residue was mutated to a serine, a poor nucleophile. this C302S mutant was active but was a much poorer catalyst, with a kcat/Km value 7 x 10(5) times lower than that of the recombinant native enzyme. Unlike with native enzyme where deacylation is rate limiting, formation of the serine hemiacetal intermediate appeared to be the rate-limiting step. Cysteine 302 is the only strictly conserved cysteine residue among all the available sequences of the aldehyde dehydrogenase superfamily, supporting the role of this residue as the active site nucleophile of aldehyde dehydrogenase.

Expression of the angiotensinogen gene is synergistically stimulated by 8-BrcAMP and Dex in opossum kidney cells

We transiently transfected fusion genes with the 5'-flanking region of the angiotensinogen gene linked to a bacterial chloramphenicol acetyltransferase (CAT) coding sequence as a reporter into opossum kidney (OK) cells. The addition of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) (10(-3)-10(-7) M) or forskolin (10(-9)-10(-5) M) stimulated the expression of the plasmid pOCAT [angiotensinogen nucleotide (N) -1498/+18] fusion gene in OK cells in a dose-dependent manner. The addition of dexamethasone (Dex) (10(-6) M) further enhanced the stimulatory effect of 8-BrcAMP or forskolin, whereas the addition of (R)-p-adenosine 3',5'-cyclic monophosphorothioate [(Rp)-cAMP[S], an inhibitor of cAMP-dependent protein kinase A, I and II] blocked the stimulatory effect of 8-BrcAMP. Furthermore, the addition of 8-BrcAMP (10(-3) M) or Dex (10(-6) M) or a combination of both stimulated the expression of pOCAT (angiotensinogen N -1138/+18), pOCAT (angiotensinogen N -960/+18), pOCAT (angiotensinogen N -814/+18), and pOCAT (angiotensinogen N -688/+18), but had no effect on the expression of pOCAT (angiotensinogen N -280/+18), pOCAT (angiotensinogen N -198/+18), pOCAT (angiotensinogen N -110/+18), pOCAT (angiotensinogen N -53/+18), and pOCAT (angiotensinogen N -35/+18). To further localize the putative cAMP-responsive element (CRE) in the angiotensinogen gene, we constructed fusion genes by inserting the DNA fragments angiotensinogen N -814 to N -689, angiotensinogen N -814 to N -761, and angiotensinogen N -760 to N -689 of the 5'-flanking region of the angiotensinogen gene upstream of the thymidine kinase (TK) promoter fused to a CAT gene and introduced them into OK cells.(ABSTRACT TRUNCATED AT 250 WORDS)

[Lipid metabolism and pregnancy induced hypertension]

Lipid metabolism was studied in 30 healthy non-pregnant women, 35 normal pregnant women and 34 patients with pregnancy induced hypertension (PIH). Total cholesterol (TC), triglycerides (TG), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), LDL-C/HDL-C ratio, and athero-sclerosis index (AI) were determined. In comparison with the non-pregnant status, lipid levels did not increased during normal mid-trimester pregnancy, but significantly increased at late trimester of normal pregnancy (P < 0.05). There was no significant difference in lipid levels between normal late pregnancy and PIH of mild and moderate degree, but TG and AI were significantly higher in cases with severe PIH. It showed that: lipid profiles in severe PIH was characterized by type IV hyperlipidemia; high lipid levels during normal late pregnancy might be a physiological phenomenon which presents a risk factor for PIH; marked increase of TG and AI in severe PIH may result in a rise of lipid peroxide (LPO).

