Identification, cloning, and expression of the Escherichia coli pyrazinamidase and nicotinamidase gene, pncA

Pyrazinamide (PZA) is one of the three most important drugs for treatment of Mycobacterium tuberculosis infections. The antibacterial activity of PZA requires a bacterial enzyme, pyrazinamidase (PZAase), which hydrolyzes PZA to form pyrazinoic acid and ammonia. Most PZA-resistant clinical M. tuberculosis isolates lack PZAase activity. With the goal of eventually identifying and characterizing the M.tuberculosis PZAase gene, we began with the more tractable organism, Escherichia coli, which also has PZAase activity. We screened a transposon-generated E. coli insertion mutant library, using a qualitative PZAase assay. Two PZAase-negative mutants out of 4,000 colonies screened were identified. In each mutant, the transposon interrupted the same 639-bp open reading frame (ORF), ORF1. The expression of ORF1 on a multicopy plasmid complemented a PZAase-negative mutant, leading to PZAase activity levels approximately 10-fold greater than those of the wild type. PZA has a structure similar to that of nicotinamide, a pyridine nucleotide cycle intermediate, so we tested our strains for nicotinamidase activity (EC 3.5.1.19) (genetic locus pncA). The construct with multiple plasmid copies of ORF1 had an approximately 10-fold increase in levels of nicotinamidase activity. This overexpressing strain could utilize nicotinamide as a sole nitrogen source, through wild-type E. coli cannot. We conclude that a single E. coli enzyme accounts for both PZAase and nicotinamidase activities and that ORF1 is the E.coli PZAase and nicotinamidase gene, pncA.

Covalent modification of rat liver dipeptidyl peptidase IV (CD26) by the nonsteroidal anti-inflammatory drug diclofenac

Diclofenac is a nonsteroidal anti-inflammatory drug that has been implicated in several cases of severe hepatotoxicity. Our previous study showed that diclofenac metabolites bound covalently and selectively to rat liver plasma membrane proteins with estimated monomeric masses of 110, 140, and 200 kDa. We report here that we have identified the 110 kDa diclofenac-labeled protein in rat liver as dipeptidyl peptidase IV, also known as CD26. In addition, we found that the activity of dipeptidyl peptidase IV in liver plasma membrane fractions was lowered after diclofenac treatment of rats. These results suggest that the hepatotoxicity associated with diclofenac might be due, in part, to the covalent modification of dipeptidyl peptidase IV.

cDNA cloning and baculovirus expression of the human liver endoplasmic reticulum P58: characterization as a protein disulfide isomerase isoform, but not as a protease or a carnitine acyltransferase

The function of a 58-kDa liver microsomal protein (P58) is controversial. To help clarify the physiological function of this protein, particularly in humans, a full-length human liver cDNA clone was isolated, sequenced, and expressed in milligram quantities with the use of a baculovirus expression system. The deduced amino acid sequence of the mature protein contained two thioredoxin-like active site motifs (CGHC) and in its C-terminus a nuclear localization motif (KPKKKKK), and an ER-retention/retrieval motif (QEDL). The mature form of human P58 shared 95% amino acid sequence identity with the deduced amino acid sequences of a bovine liver cDNA, 93% with a murine B lymphocyte cDNA, and 91% with a rat basophilic leukemia cell cDNA. In contrast to reports on the activities of nonhuman forms of P58, the purified expressed human P58 showed no carnitine acyltransferase or protease activities. However, it did have protein disulfide isomerase activity, indicating that the physiological activity of human liver P58 may be attributed, at least in part, to this activity.

