PubMed Health⌕ Search

Biomedical subjects

A E Palmer

Publications and source records attributed to A E Palmer.

At least 19 recordsLinked to original sources
PubMed2001

Decay of the peroxide intermediate in laccase: reductive cleavage of the O-O bond.

Laccase is a multicopper oxidase that contains four Cu ions, one type 1, one type 2, and a coupled binuclear type 3 Cu pair. The type 2 and type 3 centers form a trinuclear Cu cluster that is the active site for O(2) reduction to H(2)O. To examine the reaction between the type 2/type 3 trinuclear cluster and dioxygen, the type 1 Cu was removed and replaced with Hg(2+), producing the T1Hg derivative. When reduced T1Hg laccase is reacted with dioxygen, a peroxide intermediate (P) is formed. The present study examines the kinetics and mechanism of formation and decay of P in T1HgLc. The formation of P was found to be independent of pH and did not involve a kinetic solvent isotope effect, indicating that no proton is involved in the rate-determining step of formation of P. Alternatively, pH and isotope studies on the decay of P revealed that a proton enhances the rate of decay by 10-fold at low pH. This process shows an inverse k(H)/k(D) kinetic solvent isotope effect and involves protonation of a nearby residue that assists in catalysis, rather than direct protonation of the peroxide. Decay of P also involves a significant oxygen isotope effect (k(16)O(2)/k(18)O(2)) of 1.11 +/- 0.05, indicating that reductive cleavage of the O-O bond is the rate-determining step in the decay of P. The activation energy for this process was found to be approximately 9.0 kcal/mol. The exceptionally slow rate of decay of P is explained by the fact that this process involves a 1e(-) reductive cleavage of the O-O bond and there is a large Franck-Condon barrier associated with this process. Alternatively, the 2e(-) reductive cleavage of the O-O bond has a much larger driving force which minimizes this barrier and accelerates the rate of this reaction by approximately 10(7) in the native enzyme. This large difference in rate for the 2e(-) versus 1e(-) process supports a molecular mechanism for multicopper oxidases in which O(2) is reduced to H(2)O in two 2e(-) steps.

Hydrolysis↗
PubMed2001

Spectroscopy and reactivity of the type 1 copper site in Fet3p from Saccharomyces cerevisiae: correlation of structure with reactivity in the multicopper oxidases.

Fet3p is a multicopper oxidase recently isolated from the yeast, Saccharomyces cerevisiae. Fet3p is functionally homologous to ceruloplasmin (Cp) in that both are ferroxidases. However, by sequence homology Fet3p is more similar to fungal laccase, and both contain a type 1 Cu site that lacks the axial methionine ligand present in the functional type 1 sites of Cp. To determine the contribution of the electronic structure of the type 1 Cu site of Fet3p to the ferroxidase mechanism, we have examined the absorption, circular dichroism, magnetic circular dichroism, electron paramagnetic resonance, and resonance Raman spectra of wild-type Fet3p and type 1 and type 2 Cu-depleted mutants. The spectroscopic features of the type 1 Cu site of Fet3p are nearly identical to those of fungal laccase, indicating a very similar three-coordinate geometry. We have also examined the reactivity of the type 1 Cu site by means of redox titrations and stopped-flow kinetics. From poised potential redox titrations, the E degrees of the type 1 Cu site is 427 mV, which is low for a three-coordinate type 1 Cu site. The kinetics of reduction of the type 1 Cu sites of four different multicopper oxidases with two different substrates were compared. The type 1 site of a plant laccase (Rhus vernicifera) is reduced moderately slowly by both Fe(II) and a bulky organic substrate, 1,4-hydroquinone (with 6 equiv of substrate, k(obs) = 0.029 and 0.013 s(-)(1), respectively). On the other hand, the type 1 site of a fungal laccase (Coprinus cinereus) is reduced very rapidly by both substrates (k(obs) > 23 s(-)(1)). In contrast, both Fet3p and Cp are rapidly reduced by Fe(II) (k(obs) > 23 s(-)(1)), but only very slowly by 1,4-hydroquinone (10- and 100-fold more slowly than plant laccase, respectively). Semiclassical theory is used to analyze the origin of these differences in reactivity in terms of type 1 Cu site accessibility to specific substrates.

