The Escherichia coli polB locus is identical to dinA, the structural gene for DNA polymerase II. Characterization of Pol II purified from a polB mutant

Escherichia coli DNA polymerase II (Pol II) is a member of the group B, "alpha-like" family of DNA polymerases. Pol II is encoded by the damage-inducible dinA gene and exhibits SOS induction under the control of Lex A repressor. The polB gene was originally designated as the structural gene for Pol II based on the absence of detectable Pol II activity in cell lysates prepared from a strain containing the mutant polB100 allele. Because polB and dinA mapped at different chromosomal locations, it remained an open question whether polB, in addition to lexA, might be involved in regulating the expression of Pol II. We have cloned and sequenced the polB100 mutant allele, including adjacent surrounding sequences, and have expressed the mutant dinA gene from Pol B100 on a high copy number plasmid. Our sequence data reveal that polB and dinA represent the same gene and that the original transduction mapping of polB was inaccurate. We purified the mutant Pol B100 polymerase and show that it retains 5 to 10% of the wild-type level of polymerase activity. The Pol B100 mutation, Gly401 --> Asp401, is not located within any of the five conserved domains that define group B polymerases. Pol B100 retains a wild-type level of 3' --> 5' exonuclease activity. We suggest that the normal level of exonucleolytic proofreading associated with the mutant Pol B100 enzyme may explain the repeated failures, over the past two decades, to detect phenotypes in polB mutant strains.

Escherichia coli DNA polymerase II catalyzes chromosomal and episomal DNA synthesis in vivo

We have investigated a role for Escherichia coli DNA polymerase II (Pol II) in copying chromosomal and episomal DNA in dividing cells in vivo. Forward mutation frequencies and rates were measured at two chromosomal loci, rpoB and gyrA, and base substitution and frameshift mutation frequencies were measured on an F'(lacZ) episome. To amplify any differences in polymerase error rates, methyl-directed mismatch repair was inactivated. When wild-type Pol II (polB+) was replaced on the chromosome by a proofreading-defective Pol II exo- (polBex1), there was a significant increase in mutation frequencies to rifampicin resistance (RifR) (rpoB) and nalidixic acid resistance (NalR) (gyrA). This increased mutagenesis occurred in the presence of an antimutator allele of E. coli DNA polymerase III (Pol III) (dnaE915), but not in the presence of wild-type Pol III (dnaE+), suggesting that Pol II can compete effectively with DnaE915 but not with DnaE+. Sequencing the RifR mutants revealed a G --> A hot spot highly specific to Pol II exo-. Pol II exo- caused a significant increase in the frequency of base substitution and frameshift mutations on F' episomes, even in dnaE+ cells, suggesting that Pol II is able to compete with Pol III for DNA synthesis on F episomes.

Transmission factors of schistosomiasis japonica in the mountainous regions with type of plateau canyon and plateau basin

OBJECTIVE

To provide the scientific basis for formulating the control strategies of schistosomiasis japonica in mountainous regions in China Schistosomiasis Control Programme.

METHODS

We selected Chuanxing Village in Sichuan Province and Zhonghe Village in Yunnan Province as the two pilot areas for an epidemiological investigation according to their geographical and topographical characteristics, i.e. plateau canyon and plateau basin, respectively. Concentrated-egg hatching method in nylon tissue bag and Kato-Katz technique were used for the survey on prevalence rate and intensity of infection of man and domestic animals. Questionnaires were applied to investigating the infection sources, community behavior and the socioeconomic status. Snail survey and detection of cercaria-infested water bodies were conducted using routine techniques.

RESULTS

The results showed that in the endemic areas with plateau canyon, the key infection source was cattle. The infection rate in women was higher than that in men. The pattern of water-pollution was wild feces and the pollution source was cattle feces. Snails and infectious snails were distributed over the rice fields and the resident was infected through production activities. In plateau basin, the key infection source was human beings. The infection rate in men was higher than that in women. The pattern of water pollution was fertilization. The pollution source was human feces. Snails and infectious snails were distributed over the canals and ditches and the resident was infected through production and daily activities.

CONCLUSIONS

Therefore, it was suggested that the mountainous endemic areas should be divided into two sub-types, i.e., plateau basins and plateau canyons. The different control strategies should be formulated in accordance with the environmental situations and socioeconomic factors in the two kinds of endemic areas.