Isoproterenol and 8-bromo-cyclic adenosine monophosphate stimulate the expression of the angiotensinogen gene in opossum kidney cells

To investigate whether the expression of the renal angiotensinogen (ANG) gene is regulated by beta-adrenoceptors and the cAMP-dependent protein kinase A pathway, we introduced stably the fusion gene containing the 5'-flanking regulatory sequence of the ANG gene with a human growth hormone (hGH) gene as a reporter, pOGH (ANG N-1498/+18), into opossum kidney (OK) cells. We successfully obtained several stable transformants with a high expression of the pOGH (ANG N-1498/+18) fusion gene. One stable transformant (OK 27) that is able to maintain the expression of pOGH (ANG N-1498/+18) in culture for more than a year was used in the present study. The level of expression of the pOGH (ANG N-1498/+18) in OK 27 was evaluated by the amount of immunoreactive-hGH (IR-hGH) secreted into the culture medium. The addition of isoproterenol (10(-11) M to 10(-9) M) stimulated the expression of pOGH (ANG N-1498/+18) and increased the accumulation of intracellular cAMP. Higher concentrations of isoproterenol (that is, greater than 10(-9) M) had low or minimal effect. In contrast, the addition of 8-bromo-cAMP (8-Br-cAMP) and forskolin stimulated the expression of pOGH (ANG N-1498/+18) in a dose-dependent manner. The stimulatory effect of isoproterenol was blocked by the presence of propranolol, atenolol and ICI 118,551. The addition of ICI 118,551, however, was less effective than atenolol. Furthermore, the stimulatory effect of isoproterenol and 8-Br-cAMP on the expression of the pOGH (ANG N-1498/+18) was inhibited by the presence of Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A I and II).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of changing glutamate 487 to lysine in rat and human liver mitochondrial aldehyde dehydrogenase. A model to study human (Oriental type) class 2 aldehyde dehydrogenase

Many Oriental people possess a liver mitochondrial aldehyde dehydrogenase where glutamate at position 487 has been replaced by a lysine, and they have very low levels of mitochondrial aldehyde dehydrogenase activity. To investigate the cause of the lack of activity of this aldehyde dehydrogenase, we mutated residue 487 of rat and human liver mitochondrial aldehyde dehydrogenase to a lysine and expressed the mutant and native enzyme forms in Escherichia coli. Both rat and human recombinant aldehyde dehydrogenases showed the same molecular and kinetic properties as the enzyme isolated from liver mitochondria. The E487K mutants were found to be active but possessed altered kinetic properties when compared to the glutamate enzyme. The Km for NAD+ at pH 7.4 increased more than 150-fold, whereas kcat decreased 2-10-fold with respect to the recombinant native enzymes. Detailed steady-state kinetic analysis showed that the binding of NAD+ to the mutant enzyme was impaired, and it could be calculated that this resulted in a decreased nucleophilicity of the active site cysteine residue. The rate-limiting step for the rat E487K mutant was also different from that of the recombinant rat liver aldehyde dehydrogenase in that no pre-steady-state burst of NADH formation was found with the mutant enzyme. Both the rat native enzyme and the E487K mutant oxidized chloroacetaldehyde twice as fast as acetaldehyde, indicating that the rate-limiting step was not hydride transfer or coenzyme dissociation but depended upon nucleophilic attack. Each enzyme form showed a 2-fold activation upon the addition of Mg2+ ions. Substituting a glutamine for the glutamate did not grossly affect the properties of the enzyme. Glutamate 487 may interact directly with the positive nicotinamide ring of NAD+ for the Ki of NADH was the same in the lysine enzyme as it was in the glutamate form. Because of the altered NAD+ binding properties and kcat of the E487K variant, it is assumed that people possessing this form will not have a functional mitochondrial aldehyde dehydrogenase.

Stimulation of pS2 expression by diet-derived compounds

Epidemiological studies suggest a lowered risk of hormone-dependent cancers among vegetarians, but the basis for this association remains unclear. Vegetables and fruits contain certain compounds which can be converted to biologically active hormone-like substances, such as lignans and isoflavones, by intestinal flora. The interaction of these compounds with endogenous hormones may be a novel, diet-dependent mechanism in cancer prevention. To explore this possibility, we developed a rapid, specific assay system to screen for compounds with estrogen-like activity in tissue culture. We utilized the estrogen receptor-positive breast cancer cell MCF-7 and monitored the expression of the estrogen-responsive protein pS2 by Northern blots. Our results indicated that the phenolic compounds daidzein, equol, nordihydroguaiaretic acid, enterolactone, and kaempferol were able to elicit an estrogen-like response, while quercetin and enterodiol were not.