Ceruloplasmin↗
PubMed1999

Targeted mutations in a Trametes villosa laccase. Axial perturbations of the T1 copper.

Trametes villosa laccase was mutated on a tetrapeptide segment near the type 1 site. The mutations F463M and F463L were at the position corresponding to the type 1 copper axial methionine (M517) ligand in Zucchini ascorbate oxidase. The mutations E460S and A461E were near the T1 copper site. The mutated Trametes laccases were expressed in an Aspergillus oryzae host and characterized. The E460S mutation failed to produce a transformant with meaningful expression. The F463L and A461E mutations did not significantly alter the molecular and enzymological properties of the laccase. In contrast, the F463M mutation resulted in a type 1 copper site with an EPR signal intermediate between that of the wild type laccase and plastocyanin, an altered UV-visible spectrum, and a decreased redox potential (by 0.1 V). In oxidizing phenolic substrate, the mutation led to a more basic optimal pH as well as an increase in kcat and Km. These effects are attributed to a significant perturbation of the T1 copper center caused by the coordination of the axial methionine (M463) ligand.

Base Sequence↗
PubMed1998

Site-directed mutations in fungal laccase: effect on redox potential, activity and pH profile.

A Myceliophthora thermophila laccase and a Rhizoctonia solani laccase were mutated on a pentapeptide segment believed to be near the type-1 Cu site. The mutation L513F in Myceliophthora laccase and the mutation L470F in Rhizoctonia laccase took place at a position corresponding to the type-1 Cu axial methionine (M517) ligand in Zucchini ascorbate oxidase. The triple mutations V509L,S510E,G511A in Myceliophthora laccase and L466V,E467S,A468G in Rhizoctonia laccase involved a sequence segment whose homologue in ascorbate oxidase is flanked by the M517 and a type-1 Cu-ligating histidine (H512). The single mutation did not yield significant changes in the enzymic properties (including any significant increase in the redox potential of the type-1 Cu). In contrast, the triple mutation resulted in several significant changes. In comparison with the wild type, the Rhizoctonia and Myceliophthora laccase triple mutants had a phenol-oxidase activity whose pH optimum shifted 1 unit lower and higher, respectively. Although the redox potentials were not significantly altered, the Km, kcat and fluoride inhibition of the laccases were greatly changed by the mutations. The observed effects are interpreted as possible mutation-induced structural perturbations on the molecular recognition between the reducing substrate and laccase and on the electron transfer from the substrate to the type-1 Cu centre.

Amino Acid Sequence↗
PubMed1993

Infiltrating angiolipoma of skeletal muscle. Transplacental induction in nonhuman primates by N-nitrosoethylurea.

BACKGROUND: In humans, relatively little is known on the association of prenatal exposure to cancer-causing agents and the development of specific tumors later in life as a consequence. Therefore, the effects on the offspring of carcinogen exposure during gestation and the development of tumors later in life were studied in nonhuman primates. EXPERIMENTAL DESIGN: Pregnancy was confirmed in Erythrocebus patas (patas) and Macaca mulatta (rhesus) by palpation at 27 to 40 days of gestation. Pregnant animals were treated once weekly intravenously from that time with N-nitrosoethylurea according to different dosing regimens for 6 to 19 weeks with 0.05 to 0.2 mmol/kg/injection. RESULTS: A common lesion developing in only the offspring of mothers treated early in pregnancy was identical with the human condition referred to as intramuscular angioma, hemangioma, or infiltrating angiolipoma of skeletal muscle. In the rhesus, one of 7 animals, and in the patas, 18 of 78 monkeys developed these processes (10 to 40% per group). The lesions typically arose within, infiltrated and displaced skeletal muscle. They occurred most commonly in the lower extremities, followed by the upper extremities and the head; they recurred in three cases of incomplete resection but did not metastasize. The tumors were seen mainly in young adults of both sexes (latency range: 4 to 76 months) and consisted of vessels of variable caliber, and to varying degrees, mature adipose and connective tissue, undifferentiated mesenchymal cells, and lymphoid cell aggregates. Ultrastructurally, the endothelium possessed numerous Weibel-Palade bodies and showed strong immunoreactivity for von Willebrand factor by immunohistochemistry and immunoelectron microscopy. CONCLUSIONS: The present investigation suggests a classification of these lesions as infiltrating angiolipoma of skeletal muscle originating from a pluripotent mesenchymal stem cell, caused by exposure to carcinogens during early pregnancy. The great clinical and morphologic similarity of this condition with that observed in humans suggests that it may likewise be caused by exposure to an agent during pregnancy.