Tyrosine kinase activation is an immediate and essential step in hypotonic cell swelling-induced ERK activation and c-fos gene expression in cardiac myocytes

Hypotonic stress causes rapid cell swelling and initiates various cellular adaptive processes. However, it is unknown how cells initially sense low osmolarity and convert it into intracellular signals. We investigated the signal transduction mechanism initiated by hypotonic cell swelling in cardiac myocytes using c-fos expression as a nuclear marker. Treatment of myocytes with hypotonic culture media rapidly induced c-fos expression, whereas hypertonic stress had no effect. Transfection of c-fos reporter gene constructs suggested that the hypotonic stress response element maps to the serum response element of the c-fos promoter. Hypotonic stress immediately (within 5 s) activated tyrosine kinase activity, while activation of ERK1/2 peaked at 5 min. Stress-activated kinase (JNK1) was modestly activated at 15 min, whereas HOG1 like kinase (p38) was not activated by hypotonic stress. Extensive pharmacological studies indicated that only tyrosine kinase inhibitors suppressed the hypotonic swelling-induced c-fos expression. The effect of hypotonic stress was mimicked by chlorpromazine, which is known to cause membrane deformation. These results suggest that the signaling mechanism of hypotonic stress is distinct from that of hyperosmolar stress in mammalian cells. Tyrosine kinase activation is the earliest detectable cell response and plays an essential role in hypotonic swelling-induced ERK1/2 activation and c-fos expression.

Oral HIV-I recovery in the presence of periodontal disease

OBJECTIVE

To determine whether a significant association occurs between the presence of various periodontal diseases and recoverable infectious HIV-I in the saliva of injecting drug users.

DESIGN

Five hundred and fifty-one injecting drug users were recruited from various programs associated with the Beth Israel Medical Center. Examiners were 'blinded' to the subject's HIV-I serostatus. A socio-economic and risk factors' survey was conducted and a complete oral examination, including periodontal disease indices was performed. Whole saliva and blood were collected for virus culture.

MAIN OUTCOME MEASUREMENTS

Recovery of infectious HIV-I in saliva related to presence of periodontal diseases.

RESULTS

Those HIV-I seropositive subjects with periodontal diseases did not differ from those HIV-I seropositive subjects without periodontal disease in mean age and immune status. Less than 1% of the HIV-I seropositive subjects had cultivable HIV-I in their saliva while it was present in 78% of PBMCs and 35% of the sera. There was no significant association between infectious HIV-I in saliva, serum, or PBMCs and any of the various periodontal diseases.

CONCLUSIONS

The presence of periodontal disease in HIV-I seropositive injecting drug users does not appear to be a potential risk factor for infectious HIV-I in saliva, probably due to the various anti-viral components of saliva.

Active expression of G gamma globin gene on chromosome 11 with Yunnanese A gamma delta beta)0-thalassemia deletion in MEL cells

A permanent lymphocyte cell line of a heterozygote with Yunnanese (A gamma delta beta)0-thalassemia deletion, associated with an increased production of G gamma globin in adult, was founded using Epstein-Barr virus transformation. The hybrids of the lymphocyte cell and mouse erythroleukemia cell (MEL) were achieved and the hybrids containing human chromosome 11 were selected with the monoclonal antibody 53/6. The subclones containing only either the normal or the abnormal human chromosome 11 were separated and the expression of the human globin genes was studied. Expression of the beta-globin gene, but not the G gamma and A gamma, was observed in the hybrids containing only the normal human chromosome 11, while active expression of the G gamma globin gene was observed in the hybrids containing only the abnormal human chromosome 11. These results have confirmed that the DNA deletion in the beta-globin gene cluster is the cause of persistent active expression of the G gamma globin gene in the Yunnanese mutant.

Identification of domains in rubella virus genomic RNA and capsid protein necessary for specific interaction

In rubella virus-infected cells, genomic 40S and subgenomic 24S RNAs are present in the cytoplasm of infected cells. However, encapsidation by rubella virus capsid protein is specific for 40S genomic RNA. As a first step toward understanding the assembly of rubella virus nucleocapsid at the molecular level, the interaction between capsid protein and genomic RNA was studied by Northwestern (RNA-protein) blot analysis. RNA probes prepared by in vitro transcription were used to localize the RNA sequence that participates in binding to the capsid protein. We have identified a 29-nucleotide RNA sequence (nucleotides 347 to 375) that is essential for the binding. By using overlapping synthetic peptides of capsid protein, a peptide domain (residues 28 to 56) that displays specific RNA-binding activity of capsid protein has been located. This result suggests that the specific recognition of viral RNA during rubella virus assembly involves, at least in part, the nucleocapsid protein.