Effects of incidental infections and immune activation on disease progression in experimentally feline immunodeficiency virus-infected cats

Specific pathogen-free cats were experimentally infected with feline immunodeficiency virus (FIV) and subsequently exposed to common infectious pathogens and immune stimuli over a 3-year period. Cats with preexisting FIV infection showed signs of disease after exposure to Haemobartonella felis, Toxoplasma gondii, feline herpesvirus-1, and feline calicivirus similar to signs in non-FIV-infected cats, although they were more severe. No adverse effects of immunization with inactivated rabies virus vaccine and a synthetic polyproline immunogen were observed in either FIV-infected or non-FIV-infected cats, whereas the application of a diphtheria-tetanus-pertussis vaccine caused transient fever and lymphadenopathy in both groups of animals. Primary immune responses to pathogens or immunogens were usually delayed or diminished in FIV-infected compared with non-FIV-infected cats. Repeated infections and immune activation had no significant effects on the levels of FIV-specific antibodies or on the proportion of peripheral blood mononuclear cells (PBMCs) containing FIV proviral DNA. However, FIV-infected cats that were not exposed to immune stimuli had lower CD4+ T-lymphocyte numbers and lower CD4+/CD8+ T lymphocyte ratios at the end of the 3-year study than FIV-infected cats exposed to cofactors. The latter also had normal levels of interleukin-3 receptor (IL-2R) and major histocompatibility class II (MHC-II) antigen expression on PBMCs, while FIV-infected cats not exposed to cofactors had up-regulated IL-2R and down-regulated MHC-II antigen expression. It was concluded that repeated immune stimulation did not have a deleterious effect on the course of FIV-induced immunodeficiency.

Effect of chronic feline immunodeficiency virus infection on experimental feline calicivirus-induced disease

Acute feline calicivirus (FCV) infection caused a more severe disease in chronically feline immunodeficiency virus (FIV) infected than in non-FIV infected cats. FIV infected cats shed significantly higher amounts of FCV through their saliva after FCV challenge than the non-FIV infected cats. However, there was no difference in the duration of FCV shedding. None of the cats exposed to FCV developed chronic FCV carriage. Both groups of cats mounted similar titers of neutralizing antibodies to FCV. Although FIV infected cats started out with significantly lower total lymphocyte and neutrophil numbers than the non-FIV infected cats, the transient lymphopenia and neutrophilia attributable to the FCV infection was of similar intensity in both groups of animals. There was no evidence that the underlying FIV-related disease or viremia was influenced by acute FCV infection. Acute FCV infection did not significantly alter the CD4+/CD8+ T lymphocyte ratio in FIV infected compared to non-FIV infected cats. The ongoing humoral IgG response to FIV was not affected by the FCV infection. There was no significant change in the proportion of FIV infected peripheral blood mononuclear cells during 8 subsequent weeks after FCV challenge as determined by polymerase chain reaction.

A dominant negative allele of the Escherichia coli uvrD gene encoding DNA helicase II. A biochemical and genetic characterization

A site-specific lysine to methionine mutation has been engineered at the invariant Lys35 residue in the ATPase A binding site of the Escherichia coli uvrD gene encoding DNA helicase II. The mutant protein (UvrDK35M) has been purified to apparent homogeneity and characterized. The kcat for DNA-dependent ATP hydrolysis was less than 0.5% that of the wild-type enzyme with no change in the apparent Km for ATP. No unwinding of partial duplex DNA substrates could be detected using the mutant protein. Moreover, the mutant protein inhibited the unwinding reaction catalyzed by the wild-type protein at ratios of mutant enzyme to wild-type enzyme < 1. We conclude that the K35M mutation renders helicase II catalytically inactive as a DNA helicase with little or no effect on the ability of the enzyme to bind ATP, DNA, or other proteins. In vivo complementation assays indicate that the mutant protein cannot substitute for the wild-type protein in methyl-directed mismatch repair, suggesting that the ATPase and/or helicase activity of helicase II is required in this repair pathway. Additional genetic characterization of the uvrDK35M allele, supplied on a plasmid, suggests that expression of the mutant protein, at levels equivalent to that of the wild-type protein, results in a dominant negative phenotype. Expression of lower levels of the mutant protein, both in the presence and absence of wild-type helicase II, results in a constitutive induction of the cellular SOS response and extensive filamentation of cells. This induction of the SOS response is not due to a defect in methyl-directed mismatch repair. Taken together, these data are consistent with the notion that E. coli helicase II may have a role in DNA replication.