Animals↗
PubMed1990

Interspecies scaling of the pharmacokinetics of N-nitrosodimethylamine.

The pharmacokinetics of N-nitrosodimethylamine was studied in patas monkeys following i.v. doses of 0.5, 1.0, and 5.0 mg/kg and a p.o. dose of 1.0 mg/kg, and in Swiss mice at i.v. doses of 1.0 and 2.0 mg/kg. In the patas monkey the pharmacokinetics was linear over the i.v. dose range studied. The mean clearance (Cl), steady-state volume of distribution (Vss), mean residence time, and elimination half-life (t 1/2) were 103.3 +/- 26.7 (SD) ml/min, 3061 +/- 821 ml, 30.8 +/- 10.8 min, and 21.1 +/- 8.5 min, respectively. Assuming that the pharmacokinetics was linear at the p.o. dose used, the p.o. bioavailability of N-nitrosodimethylamine in the monkey was 49%. The pharmacokinetics was also linear in mice, and the average Cl, Vss, mean residence time, and t 1/2 were 3.81 ml/min, 21.0 ml, 5.5 min, and 11.9 min, respectively. These data and data for rats, hamsters, rabbits, dogs, and pigs taken from the literature were used to scale Cl and Vss to body weight using the allometric equation. The resulting equation for Cl was Cl = 49.7B0.998 and the equation for Vss was Vss = 748B1.05 where B is body weight in kg. The fit of the data to the equation was excellent in both cases. Using these equations and assuming a body weight of 70 kg for humans, the Cl and Vss for N-nitrosodimethylamine in humans are estimated to be 3450 ml/min and 64,800 ml, respectively.

Animals↗
PubMed1988

Isolation and partial characterization of the low-molecular-mass zinc/cadmium-binding protein from the testes of the patas monkey (Erythrocebus patas). Distinction from metallothionein.

The mammalian testes are generally quite susceptible to cadmium. A deficiency of metallothionein (MT), a metal-binding protein linked to Cd tolerance, has been observed in rat testes and may explain the sensitivity in rats. Little is known about the metal-binding proteins in primate testes. Thus this study examined the nature of these proteins in a non-human primate species, the patas monkey (Erythrocebus patas). In all cases proteins isolated from testes were compared with authentic MT isolated from the liver of a zinc-treated monkey. A low-molecular-mass Zn/Cd-binding protein was seen in testicular and hepatic cytosol after gel filtration. Neither protein had substantial amounts of associated copper. These proteins could be partially purified from both sources by heat treatment and acetone precipitation. When such extracts were further separated by reverse-phase h.p.l.c., four hepatic forms were isolated, all of which proved to be authentic MT by amino acid analysis. However, only two testicular forms were separated by h.p.l.c., both of which had amino acid compositions quite unlike that of MT, having a much lower cysteine content and amino acids which are absent from MT (leucine and phenylalanine). The testicular protein appeared to be uninducible by Zn treatment. These results suggest that the low-molecular-mass Cd/Zn-binding proteins in the patas testes are not MTs and further support the hypothesis that a MT deficiency may be an important determinate of the marked testicular sensitivity to Cd toxicity.