[Complication of ascites in pregnancy-induced hypertension]

Twenty three pregnancy-induced hypertension (PIH) patients with ascites were treated in Beijing Obstetrics and Gynecology Hospital from Jan. 1981 to April 1992. The incidence of ascites in PIH was 1.9/1000 in total in this study, and 21.6/1000 in severe PIH. Clinical manifestations showed an early onset of PIH at 29.4 +/- 4.8 weeks, and ascites occurred at 32.4 +/- 7.4 weeks. There were 18 cases out of 23 who had no routine antenatal care, all of them had complications with IUGR. Laboratory studies: ascites showed transudate in all of them except one with chronic nephritis exhibiting milky appearance. 10% of patients had abnormal complete blood count (CBC) and 13%-17% abnormal electrolytes. 17.0% of the patients had GPT > 30IU, 21.0% urea nitrogen > 35 g/L, 95.7% had plasma albumin < 35 g/L. The ratio of A/G was < 1.5 in all patients. We conclude that once PIH was 1.5 in all patients. We conclude that once PIH was complicated by ascites, it can not be cured by active treatment. It is an indication for termination of pregnancy. After delivery the ascites and pleural effusion gradually disappeared in 2 weeks. Perinatal mortality rate was as high as 42.1% because of premature induced labor and IUGR.

Production of human plasma retinol-binding protein in Escherichia coli

We designed a polymerase chain reaction (PCR) primer pair which allowed us to clone the cDNA coding for the human plasma retinol-binding protein (hRBP) into an Escherichia coli expression vector. Production of hRBP was confirmed by probing Western blots with antisera against plasma hRBP. Purification and characterization of the E. coli-produced plasma hRBP are also described. The availability of this expression system makes it possible to obtain large quantities of hRBP to facilitate our continuing studies of retinol and RBP metabolism.

Cloning and expression of the full-length cDNAS encoding human liver class 1 and class 2 aldehyde dehydrogenase

The amino acid sequences of both human class 1 and 2 aldehyde dehydrogenase (ALDH) and the sequences of the genes coding for them are known. Based on this sequence data, we designed primers and isolated the full-length cDNAs encoding both isozymes from a human liver mRNA pool. cDNAs were subcloned in the plasmid pT7-7 and expressed in Escherichia coli with a yield of approximately 3 mg ALDH protein/liter of cell culture, although only one-third of the enzyme was soluble. The soluble recombinantly expressed ALDHs were purified to homogeneity using a hydroxyacetophenone-Sepharose affinity column. The mitochondrial isozyme had a subunit molecular weight of 55 kDa, an isoelectric point of 4.9, and a specific activity of 1.10 units/mg, which were in good agreement with that from the native enzyme. The expressed cytosolic isozyme had the same subunit molecular weight (55 kDa) and pI (5.4) as that reported for the native enzyme and had a specific activity of 0.26 units/mg. The expressed mitochondrial isozyme could be recognized by antibodies raised against rat mitochondrial ALDH, whereas the cytosolic isozyme could be recognized by antibody raised against horse cytosolic ALDH.

The nucleotide sequence of Schwanniomyces occidentalis alpha-amylase gene

The nucleotide sequence of the coding and regulatory regions of the alpha-amylase-encoding gene (AMY) of Schwanniomyces occidentalis has been determined. This sequence contained an open reading frame of 512 codons, from which a protein with Mr of 53,723 could be predicted. A putative signal sequence encoding for 25 amino acids was proposed for the 5' end of the open reading frame. Regulatory sequences, such as TATA box, CCAAT box and a signal sequence for polyadenylation and transcription termination could be found in the flanking regions of AMY gene. The deduced amino acid sequence also contained four common conserved regions characteristic of other alpha-amylase proteins.