Cholinergic stimulation modulates negative inotropic effect of cocaine on ferret ventricular myocardium

We tested the hypothesis that the negative inotropic effect (NIE) of cocaine is mediated, at least in part, by cholinergic stimulation and can be correlated with the degree of adenosine 3',5'-cyclic monophosphate (cAMP) dependency of the inotropic state. Cardiac myocytes were isolated from left ventricles of ferrets and loaded with the fluorescent Ca2+ indicator indo 1. Cells were placed in physiological solution containing 2.0 mM Ca2+ and stimulated at 0.5 Hz and 30 degrees C. Cocaine decreased peak cell shortening and peak intracellular Ca2+ in a concentration-dependent manner (10(-8)-10(-4) M). The concentration-response curve of cocaine was shifted significantly downward compared with those of lidocaine and procaine in the same range of concentrations. Atropine (10(-6) M) shifted the concentration-response curve of cocaine, but not those of lidocaine and procaine, rightward, with a pA2 value (7.66) similar to that obtained with carbachol (7.99). With prior addition of isoproterenol (ISO, 10(-8) M) or increased Ca2+ (4.0 mM) to increase cell shortening to the same degree (approximately 60%), cocaine and carbachol decreased contractility to a significantly greater extent in ISO-stimulated myocytes. To clarify whether these treatments changed responsiveness of the contractile elements to Ca2+, the effect of 2,3-butanedione monoxime, an agent that interferes with the interaction of myosin and actin, was tested with previous addition of ISO or increased Ca2+, and no differential effect occurred. Therefore, we postulate that 1) the NIE of cocaine on myocytes is caused by decreased Ca2+ availability; 2) this effect is due to specific stimulation of cholinergic receptors in addition to other direct myocardial (probably local anesthetic) effects; and 3) the NIE correlates with the level of cAMP dependence of the inotropic state.

Interleukin-6 selectively enhances the intracellular calcium response to NMDA in developing CNS neurons

Increasing evidence supports a role for cytokines as chemical signals in the CNS, either under normal conditions or in the pathologic state. CNS levels of the cytokine interleukin-6 (IL-6) are known to be elevated in several diseases associated with developmental disorders and may contribute to the pathological state. To investigate the potential role of IL-6 in such disorders, neuronal effects of IL-6 were examined during development using an in vitro model system, cultured rat cerebellar granule neurons. The cultures were prepared from 8 d postnatal rat pups and exposed chronically to IL-6 (5 ng/ml) by addition to the culture medium. Neuronal effects of IL-6 were assessed by a comparison of calcium signals produced in control and IL-6 treated neurons by the glutamate receptor agonists NMDA and domoate and by K+ depolarization. IL-6 treatment significantly enhanced the response to NMDA and altered the developmental pattern of NMDA sensitivity, whereas only minor changes were observed for the response to domoate and K+. Reducing extracellular calcium and depleting intracellular stores significantly decreased the amplitude of the response to NMDA in control and IL-6 treated neurons. However, the IL-6 treated neurons were significantly more sensitive to these treatments than control neurons. These results suggest that elevated levels of IL-6 can significantly alter CNS neuron development and response to excitatory transmitters, and that IL-6 pretreatment selectively enhances the intracellular calcium responses to NMDA by altering the relative contribution of extracellular calcium influx and release of calcium from stores to the calcium signal.

[Surgical treatment of primary cardiac tumors]

From Jan. 1962 to Nov. 1994, 130 patients with primary cardiac tumors were performed in Shanghai Chest Hospital. There were 48 male and 82 female patients ranging in age from 16 to 73 (average 43.8 years). 123 (94.6%) had benign and 7 (5.4%) were malignant tumor. Cardiac myoxmas accounted for 91.1% of all benign neoplasias. 5 patients with benign and 1 patient with malignant tumor died early (within 30 days of operation). Of the 4 patients who died late, 3 had had malignant disease.