Amino Acids↗
PubMed1987

B virus, Herpesvirus simiae: historical perspective.

Between 1932 and 1972, 24 known infections of man by B virus caused 23 cases of encephalitis and 18 fatalities. The virus has been isolated from dermal lesions and neural ganglia from macaque monkeys. Serological evidence of infection is complicated by close antigenic relationships between B virus, Herpesvirus simplex, and SA8. Hyperimmune globulin produced from monkey, horse, and rabbit sera has not proved highly effective. Formalin-inactivated vaccine appears safe and antigenic in man but has not been licensed. Half of all human subjects have neutralizing B virus antibody related to their H. simplex titer. More stable animal populations and the improved use of protective apparel have reduced, but not eliminated, the risk of B virus to man.

Animals↗
PubMed1986

Differences among isolates of simian hemorrhagic fever (SHF) virus.

Simian hemorrhagic fever (SHF) virus is a member of the Togaviridae family which currently is unclassified to genus. We have studied the relatedness of four different SHF virus isolates obtained from infected macaque or patas monkeys. Differences were found among isolates in type and severity of disease produced in patas monkeys, cell sensitivity to infection, viral antigens, and levels of specific antibody induced in patas monkeys. Based on these criteria, the four isolates have been grouped in two categories: those producing acute infections in patas monkeys (LVR, P-180) and those producing persistent infections (P-248, P-741). The P-180 isolate induced the most severe disease in experimentally infected patas monkeys, but only occasionally were their infections fatal. Persistently infected patas monkeys were viremic over a period of years, but showed no signs or symptoms of infection. All four isolates were found to be antigenically related by use of enzyme-linked immunosorbent assay (ELISA); the P-248 isolate showing the weakest antigenic relationship. However, none of the four isolates induced cross-neutralizing antibodies in infected patas monkeys. High titers of specific IgG antibody (up to 31,250 as determined by ELISA) were induced in acutely infected patas monkeys (LVR, P-180), but antibody was barely detectable (less than or equal to 50) in persistently infected patas monkeys (P-248, P-741). LVR lytically infected USU-104 cells, patas monkey peritoneal macrophages (PMAC), and rhesus monkey PMAC. The P-180 isolate lytically infected both patas monkey PMAC and rhesus monkey PMAC, but not USU-104 cells. The isolates producing persistent infections (P-248, P-741) lytically infected only rhesus monkey PMAC. These results show that marked differences exist among isolates of SHF virus from naturally infected animals. These differences should be useful in categorizing new isolates.

Animals↗
PubMed1986

Elimination of persistent simian hemorrhagic fever (SHF) virus infection in patas monkeys.

Devastating epizootics of simian hemorrhagic fever (SHF) have been iatrogenically initiated in captive colonies of macaque monkeys by strains of SHF virus emanating from asymptomatic persistently infected patas monkeys. We have found that persistently infected patas monkeys can be cleared of their infection by superinfection with strains of SHF virus which cause acute infections in this species. All 20 persistently infected animals subjected to this procedure have been cleared of their infection within 3 months. These animals were shown to be virus free by the most sensitive in vitro and in vivo tests currently available and periodic tests of serum from these animals over several years have shown them to remain virus free. Superinfection has in some cases caused some adverse clinical symptoms (anorexia, lethargy, facial edema, dehydration, and mild subcutaneous hemorrhages), but with supportive care, no fatal infections have occurred. Thus, superinfection with acute strains of SHF virus is a highly effective method of eliminating persistent infection in patas monkeys.

Animals↗
PubMed1985

Endocrine profile of pregnancy in the patas monkey (Erythrocebus patas).

Spontaneous toxemia occurs in approximately 6% of pregnancies in patas monkeys (Erythrocebus patas). To assess further the relevance of this animal as a model system for toxemia of pregnancy in humans, we characterized the endocrine profile of the patas pregnancy by analyzing weekly blood samples for estrone, estradiol, estriol, progesterone, aldosterone, and PRA throughout gestation. The profiles obtained bear striking resemblance to those described for human pregnancy, an unexpected finding since the patas monkey is not a higher hominoid. We conclude that the patas monkey may provide a model of toxemia relevant to study of the human disorder and is superior to other animal models which require surgical manipulation and are characterized by secondary hyperreninemia.