Effects of protein size on the rate of import of the precursors of aldehyde dehydrogenase and ornithine transcarbamylase into rat liver mitochondria

It is known that a signal peptide is required for the import of a protein into mitochondrial matrix. It is also known that a signal peptide can be attached to any protein and allow it to be imported. We recently reported that the rate of import of rat liver mitochondrial aldehyde dehydrogenase precursor was slower than that of ornithine transcarbamylase precursor (Wang TTY, Farrés J, and Weiner H. Arch Biochem Biophys 272, 440-449, 1989). It was not known if the difference in the rate of import was related to the fact that the mature portion of aldehyde dehydrogenase is larger (500 amino acids compared with 322 amino acids) or because the signal peptides were different. We further showed that treatment of the mitochondria with alcohols caused an inhibition of the import of the precursor of aldehyde dehydrogenase but not that of ornithine transcarbamylase. In the present study we constructed chimeric proteins that contained the signal peptide from one precursor protein and the mature portion from the other. We found that the rate of import was related to the overall size of the precursor protein. Consistent with this observation was finding that a truncated aldehyde dehydrogenase precursor, which contained 317 amino acids, was imported more rapidly than was the authentic precursor. Consistent with this finding was the fact that butanol caused the inhibition of only the large precursor proteins. Thus, it appears that size of the protein being imported is a major determinant of the rate at which a precursor protein is imported into mitochondria.

Cell-cell interactions trigger the rapid induction of a specific high mobility group-like protein during early stages of conjugation in Tetrahymena

Conjugation in Tetrahymena represents an ordered developmental pathway which represents the sexual phase of the ciliate life cycle. This pathway is initiated when starved cells of opposite mating types are mixed and are allowed to make a series of cell-cell contacts (a period termed costimulation) which lead to the formation of mating pairs. Here, we demonstrate that two previously described abundant high mobility group (HMG)-like proteins, HMG B and HMG C, whose synthesis appeared to be coordinately regulated in vegetative cells, are not required during the same stages of conjugation. The level of mRNA for both HMG B and HMG C is high during vegetative growth and during the development of new macronuclei. However, specific induction of HMG B mRNA is observed soon after cells of opposite mating types are mixed. Thus, the genes which encode HMG B and HMG C in Tetrahymena can be controlled independently or coordinately. Nuclear run-on experiments show that a significant factor underlying the rapid induction of HMG B message early in the sexual cycle is an increase in the transcriptional activity of the HMG B gene. Experiments are presented which show that this induction of HMG B message requires protein synthesis and is dependent upon the cell-cell contacts made during costimulation. Essentially all of the HMG B protein, which is newly synthesized during this period, is targeted to parental macronuclei where it serves an as yet undetermined function(s).

Effects of alcohol on the import of aldehyde dehydrogenase precursor into rat liver mitochondria

We previously showed that incubation of rat liver mitochondria with alcohols resulted in the inhibition of the import of aldehyde dehydrogenase precursor but not that of ornithine transcarbamylase precursor (Wang TTY, Farrés J, and Weiner H: Arch Biochem Biophys 272:440-449, 1989). The time required for inhibition of import to occur was now measured with ethanol (200 mM) and butanol (100 mM) at 0 degree and 30 degrees C. It required approximately 30 min to achieve 50% inhibition with butanol and 50 min with ethanol. To further substantiate the membrane perturbing effects of alcohols, we also examined the effect of oleic acid on import. We found that incubation of mitochondria with oleic acid (0-100 microM) resulted in inhibition of aldehyde dehydrogenase precursor import in a dose response fashion. In addition to in vitro effects of alcohols on import, we conducted a preliminary study on import of protein into liver mitochondria isolated from rats fed ethanol. We found that the rate of aldehyde dehydrogenase precursor import into liver mitochondria isolated from ethanol fed rats was identical to that from control. The results are consistent with finding that the activity and amount of aldehyde dehydrogenase was the same in mitochondria isolated from the alcohol-fed or control animals.

Cloning and Expression of a Schwanniomyces occidentalis α-Amylase Gene in Saccharomyces cerevisiae

An α-amylase gene ( AMY ) was cloned from Schwanniomyces occidentalis CCRC 21164 into Saccharomyces cerevisiae AH22 by inserting Sau 3AI-generated DNA fragments into the Bam HI site of YEp16. The 5-kilobase insert was shown to direct the synthesis of α-amylase. After subclones containing various lengths of restricted fragments were screened, a 3.4-kilobase fragment of the donor strain DNA was found to be sufficient for α-amylase synthesis. The concentration of α-amylase in culture broth produced by the S. cerevisiae transformants was about 1.5 times higher than that of the gene donor strain. The secreted α-amylase was shown to be indistinguishable from that of Schwanniomyces occidentalis on the basis of molecular weight and enzyme properties.