Brefeldin A and monensin arrest cell surface expression of membrane glycoproteins and release of rubella virus

The maturation of rubella virus (RV) glycoproteins E2 and E1 was examined by using brefeldin A (BFA) and monensin. BFA, which induces the rapid redistribution of Golgi enzymes residing in the Golgi complex into the endoplasmic reticulum (ER), was used to locate the intracellular site for the modification of carbohydrate side-chains on RV E1 and E2 proteins. The monovalent ionophore monensin, which inhibits intracellular transport of proteins through the ER-Golgi complex, was used to block the transport of E1 and E2 glycoproteins through the Golgi complex. BFA and monensin effectively blocked the cell surface expression of RV E2 and E1 proteins, secretion of an anchor-free form of E2 and budding of RV from the plasma membrane. For O-linked glycosylation, addition of N-acetylgalactosamine and galactose to E2 protein was found to take place in the medial to the trans Golgi. A dramatic change in the intracellular distribution of RV structural proteins was observed when transfected COS cells were treated with BFA or monensin, although the proteolytic processing of RV structural protein precursor was not affected. In the presence of BFA or monensin, virus release from infected Vero cells was only 0.1% of the intracellular virus, and the intracellular virus titre decreased as well. Our results suggest that O-linked glycosylation on the E2 protein occurred in the post-ER region and the transport of RV structural proteins to the Golgi complex and post-Golgi compartment may be a rate-limiting step in RV assembly and budding.

Angiotensin II and other hypertrophic stimuli mediated by G protein-coupled receptors activate tyrosine kinase, mitogen-activated protein kinase, and 90-kD S6 kinase in cardiac myocytes. The critical role of Ca(2+)-dependent signaling

Many hypertrophic stimuli such as angiotensin II (Ang II) activate phospholipases through G protein-coupled receptors in cardiac myocytes. However, it is not known whether these stimuli also activate the tyrosine phosphorylation-dependent signaling pathway, which plays an essential role in growth factor-induced mitogenic responses in other cell types. Serine/threonine kinases such as mitogen-activated protein (MAP) kinases and 90-kD S6 kinase (RSK) are activated in response to many growth stimuli and are important downstream signaling pathways of tyrosine kinases. Therefore, we examined whether Ang II activates these protein kinases in primary cultures of cardiac myocytes and fibroblasts from neonatal rats. Ang II rapidly induced tyrosine phosphorylation of multiple proteins, including 42-, 44-, 75- to 80-, and 120- to 130-kD proteins, in both cardiac myocytes and fibroblasts. This was accompanied by an increase in tyrosine kinase activity. The 42- and 44-kD proteins were immunologically related to an extracellular signal-regulated kinase family (MAP kinases). Ang II rapidly increased kinase activity of MAP kinases and their downstream kinase, RSK. The Ang II-induced tyrosine phosphorylation and activation of MAP kinases and RSK were AT1 receptor-mediated. Activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate or an increase in intracellular Ca2+ by the Ca2+ ionophore A23187 was sufficient to cause tyrosine phosphorylation of multiple proteins and activation of MAP kinase and RSK. Although downregulation of PKC did not suppress Ang II-induced activation of MAP kinase and RSK, chelating intracellular Ca2+ by BAPTA-AM completely abolished Ang II-induced activation of these kinases. Activation of MAP kinases and RSK was also observed in myocytes stimulated with other agonists for Gq protein-coupled receptors, such as phenylephrine, norepinephrine, and endothelin 1, but not with agonists to Gs protein-coupled receptors, such as isoproterenol. These results suggest that Ang II and other hypertrophic stimuli, known to act through Gq protein-coupled receptors, rapidly cause tyrosine phosphorylation of several intracellular substrates through activation of tyrosine kinase and activate MAP kinases and RSK in cardiac myocytes as well as in cardiac fibroblasts. Furthermore, intracellular Ca2+, rather than PKC, seems to be critical for Ang II-induced activation of these protein kinases in cardiac myocytes.

Ca2+ handling and myofibrillar Ca2+ sensitivity in ferret cardiac myocytes with pressure-overload hypertrophy

Experiments were performed in aequorin-loaded left ventricular myocytes isolated from hypertrophied hearts and age-matched controls. Five to six months after postvalvular aortic banding, left ventricular hypertrophy was present, as indicated by a 97% (P < 0.001) increase in the left ventricular weight-to-body weight ratio and a 24% (P < 0.001) increase in cell width. In comparison with controls, the hypertrophied myocytes demonstrated that 1) contraction duration was prolonged by 37% (P < 0.001) and was associated with a 44% (P < 0.001) prolongation of the intracellular Ca2+ transient; 2) peak systolic shortening was decreased by 31% (P < 0.001) and was associated with a 21% (P < 0.001) decrease in peak systolic intracellular Ca2+ concentration; 3) both the peak systolic intracellular Ca2+ concentration-to-peak shortening relationship and the intracellular Ca2+ concentration-to-cell shortening relationship at the time of the peak twitch were shifted downward, suggesting a decrease in myofilament Ca2+ responsiveness; and 4) isoproterenol (5 x 10(-8) M) produced equal increases in the peak systolic intracellular Ca2+ of control and hypertrophied myocytes (88 vs. 90%; P > 0.05) in contrast to much smaller increases in the peak cell shortening (170 vs. 73%; P < 0.02) of the hypertrophied myocytes, suggesting a decrease in myofilament Ca2+ responsiveness. These data demonstrate that the hypertrophy-related abnormalities in intracellular Ca2+ handling and mechanical function, previously reported in aequorin-loaded multicellular muscle preparations, are present in isolated myocytes, arguing against changes in the interstitium as essential causative factors.