DNA helicases: enzymes with essential roles in all aspects of DNA metabolism

DNA helicases catalyze the disruption of the hydrogen bonds that hold the two strands of double-stranded DNA together. This energy-requiring unwinding reaction results in the formation of the single-stranded DNA required as a template or reaction intermediate in DNA replication, repair and recombination. A combination of biochemical and genetic studies have been used to probe and define the roles of the multiple DNA helicases found in E. coli. This work and similar efforts in eukaryotic cells, although far from complete, have established that DNA helicases are essential components of the machinery that interacts with the DNA molecule.

Prevalence and risk factors for iron deficiency anemia in weanling rhesus macaques

Standard epidemiologic methods were used to determine the prevalence and risk factors for iron deficiency at weaning in 143 weanling rhesus macaques (Macaca mulatta) raised indoors at the California Primate Research Center, Davis, CA. Maternal, infant, and management factors were investigated. Prevalence of iron deficiency anemia was 19%, as defined by mean corpuscular volume less than or equal to 66 femtoliters. It was found that animals raised entirely or partially in the nursery had less iron deficiency than dam-reared offspring. Results also suggest multiparous dams were more likely to have iron-deficient weanlings than primiparous dams. These results were discussed in relation to human and nonhuman primate pediatric medicine.

The effect of age on the course of experimental feline immunodeficiency virus infection in cats

Neonatal, young adult, and aged specific pathogen-free cats were experimentally infected with cat-passaged Petaluma strain of feline immunodeficiency virus. The primary stage of illness occurred 6-8 weeks following infection in cats of all ages, but it differed in severity and clinical signs. Generalized lymphadenopathy persisted for the entire 42-week study period in neonatally infected cats, was transient in young adults, but inapparent in aged cats. Only two aged cats became chronically and severely ill during the study. One aged cat died with severe necrotizing transmural enteritis, while a second developed chronic generalized staphylococcal pyoderma that was partially controlled with antibiotics. Neutropenia appeared 6-8 weeks following infection in cats of all ages, but was more severe in newborn and aged cats than in young adults. A persistent decrease in CD4+/CD8+ T lymphocyte ratios, due to both increased CD8+ and decreased CD4+ T lymphocytes, occurred in the neonatal and aged cats. Decreased CD4+/CD8+ T lymphocyte ratios in the young adult cats was due solely to decreased CD4+ T lymphocytes. Antibody response to FIV virus, as measured by ELISA to recombinant FIV p24 antigen, was lower in aged cats than the other age groups during the first 6 weeks after infection. Antibody levels were not significantly different among the three age groups thereafter. Although there are some differences between FIV infection of cats and HIV infection of human beings, age at infection influences the severity of disease in both species.

Interaction of acute feline herpesvirus-1 and chronic feline immunodeficiency virus infections in experimentally infected specific pathogen free cats

Cats with or without chronic feline immunodeficiency virus (FIV) infection were exposed to feline herpesvirus, type 1 (FHV-1). FIV infected cats became sicker than non-FIV infected cats and required more supportive treatment. However, there were no differences in the length of their illness or in the levels and duration of FHV-1 shedding. FHV-1 infection caused a transient neutrophilia at Day 7 with a rapid return to preinfection levels. The neutrophilia coincided with a transient lymphopenia that was accompanied by a decline in both CD4+ and CD8+ T-lymphocytes. A brief decrease in the CD4+/CD8+ T-lymphocyte ratio occurred at Day 14 in both FIV infected and non-infected cats. This decrease was mainly the result of an absolute and transient increase in CD8+ T-lymphocytes. CD4+ and CD8+ T-lymphocyte numbers and CD4+/CD8+ T-lymphocyte ratios returned to baseline within 4-8 weeks in both FIV infected and non-infected cats. FIV infected cats produced less FHV-1 neutralizing antibodies during the first 3 weeks of infection than non-FIV infected animals. The IgM FHV-1 antibody response was depressed in FIV infected cats whereas the IgG antibody response was unaffected. FHV-1 infection evoked a comparable transient loss of lymphocyte blastogenic responses to concanavalin A and pokeweed mitogen in both FIV infected and non-infected cats. However, response to pokeweed mitogen took longer to return to normal in FIV infected animals. Lymphocytes from FIV infected cats had a greater and more sustained proliferative response to FHV-1 antigen than non-FIV infected cats. The ongoing IgG antibody response to FIV was not affected by FHV-1 infection.