Uterine malignancy developing after long term use of IUCD additional report of 2 cases: endometrial stromal sarcoma and leiomyosarcoma

In our 2 previous papers published in this Journal, we had 5 cases of uterine malignancies developing after long term use of IUCD's. In the present paper 2 cases of such association are to be added. One case ATH with right adnexectomy was performed for persisting vaginal bleeding after 22 years of Lippes Loop application and recurrence 8 years after the first operation. Pathological diagnosis is endometrial stromal sarcoma. The other case is a leiomyosarcoma developing after 25 years of Lippes Loop application. Although no cause and effect relationship between IUCD use and uterine malignancy in human beings has been proved, the increase in such cases suggests to us that long term application should be avoided, particularly in view of the positive animal experiments. The successive detection of such cases in a relatively short period of time prompts us to make further studies to gain a deeper insight into such associations.

Liver mitochondrial aldehyde dehydrogenase: in vitro expression, in vitro import, and effect of alcohols on import

An in vitro expression plasmid (pGRAP) that contained the cDNA coding for the rat mitochondrial aldehyde dehydrogenase precursor was constructed, mRNA was synthesized then translated, and the in vitro synthesized precursor of aldehyde dehydrogenase was used in an in vitro import assay. As expected the 19 amino acid signal peptide of the precursor allowed import of the precursor into rat liver mitochondria. This in vitro system was used to examine the effect of alcohols on import. It was found that the alcohols (ethyl, butyl, hexyl, and octyl) tested inhibited the import of the aldehyde dehydrogenase precursor. Pretreatment of the mitochondria with alcohol was responsible for the inhibition. The inhibition appeared to be relatively specific for pre-aldehyde dehydrogenase as the precursor of ornithine transcarbamylase was still imported in the presence of alcohols. Of potential physiological significance was finding that ethanol inhibited import in a dose-response fashion; 50% inhibition occurred at 75 mM, a concentration achievable during the ingestion of alcohol. In addition, the concentrations of alcohols required to produce an inhibitory effect on import decreased as the hydrocarbon chain length of alcohols increased. The inhibitory effect of alcohols appeared to be specific as other solvents examined did not inhibit import. We postulate that alcohols may perturb the mitochondrial membrane and affect the receptor-translocator necessary for the import of the aldehyde dehydrogenase precursor.

The physiological role of lipoxygenase in ethylene formation from 1-aminocyclopropane-1-carboxylic acid in oat leaves

In order to understand the physiological significance of the in-vitro lipoxygenase (EC 1.13.11.12)-mediated ethylene-forming system (J.F. Bousquet and K.V. Thimann 1984, Proc. Natl. Acad. Sci. USA 81, 1724-1727), its characteristics were compared to those of an in-vivo ethylene-forming system. While oat (Avena sativa L.) leaves, as other plant tissues, preferentially converted only one of the 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC) isomers to 1-butene, the lipoxygenase system converted all four AEC isomers to 1-butene with nearly equal efficiencies. While the in-vivo ethylene-forming system of oat leaves was saturable with ACC with a Km of 16 μM, the lipoxygenase system was not saturated with ACC even at 10 mM. In contrast to the in-vivo results, only 10% of the ACC consumed in the lipoxygenase system was converted to ethylene, indicating that the reaction is not specific for ethylene formation. Increased ACC-dependent ethylene production in oat leaves following pretreatment with linoleic acid has been inferred as evidence of the involvement of lipoxygenase in ethylene production. We found that pretreating oat leaves with linoleic acid resulted in increased ACC uptake and thereby increased ethylene production. A similar effect was observed with oleic acid, which is not a substrate of lipoxygenase. Since linoleic acid hydroperoxide can substitute for lipoxygenase and linoleic acid in this system, it is assumed that the alkoxy radicals generated during the decomposion of linoleic acid hydroperoxide are responsible for the degradation of ACC to ethylene. Our results collectively indicate that the reported lipoxygenase system is not the in-vivo ethylene-forming enzyme.