Expression and characterization of virus-like particles containing rubella virus structural proteins

Rubella virus (RV) virions contain two envelope glycoproteins (E1 and E2) and a capsid protein (C). Noninfectious RV-like particles (VLPs) containing three structural proteins were expressed in a BHK cell line (BHK-24S) by using an inducible promoter. These VLPs were found to resemble RV virons in terms of their size, their morphology, and some biological activities. In immunoblotting studies, VLPs were found to bind similarly to native RV virions with 10 of a panel of 12 RV-specific murine monoclonal antibodies. Immunization of mice with VLPs induced specific antibody responses against RV structural proteins as well as virus-neutralizing and hemagglutination-inhibiting antibodies. After immunization of mice with VLPs, in vitro challenge of isolated lymphocytes with inactivated RV and individual RV structural proteins stimulated proliferation. Our data suggest the possibility of using VLPs as immunogens for serodiagnostic assays and RV vaccines.

Mutational analysis of the arginine residues in the E2-E1 junction region on the proteolytic processing of the polyprotein precursor of rubella virus

Endoproteolytic cleavage of precursors is a key step in biosynthesis of functional proteins. The structural proteins of rubella virus are initially translated as a precursor polyprotein in the order NH2-C-E2-E1-COOH and are cleaved by host signal peptidase to yield three structural proteins. Between regions corresponding to E2 and E1 in the precursor is a region of seven amino acid residues (R-R-A-C-R-R-R) that contains a motif for stop-transfer or a possible target for trypsin-like protease cleavage. Using site-directed mutagenesis, these arginine residues, as well as the signal peptide cleavage site at the N-terminus of E1, have been mutated individually or in combination. Results from in vitro transcription/translation analysis indicated that the mutated E2E1 precursor polyproteins were translocated into the microsome and glycosylated. Expression of mutated precursor polyproteins in COS cells revealed that the cleavage of E2E1 polyprotein precursor was impaired when the signal peptide cleavage site alone or both arginine clusters were altered, whereas partial cleavage was observed in the mutants in which either one of the two arginine clusters was modified. Our data suggest that although the arginine clusters do not function as a basic protease cleavage site, they contribute to maintain the proper configuration of that region for access of cellular signal peptidase.

Differential effects of cocaine and cocaethylene on intracellular Ca2+ and myocardial contraction in cardiac myocytes

1. Isolated cardiac myocytes of the ferret were used to investigate the influence of cocaine and cocaethylene on the intracellular Ca2+ transient indicated by the indo-1 405/480 nm ratio signal, and peak cell shortening. 2. Both cocaine and cocaethylene produced significant decreases in peak intracellular Ca2+ and peak cell shortening in a dose-dependent manner. Of interest, (1) the minimally effective dose of cocaethylene was ten fold lower (10(-8)M versus 10(-7)M) than that of cocaine; (2) the log EC50 of cocaethylene was -5.99 +/- 0.13 (1.0 x 10(-6) M), which was about ten fold lower than that of cocaine (-5.02 +/- 0.11, 9.6 x 10(-6) M); and (3) 1 x 10(-4)M cocaethylene decreased the contraction amplitude by 71 +/- 7%, while the same concentration of cocaine decreased the amplitude only by 55 +/- 5%, indicating that cocaethylene is more potent than cocaine. 3. The negative inotropic effects of either cocaine or cocaethylene could be overcome by noradrenaline (approximately 5 microM) or calcium. 4. In contrast to cocaine, cocaethylene shifted the peak [Ca2+]i-peak shortening relationship downward, indicating that cocaethylene decreased myofilament Ca(2+)-responsiveness. 5. These data indicate that both cocaine and cocaethylene act directly on cardiac myocytes to produce a negative inotropic effect that is due to decreased Ca2+ availability. In contrast to cocaine, cocaethylene produces more potent inhibition by an additional action to decrease myofilament Ca(2+)-responsiveness.