Escherichia coli Rep protein and helicase IV. Distributive single-stranded DNA-dependent ATPases that catalyze a limited unwinding reaction in vitro

Rep protein and helicase IV, two DNA-dependent adenosine 5'-triphosphatases with helicase activity, have been purified from Escherichia coli and characterized. Both enzymes exhibit a distributive interaction with single-stranded DNA as DNA-dependent ATPases in a reaction that is relatively resistant to increasing NaCl concentration and sensitive to the addition of E. coli single-stranded DNA binding protein (SSB). The helicase reaction catalyzed by each protein has been characterized using a direct unwinding assay and partial duplex DNA substrates. Both Rep protein and helicase IV catalyzed the unwinding of a duplex region 71 bp in length. However, unwinding of a 119-bp or 343-bp duplex region was substantially reduced compared to unwinding of the 71-bp substrate. At each concentration of protein examined, the number of base pairs unwound was greatest using the 71-bp substrate, intermediate with the 119-bp substrate and lowest using the 343-bp substrate. The addition of E. coli SSB did not increase the fraction of the 343-nucleotide fragment unwound by Rep protein. However, the addition of SSB did stimulate the unwinding reaction catalyzed by helicase IV approximately twofold. In addition, ionic strength conditions which stabilize duplex DNA (i.e. addition of MgCl2 or NaCl), markedly inhibited the helicase reaction catalyzed by either Rep protein or helicase IV while having little effect on the ATPase reaction. Thus, these two enzymes appear to share a common biochemical mechanism for unwinding duplex DNA which can be described as limited unwinding of duplex DNA. Taken together these data suggest that, in vitro, and in the absence of additional proteins, neither Rep protein nor helicase IV catalyzes a processive unwinding reaction.

Inhibition of DNA helicase II unwinding and ATPase activities by DNA-interacting ligands. Kinetics and specificity

Although DNA helicases play important roles in the processing of DNA, little is known about the effects of DNA-interacting ligands on these helicases. Therefore, the effects of a wide variety of DNA-binding ligands on the unwinding and ATPase reactions catalyzed by Escherichia coli DNA helicase II were examined. DNA minor groove binders and simple DNA intercalators did not inhibit helicase II. However, DNA intercalators, such as mitoxantrone and nogalamycin, which position functionalities in the major groove upon binding duplex DNA, were potent inhibitors of helicase II. To determine the mechanism by which mitoxantrone inhibited helicase II, the unwinding and DNA-dependent ATPase activities of helicase II were measured using a spectrum of double- and single-stranded DNA substrates. Using either a 71-base pair (bp) M13mp7 partially duplexed DNA substrate or a 245-bp bluntended, fully duplexed DNA substrate, the apparent Ki value for inhibition by mitoxantrone of both the unwinding and ATPase reactions was approximately 1 microM for both substrates, suggesting that the mechanism of inhibition of helicase II by mitoxantrone is the same for both substrates and requires the presence of double-stranded structure. To strengthen this conclusion, the ability of mitoxantrone to inhibit the DNA-dependent ATPase activity of helicase II was determined using two single-stranded substrates, poly(dT) and the 245-bp substrate after heat denaturation. Using either substrate, mitoxantrone inhibited the ATPase activity of helicase II far less effectively. Thus, these results indicate that the intercalation of mitoxantrone into double-stranded DNA, with accompanying placement of functionalities in the major groove, generates a complex that impedes helicase II, resulting in both inhibition of ATP hydrolysis and unwinding activity. Furthermore, we report here that DNA-binding ligands inhibit the unwinding activity of helicases I and IV and Rep protein from E. coli, demonstrating that the inhibition observed for helicase II is not unique to this enzyme.