Intracellular pteroylpolyglutamate hydrolase from human jejunal mucosa. Isolation and characterization

Human jejunal intracellular pteroylpolyglutamate hydrolase was purified 30-fold from intestinal mucosa. The apparent molecular weight of the enzyme was 75,000 by Sephadex G-200 gel filtration, and the isoelectric point was at pH 8.0. The enzyme was maximally active at pH 4.5 and was unstable at increasing temperatures. Intracellular pteroylpolyglutamate hydrolase cleaved both terminal and internal gamma-glutamate linkages. In contrast, brush-border pteroylpolyglutamate hydrolase catalyzed the hydrolysis of only terminal gamma-glutamate linkages. The intracellular enzyme showed greatest affinity for the complete folic acid molecule with longer glutamate chains. Subcellular fractionation studies showed the intracellular enzyme was localized in lysosomes. These data show that the properties of human jejunal intracellular pteroylpolyglutamate hydrolase are distinct from those of the brush-border enzyme but are similar to the properties of intracellular pteroylpolyglutamate hydrolase described in other tissues.

Pattern recognition analysis of in vivo enzyme-substrate fluorescence velocities in microorganism detection and identification

A spectrometric technique is presented that combines most of the important criteria necessary for efficient detection and identification of microorganisms. These criteria include simplicity of experimental design, various degrees of sensitivity and selectivity, convenience, and total reaction times of less than 15 min. The study takes advantage of the inherent extracellular enzymes present in living as opposed to dead, non-enzyme-producing organisms. Sequentially these are harnessed in in vivo reactions with a substrate containing a select organic functional group that is known to be cleaved or hydrolyzed by a certain enzyme. The substrate is tailored so that one of the products can be induced to fluoresce, and by using a conventional spectrofluorimeter the rate at which the fluorescence appears can be recorded. By subjecting the same bacterial sample to a number of different enzyme substrates, a pattern of fluorescence response rates emerges from a 7 by 7 microorganism-substrate matrix. Detection limits ranged from 3.6 X 10(2) to 3.5 X 10(8) cells per ml for the Bacillus globigii-indoxyl acetate and Escherichia coli-diacetylfluorescein pairs, respectively. The specificity and versatility of the method for bacterial determination is demonstrated in probing different bacterial enzymes through their spectrally active metabolic products.

Pteroylpolyglutamate hydrolase from human jejunal brush borders. Purification and characterization

Pteroylpolyglutamate hydrolase was solubilized with Triton X-100 from human jejunal mucosal brush borders and purified approximately 5,000-fold using organomercurial affinity chromatography, DEAE-cellulose chromatography, and gel filtration. The apparent molecular weight of the purified enzyme in the Triton micelle was estimated as 700,000 using Bio-Gel A-1.5m gel filtration. Sodium dodecyl sulfate/urea-polyacrylamide gel electrophoresis followed by Coomassie stain demonstrated two polypeptide bands at 145,000 and 115,000 daltons. The purified enzyme had an isoelectric point of 7.2, was maximally active at pH 5.5, and was stable above pH 6.5 and at temperatures up to 65 degrees C for at least 90 min. Human jejunal brush-border pteroylpolyglutamate hydrolase is an exopeptidase which liberated [14C]Glu as the sole labeled product of PteGlu2[14C]Glue (where PteGlun represents pteroylpolyglutamate), failed to liberate a radioactive product from PteGlu2[14C]GluLeu2, and released all possible labeled PteGlun products during incubation with Pte[14C]GluGlu6 with the accumulation of Pte[14C]Glu. PteGlu2, PteGlu3, and PteGlu7 were substrates, each with Km = 0.6 microM, whereas PteGlu was a weak inhibitor of the hydrolysis of PteGlu3 with Ki = 20 microM. Components of the pteroyl moiety, Glu, and short chain Glun in alpha or gamma linkages were not inhibitory. The enzyme was activated by Zn2+ or Co2+. The properties of brush-border pteroylpolyglutamate hydrolase are different from those described for the soluble intracellular pteroylpolyglutamate hydrolase in other species and in human mucosa, yet are consistent with previous data on the process of hydrolysis of PteGlun in the intact human intestine.