The influence of N-linked glycosylation on the antigenicity and immunogenicity of rubella virus E1 glycoprotein

Rubella virus E1 glycoprotein contains three functional N-linked glycosylation sites. The role of N-linked glycosylation on the antigenicity and immunogenicity of E1 glycoprotein was studied using vaccinia recombinants expressing E1 glycosylation mutants. Expressed E1 glycosylation mutant proteins were recognized by a panel of E1-specific monoclonal antibodies in radioimmunoprecipitation, immunofluorescence, and immunoblotting, indicating that carbohydrate side chains on E1 are not involved in the constitution of epitopes recognized by these monoclonal antibodies. This observation was further supported by the fact that removal of oligosaccharides on E1 by glycosidase digestion did not significantly change the antigenicity of E1. All the glycosylation mutants were capable of eliciting anti-RV E1 antibodies. The single glycosylation mutants (G1, G2, and G3), but not the double mutant (G23) or the triple mutant (G123), were found to be capable of inducing virus neutralizing antibodies. Among the single glycosylation mutants, only G2 and G3 were active in producing hemagglutination inhibition antibodies in mice. Our findings suggest that although carbohydrate on E1 is not directly involved in the antigenic structures of E1, it is important in maintaining proper protein folding and stable conformation for expression of immunological epitopes on E1.

Role of N-linked oligosaccharides in processing and intracellular transport of E2 glycoprotein of rubella virus

The role of N-linked glycosylation in processing and intracellular transport of rubella virus glycoprotein E2 has been studied by expressing glycosylation mutants of E2 in COS cells. A panel of E2 glycosylation mutants were generated by oligonucleotide-directed mutagenesis. Each of the three potential N-linked glycosylation sites was eliminated separately as well as in combination with the other two sites. Expression of the E2 mutant proteins in COS cells indicated that in rubella virus M33 strain, all three sites are used for the addition of N-linked oligosaccharides. Removal of any of the glycosylation sites resulted in slower glycan processing, lower stability, and aberrant disulfide bonding of the mutant proteins, with the severity of defect depending on the number of deleted carbohydrate sites. The mutant proteins were transported to the endoplasmic reticulum and Golgi complex but were not detected on the cell surface. However, the secretion of the anchor-free form of E2 into the medium was not completely blocked by the removal of any one of its glycosylation sites. This effect was dependent on the position of the deleted glycosylation site.

Effects of endothelin on intracellular Ca2+ and contractility in single ventricular myocytes from the ferret and human

We investigated the role of endothelin-1 on peak intracellular Ca2+ ([Ca2+]i) and peak shortening of ventricular myocytes (loaded with indo-1/AM) from failing human hearts. 10 nM of ET-1 significantly increased the cell peak shortening (84 +/- 29%, P less than 0.05) without significantly increasing the peak [Ca2+]i (15 +/- 7%, P greater than 0.05). Further studies on ferret cardiac myocytes indicated that in addition to producing dose-dependent (0.1-10 nM) significant increases in peak shortening (max 55 +/- 6% P less than 0.01) and non-significant increases in peak [Ca2+]i (max 35 +/- 19%, P greater than 0.05), endothelin-1 significantly shifted the peak [Ca2+]i-peak shortening curve upward. The results suggest that endothelin-1 acts directly on human and ferret cardiac myocytes to produce a positive inotropic effect that may predominantly be due to an enhanced myofilament Ca2+ responsiveness.

Purification and properties of poly(ADPribose) synthetase from sheep testis

Poly(ADPribose) synthetase has been purified to apparent homogeneity from sheep testis by a simple procedure using three chromatographic steps (DNA-agarose, blue Sephadex G-150 and phosphocellulose P11). A concentrated enzyme preparation, 3.5 mg, with a specific activity of 1265 nmol/min per mg was obtained from 250 g of tissue. DNA was absolutely required for enzyme activity. The half-maximal activation occurred at the concentrations of 11 micrograms/ml for highly polymerized calf thymus DNA and 2 micrograms/ml for sonicated calf thymus DNA. The Km for NAD was 57 microM. The molecular weight was 120 000, determined by gel electrophoresis in the presence of sodium dodecyl sulfate. Amino acid analysis indicated that the main amino acid species of sheep testis enzyme were very similar to those of enzymes from other sources.