Progressive immune dysfunction in cats experimentally infected with feline immunodeficiency virus

Within 6 months of infection with the Petaluma isolate of feline immunodeficiency virus, specific-pathogen-free domestic cats exhibited a decrease in the percentage and number of circulating CD4+ lymphocytes and in the CD4+/CD8+ T-cell ratio, along with a marginally significant depression of pokeweed mitogen-induced lymphocyte proliferation in vitro. There was no loss of responsiveness to concanavalin A during this stage, and the cats were capable of mounting a satisfactory antibody response to a T-dependent, synthetic polypeptide immunogen. The pokeweed mitogen response deficit became clearly demonstrable by 11 to 12 months postinfection. A decline in the lymphocyte proliferative response to concanavalin A and a diminished ability to mount an in vivo antibody response to the T-dependent immunogen evolved by 25 to 44 months postinfection. Virus infection did not affect the ability of cats to mount an antibody response to a T-independent synthetic polypeptide immunogen. These data indicate that feline immunodeficiency virus produces a slowly progressive deterioration of T-cell function but does not affect the ability of B cells to recognize and respond to a T-independent antigenic stimulus.

Endogenous bilirubin excretion in Bolivian squirrel monkeys with a Gilbert's-like syndrome

Fasted Bolivian squirrel monkeys (BoSM) exhibit a marked hyperbilirubinemia when compared to fed BoSM. This fasting hyperbilirubinemia (FH) is similar to that in human patients with Gilbert's syndrome. Endogenous bilirubin (BR) excretion (production) into bile was elevated two-fold in BoSM upon fasting. The fraction of injected dose of 3 H-amino-levulinic acid (ALA) incorporated into biliary BR in fasted monkeys was of less magnitude than in fed monkeys and was associated with lower specific activities of 3 H-BR. Both the lower incorporation of ALA and lower specific activities of 3H-BR in fasted BoSM suggest that increased BR excreted may have arisen from pre-existing non-labeled pools of either heme or BR.

Effect of repeated phlebotomy on iron status of rhesus monkeys (Macaca mulatta)

Iron status, as determined by hematologic values, serum iron concentration, total iron-binding capacity, and zinc protoporphyrin concentration, was determined in 2 groups of 6 nonpregnant monkeys. Monkeys of groups 1 and 2 had 10 and 5%, respectively, of their blood volume withdrawn per week for up to 10 weeks or until blood hemoglobin concentration was less than or equal to 10 g/dl. A third group of 6 monkeys served as controls. The majority (8/12) of the monkeys became anemic (hemoglobin concentration, less than or equal to 10 g/dl) after approximately 30 to 70% (mean, 49%) of their blood volume was removed. Anemia was accompanied by decrease in serum iron concentration and percentage of transferrin saturation. Microcytosis, hypochromasia, and increased zinc protoporphyrin concentration, all hematologic characteristics of iron deficiency, developed later. The calculated iron stores ranged from 1 to 133 mg, with mean value of 51 mg. Iron-depleted monkeys had mean calculated available iron store of 20.8 mg, whereas iron-replete monkeys had mean available iron store of 114.0 mg. Changes were not observed in monkeys of the control group during the study period. None of the baseline hematologic or biochemical analytes measured were good predictors of iron stores. The diet used at the research center did not provide sufficient iron to prevent iron deficiency in most of the monkeys from which a total amount of 30 to 70% of blood volume at 5 or 10%/week was withdrawn. Studies requiring that much blood may need to be modified to include iron supplementation, reduction of sample volume, or iron replacement after termination of projects.

Age-related differences in erythropoietic response to recombinant human erythropoietin: comparison in adult and infant rhesus monkeys