Comparison of folate conjugase activities in human, pig, rat and monkey intestine

Folate conjugase, an intestinal enzyme that hydrolyzes dietary polyglutamyl folate to the absorbable monoglutamyl derivative, is present in two locations in human jejunal mucosa: one on the brush border membrane, the other soluble and intracellar. Although the brush border enzyme has not been found in the rodent, a recent study demonstrated both brush border and intracellular folate conjugases in the pig with properties similar to the human enzymes. To confirm and expand these data, we compared folate conjugase activities in intestinal brush border and 30,000 X g supernatant fractions in human, pig, rat and monkey mucosa. In both the human and pig, brush border folate conjugase was active from pH 4.5 to 8.5, and activity was significantly increased by zinc acetate. In contrast, folate conjugase activity was negligible in rat and monkey mucosal brush borders. Intracellular folate conjugase was maximally active at pH 4.5 in the human, pig and monkey, whereas this enzyme was equally active from pH 4.0 to 7.5 in the rat. In each species, supernatant activity at pH 4.5 was completely inhibited by p-hydroxymercuribenzoate. Although folate conjugase was quantitatively more active in the human than in the pig intestine, the brush border and intracellular enzymes exhibited similar properties. Sucrase, lactase and aminopeptidase activities were also similar in the two species. Our data show marked species differences in mucosal folate conjugase activities and indicate that the pig may be a suitable experimental animal for further studies of folate hydrolysis and absorption in humans.

Volatile N-nitrosamines in the urine of normal donors and of bladder cancer patients

Volatile N-nitrosamines were detected in the urine of male volunteers with gas-liquid and high-pressure liquid chromatography interfaced to the thermal energy analyzer. Of 50 samples from normal males, 10 contained nitrosodimethylamine (0.02 to 0.10 micrograms/liter), 6 contained nitrosodiethylamine (0.02 to 3.10), 9 contained nitrosomorpholine (0.006 to 0.67), and none contained nitrosodibutylamine. Of 4 samples from bladder cancer patients, 2 contained nitrosodibutylamine (0.35 and 0.66). Cigarette smoking did not appear to be related to the pattern or amount of urinary volatile N-nitrosamines. The possibility that the N-nitrosamines arise from the diet or from endogenous production is considered.

Modification of aspartic acid residues to induce trypsin cleavage

1,2-Diaminoethane and diaminomethane were coupled to aspartic acid residues in small peptides by means of a water-soluble carbodiimide. The resulting modified side chains sufficiently resembled lysine for trypsin to cleave the peptides. Similar modification of glutamic acid residues in peptides gave little or no susceptibility to trypsin.

Acyl and amino intermediates in penicillopepsin-catalysed reactions and activation by nonsubstrate peptides

The action of penicillopepsin on a variety of small peptides was studied qualitatively and kinetically. With the substrate benzyloxycarbonyl-Phe-Leu, benzyloxycarbonyl-Tyr-Leu and acetyl-Phe-Tyr the formation of Leu-Leu from the first two and Tyr-Tyr from the third substrate was observed. These reactions presumably proceed via a covalent amino-intermediate in analogy to pig pepsin. However, with penicillopepsin the yields of transpeptidation are low. In contrast, transpeptidations via acyl transfer proceed in high yield with a variety of substrates. With Leu-Trp-Met both acyl and amino transfer occurs as shown by the formation of Leu-Leu and Met-Met; unlike with pig pepsin, however, no Leu-Leu-Leu or Met-Met-Met was observed. Nonsubstrate peptides activate the cleavage of small substrates. (The term 'cleavage' is used here to imply that the reaction is either a hydrolysis or a transpeptidation, or both. The term 'hydrolysis' will only be used for strictly hydrolytic reactions.) As with pig pepsin the activators increase predominantly the transpeptidation reaction and have only small effects on hydrolysis. The activators increase kcat but have no effect on Km. Studies of the cleavage of six different peptides show that at pH 4.7 Km is lower than at pH 3.4 while kcat is unaffected. As with pig pepsin activation by nonsubstrate peptides is greater at pH 4.7 than at pH 3.4. Benzyloxycarbonyl-Glu-Tyr which is an inhibitor of trypsinogen activation (Ki = 50 μM) is an activator for the cleavage of Leu-Tyr-NH2 (Ka = 500 μM). Pepstatin, an inhibitor of the proteolytic activity of acid proteases, also inhibits the action of penicillopepsin on Leu-Tyr-NH2.The major conclusion from these studies is that the action of penicillopepsin on small peptides is qualitatively similar to that of pig pepsin. Transpeptidation reactions of both the amino acid and the acyl transfer type have been observed. However, there are considerable differences in the effects of pH, and in relative specificity between the two enzymes.