Aldosterone↗
PubMed1985

N-Nitroso-N-methylurea initiation in multiple tissues for organ-specific tumor promotion in rats by phenobarbital.

Effects of phenobarbital [(PB) CAS: 50-06-6], a systemic tumor promoter, on carcinogenesis initiated by the broad-spectrum carcinogen N-nitroso-N-methylurea [(NMU) CAS: 684-93-5] were investigated in F344/NCr rats. Single and divided doses of NMU were evaluated for this purpose in 4-week-old rats of both sexes. Rats received iv injections of either 0.2 mmol NMU/kg (body wt) once or 0.05 mmol NMU/kg (body wt) for 4 weeks (1 injection/wk), followed by or concurrently with PB (0.05% in drinking water) that was continued until the termination of the experiment. Half the rats were killed at 52 weeks and survivors at 80 weeks. At 52 weeks, PB given subsequent to NMU or concurrently with divided doses of NMU significantly enhanced the incidence of thyroid follicular tumors only in male rats. This sex difference in thyroid tumorigenesis was somewhat less pronounced in animals killed at 80 weeks. Only 1 liver cell adenoma occurred in males and none in females given NMU alone. PB given concurrently with divided doses of NMU enhanced the yield of hepatocellular foci/cm2 but had no significant effect on hepatic tumor development. Subsequent exposure to PB, however, significantly promoted hepatocarcinogenesis in rats of both sexes given NMU in divided doses; 50% of males and 40% of females given NMU (0.05 mmol/kg, administered four times) followed by PB had hepatocellular adenomas and carcinomas by 80 weeks. PB did not affect the incidence of any other kind of neoplasms seen in NMU-initiated or control rats. These lesions included squamous cell neoplasms of the skin, oropharynx, and forestomach; nonsquamous epithelial tumors of mammary gland, pituitary body, intestinal mucosa, and urinary bladder; tumors of the central and peripheral nervous system; and mesenchymal tumors of the kidney. A sequence of multiple low doses of NMU appeared to be a convenient and useful systemic, multitissue, tumor-initiation regimen for systematic investigation of organ-specific tumor promotion in rats.

Animals↗
PubMed1982

Teratological effects of western equine encephalitis virus on the fetal nervous system of Macaca mulatta.

Fetal rhesus monkeys were inoculated intracerebrally with an attenuated strain of western equine encephalitis virus. All animals developed microcephaly. Twelve of sixteen monkeys developed ex vacuo hydrocephalus. All virus inoculated fetuses developed WEE virus antibody. Virus could not be recovered at the time of delivery. Monkeys with the highest WEE antibody titers showed the greatest degree of hydrocephalus.

Animals↗
PubMed1981

Betamethasone and the rhesus fetus: effect on lung morphometry and connective tissue.

Pregnant rhesus monkeys (Macaca mulatta) at 67 to 85% of term pregnancy were treated with betamethasone for 3 days and then delivered by cesarean section. These treated fetuses had larger lung volumes (32.6 +/- 1.8 ml/kg of body weight) compared to gestational age-matched controls (22.9 +/- 3.2 ml/kg of body weight; P less than 0.025) but no alterations in surfactant properties as measured by amniotic fluid L/S ratios, alveolar deflation stability, or lung phosphatidylcholine. These findings suggest that betamethasone effects an increase in fetal lung volume by some method other than alteration in alveolar surfactant concentrations. Results also demonstrated an 11% increase in the collagen to elastin concentration in the treated fetuses as compared to the control animals (P less than 0.01), suggesting alterations in lung connective tissue. Morphometric studies done on the air-fixed inflated lung demonstrated a decrease in the number of alveoli per unit volume of lung among the treated animals (0.95 +/- 0.07 x 10(6)) compared to the control animals (1.19 +/- 0.08 x 10(6); P less than 0.025) and a reduction in the mean surface area of the lungs of the treated animals (506 +/- 10 cm2 per cm3) compared to the control animals (561 +/- 9 cm2 per cm3; P less than 0.005). These findings suggest that at least part of the increased maximal lung volumes is related to increased alveolar distensibility. Together, these pressure volume findings, biochemical studies, and morphometric analyses indicate that a major effect of betamethasone on the rhesus fetal lung is to alter lung connective tissue characteristics. Alterations in lung surfactant appear to be of less functional significance in this rhesus fetal model. The disparity between these findings and other animal studies might be due to differences in species, the preparation, or the method of glucocorticoid administration.