Human recombinant erythropoietin (r-HuEPO) was given i.v. to rhesus monkeys to compare its safety, erythropoietic effects, and pharmacokinetics in healthy adult and infant animals. Eighteen adult and 18 infant (9- to 15-d-old) monkeys were divided into three groups each of six animals. One group was given 250 U/kg twice weekly, another was given 100 U/kg twice weekly, and a control group was given the drug vehicle for 6 wk. All animals were healthy throughout this period, and for 10 wk after that. Administration of r-HuEPO at these dosages did not produce any changes in leukocytes, platelets, urea nitrogen, bilirubin, creatinine, alkaline phosphatase, alanine amino transferase, gamma-glutamyl transferase, and blood pressure in either age group. At 6 wk, both adult treatment groups had statistically significant increases in Hb concentration. The same dosages that produced these increases in Hb concentration in adults produced no changes in Hb concentration in infant monkeys. Despite active erythropoiesis, as determined by reticulocytosis and increased total body Hb, Hb concentration decreased similarly in the infant treatment and control groups. Pharmacokinetic profiles were obtained at 5 wk of dosing. One h after administration, both doses of r-HuEPO produced significantly lower serum r-HuEPO concentration in the infant monkeys compared with the adults. These differences appeared to be due to a larger volume of distribution of r-HuEPO in the infant monkeys. The t1/2 of r-HuEPO in circulation was the same in both age groups.

Electrolyte abnormalities associated with diarrhea in rhesus monkeys: 100 cases (1986-1987)

Serum electrolyte values from 100 rhesus monkeys with diarrhea were reviewed. The most frequent finding was hyponatremia (88%), with hypochloremia next most frequently detected (80%). Metabolic acidosis was less common (59%) and usually associated with high anion gap values. Associations between electrolyte abnormalities and age, housing, or case outcome were not found. Bacteriologic culturing was performed on fecal specimens from 90 monkeys. Campylobacter coli or C jejuni alone was isolated from 42 (46.7%) specimens, C coli and Shigella flexneri were isolated from 25 (27.8%) specimens, and S flexneri alone was isolated from 6 (6.7%) specimens. A pathogen was not isolated from 17 (18.9%) specimens. Hyponatremia, hypochloremia, acidosis, and high anion gap values were most severe in monkeys infected with Campylobacter sp, either alone or with concurrent S flexneri infection. Serum sodium concentrations less than 132 mEq/L and serum Cl concentrations less than 93 mEq/L were consistently associated with Campylobacter sp infection.

Biliverdin reductase activity in cattle, sheep, rabbits and rats

1. Biliverdin reductase (BVR) activity was measured in post-microsomal supernatants of livers of cattle, sheep, rabbits and rats. BVR activities in bovine and ovine livers were 4.7 and 5.0%, respectively, of rat liver activity. 2. The finding of BVR activity in ruminants is in contrast to a previous report and may be due to the use of a different assay system. 3. Lapine liver had the lowest BVR activity of only 0.37% of rat liver activity. 4. Increasing the available heme by phenylhydrazine administration did not induce increased hepatic or splenic BVR activity in rabbits. 5. Maximal BVR activities were attained using NADPH as cofactor at pH 8.7 in sheep and rabbits and at pH 8.4 in cattle. 6. Differing concentrations of bovine or human albumins enhanced or inhibited BVR activity quite differently in the various species. 7. The finding of a very low, but measurable BVR activity in lapine liver and spleen may explain, in part, why rabbits, unlike rats, cattle and sheep, excrete primarily biliverdin (70%) into bile.

Bilirubin excretion and bile flow in fed and fasted Brazilian squirrel monkeys (Saimiri sciureus)

Fasted Brazilian squirrel monkeys (BrSMs) exhibited slightly higher serum bilirubin levels (0.30 +/- 0.05 mg/dl) than others in the fed state (0.13 +/- 0.01). The mean liver weight was 50% lower following a 22 h fast. The rate of bile flow was unaffected by fasting and averaged 13.8 microliters/min/kg and 47.5 microliters/min/100g liver in six BrSMs. No significant difference in mean bilirubin excretion/min was observed on a body weight basis following fasting. When the mean rate of bilirubin excretion was calculated as a function of liver weight, a two-fold higher rate was present in fasted monkeys, but only at the p = 0.06 level of statistical significance. From data collected in this and earlier studies, it would appear that BrSMs represent the best animals studied to date to serve as experimental controls in comparative studies with Bolivian squirrel monkeys which exhibit a Gilbert-like syndrome.