Effects of secondary binding by activator and inhibitor peptides on covalent intermediates of pig pepsin

A number of peptides were found to increase the activity of pig pepsin towards small synthetic substrates. The activators increase transpeptidation of both the acyl-transfer and the amino-transfer types by as much as 45-fold. The effect on hydrolysis varies from inhibition to modest activation, but is always less than the effect on transpeptidation. The kinetics of substrate cleavage are the converse of non-competitive inhibition and show an increase in kcat. and no effect on Km values. Lineweaver-Burk plots of results obtained in the presence of the activators indicate a substrate activation at high substrate concentration. This appears to be a co-operative effect, since it is not observed in the absence of the activators. The activation is greatest at pH 4.7, less at pH 3.4, and at pH 2.0 is observable only with some of the activator peptides. The results show directly the effect of secondary binding on the catalytic efficiency of pepsin. The most effective activators are those that are most hydrophobic. The results suggest that binding in the secondary binding sites causes an increase in hydrophobicity in the catalytic site which results in increased stability of the acyl and amino intermediates, and preferential reaction with acceptors other than water. The implication that the present results strengthen the case for a role of covalent intermediates in the hydrolysis of good substrates (high kcat. values) is discussed.

Acyl and amino intermediates in reactions catalysed by pig pepsin. Analysis of transpeptidation products

The action of pig pepsin on a variety of small peptides including Leu-Trp-Met-Arg, Leu-Trp-Met, Leu-Leu-NH2, benzyloxycarbonyl-Phe-Leu and Gly-Leu-Tyr was studied. Leu-Leu-Leu was found to be the major product from the substrates Leu-Trp-Met-Arg and Leu-Trp-Met, indicating that the predominant reaction at pH 3.4 was a transpeptidation of the acyl-transfer type. Leu-Leu-Leu was also formed in high yield by amino transfer from benzyloxycarbonyl-Phe-Leu. Like the amino-transfer reactions the acyl transfer proceeded via a covalent intermediate, since [14C]leucine was not incorporated into transpeptidation products and did not exchange with enzyme-bound leucine in the presence of acceptors. With Leu-Trp-Met both acyl and amino transpeptidation products, namely Leu-Leu, Leu-Leu-Leu, Met-Met and Met-Met-Met, were formed in addition to methionine and leucine. With Leu-Trp-Met-Arg (1 mM) the pH optimum for the rates of hydrolysis and acyl transfer is about pH 3.4. At this pH the rate of acyl transfer exceeds that of hydrolysis; at pH 2, however, hydrolysis was faster than transfer. A comparison of the effect of the length of substrates and products on the reaction rates allows the conclusion that the binding site can extend over eight to nine amino acid residues. Although the experiments provide no conclusive evidence for or against the involvement of amino and/or acyl intermediates in the hydrolysis of long peptides and proteins, the high yield of transpeptidation reactions of both types observed with some substrates suggests a major role for the intermediates in pepsin-catalysed reactions. The results also show that when pig pepsin is used for the digestion of proteins for sequence work, the likelihood of the formation of transpeptidation products is considerable. In this way peptides not present in the original sequence could easily form in a reasonably good yield.