Animals↗
PubMed1981

Pathology of gestational choriocarcinoma induced in patas monkeys by ethylnitrosourea given during pregnancy.

A rapidly fatal neoplastic disease with histological and clinical features resembling gestational choriocarcinoma in humans has been observed in patas monkeys. Timed pregnant females were given ethylnitrosourea (ENU) intravenously at doses of 0.1 to 0.4 mmol/kg body weight, beginning on day 30 of gestation and continuing weekly for a total of 12 injections. Of 59 monkeys given ENU during pregnancy, four of 12 subjected to the highest dose and three of the remaining 47 given lower doses died of choriocarcinoma within six months of cessation of ENU exposure. Death was usually caused by exsanguinating haemorrhage. At necropsy, tumour deposits were always numerous in the lungs and were frequently observed in abdominal viscera. An obvious primary uterine tumour was never found, and only one small primary was detected grossly. Sub-endometrial masses of tumour cells were generally observed microscopically, invading the endometrial stroma and forming endovascular tumour deposits in the veins. Both uterine and extrauterine tumour deposits were highly haemorrhagic, often partially necrotic, and consisted of cytotrophoblast-like cells with frequent mitoses, a high degree of cellular pleomorphism and variable but often prominent cytoplasmic glycogen. This tumour was never seen in males or non-gravid adult females. Chorionic gonadotrophin assays conventionally used for human and macaque samples were negative in both normally pregnant and tumour-bearing patas, and did not contribute to the diagnosis. Trophoblast of patas monkeys appears highly susceptible to the carcinogenic effects of ENU and provides an animal model for gestational choriocarcinoma.

Animals↗
PubMed1981

Penicillin treatment for group B streptococcal meningitis in the rhesus monkey.

Penicillin therapy for experimentally produced neonatal meningitis due to intracerebral inoculation of group B streptococci (GBS) was studied in 25 rhesus monkeys. Penicillin was administered either therapeutically to the newborns 3 hours after GBS inoculation or prophylactically as a bolus to the pregnant females 2 hours before delivery. The neonatal mortality in the newborn treatment groups was 40% (6 of 15) compared to 100% (5 of 5) in the maternal prophylaxis group, and 0% (0 of 5) among uninfected and untreated controls. It was concluded that although penicillin can be used successfully to treat neonates with meningitis after intracerebral inoculation of GBS, penicillin given antepartum as bolus prophylaxis to the mother monkey was ineffective.

Animals↗
PubMed1981

Vaginal adenosis in Cebus apella Monkeys exposed to DES in utero.

Vaginal adenosis comparable to that seen in DES-exposed human newborns exposed to diethylstilbestrol (DES) was observed in 4 (100%) female Cebus apella monkey neonates exposed to DES in utero. Columnar Epithelium lined the vaginal canal and deep crypts in the underlying stroma. The ectocervix was markedly papillary and covered with columnar epithelium that was continuous with the endocervical epithelium. By comparison, the vagina of unexposed newborn and juvenile cebus monkeys up to 15 months of age was filled with a solid core of squamous cells that also covered the cervix and extended into the endocervix. Vaginal adenosis has been produced in mice by neonatal treatment with DES. The mouse model, however, excludes the fetoplacental unit. The cebus monkey provides a model for the investigation of teratogenic effects of intrauterine exposure to DES.

Animals↗