Methemalbumin: Reality and Myth

The ability to form methemalbumin by binding oxidized heme is described frequently as a characteristic of albumin from all animal species. Actually, only albumin from a limited number of species makes methemalbumin. Lack of recognition of interspecies differences has led to the myth of methemalbumin in domestic animals. The literature on methemalbumin is reviewed including the chemical characteristics of true methemalbumin and the misuse of mythical methemalbumin.

DNA helicase II of Escherichia coli. Characterization of the single-stranded DNA-dependent NTPase and helicase activities

Escherichia coli helicase II has been purified to near homogeneity from cells harboring a multicopy plasmid containing the structural gene for helicase II, uvrD. In this paper a detailed description of the single-stranded DNA-dependent nucleoside 5'-triphosphatase and helicase reactions catalyzed by helicase II is presented. The results of this study suggest that nucleoside 5'-triphosphate hydrolysis provides the energy required for translocation of the enzyme along single-stranded DNA. Measurements of the rate of ATP hydrolysis using a variety of single-stranded DNAs of known structure and length suggest a processive translocation mechanism for helicase II. Single-stranded DNA coated with either Escherichia coli single-stranded DNA binding protein (SSB) or bacteriophage T4 gene 32 protein fails to support helicase II ATPase activity. Moreover, helicase II is apparently unable to displace a molecule of bound SSB protein from single-stranded DNA when it is encountered in the process of translocation along a single-stranded DNA effector. The helicase reaction has been characterized using an in vitro strand displacement helicase assay. The helicase reaction requires concomitant nucleoside 5'-triphosphatase hydrolysis that is satisfied by the hydrolysis of either rATP or dATP. As the length of duplex DNA present in the partial duplex helicase substrate is increased from 71 base pairs to 343 base pairs, the fraction of duplex DNA molecules that are unwound by helicase II decreases in the absence of any accessory proteins. However, the total number of base pairs of duplex DNA unwound depends primarily on the amount of enzyme added to the helicase reaction and not on the length of the duplex DNA present in the partial duplex DNA substrate. These data suggest the number of base pairs of duplex DNA unwound is directly proportional with the concentration of helicase II in the reaction mixture. In addition, the rate of the unwinding reaction is independent of the length of the duplex DNA available for unwinding. Helicase II has been shown to dissociate from single-stranded DNA molecules infrequently acting as an ATPase. However, the enzyme dissociates from partial duplex helicase substrates more frequently. This suggests a more distributive reaction mechanism on duplex DNA than was observed on single-stranded DNA substrates. The fraction of 343-base pair partial duplex DNA molecules unwound by helicase II can be increased by the addition of appropriate concentrations of E. coli SSB to the reaction. This suggests that helicase II and SSB may act in a concerted reaction to unwind duplex DNA.

Hematologic values in calves infected with Sarcocystis cruzi

Calves were inoculated with 2 X 10(5) Sarcocystis cruzi sporocysts. Red cell mass decreased dramatically between Days 21 and 35 post-infection and plasma volume increased concurrently, so that blood volume did not change significantly. Mild reticulocytosis and increased pyrimidine 5' nucleotidase activity in erythrocytes occurred between Days 35 and 42. Antiglobulin tests with anti-bovine IgG, IgM and C3 were negative, with the exception of a positive test for C3 in 1 of 6 infected calves.

Plasma-glucose concentrations in dogs and cats before and after surgery: comparison of healthy animals and animals with sepsis

Various surgical procedures were performed in healthy dogs and cats and in dogs and cats with sepsis. Plasma-glucose concentrations after surgery were usually increased over presurgical values. After surgery, cats had significantly higher plasma-glucose concentrations (P less than 0.05) than did dogs. Postsurgical concentrations for healthy dogs were between 100 to 200 mg/dl, whereas the concentrations for dogs with sepsis ranged from 66 to 356 mg/dl. Of 8 dogs with sepsis that developed postsurgical plasma-glucose concentrations of greater than 150 mg/dl, 4 (50%) died, whereas of 7 dogs with sepsis that developed postsurgical concentrations of less than 150 mg/dl, only 1 (14%) died; however, the difference between these 2 mortality percentages was not significant (P = 0.08).