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Biomedical subjects

Z Li

Publications and source records attributed to Z Li.

At least 1,081 records · Page 60Linked to original sources
PubMed1997

Involvement and identification of a lysine in the PPi-site of pyrophosphate-dependent phosphofructokinase from Giardia lamblia.

The substrate binding and/or catalytic site of the pyrophosphate-dependent phosphofructokinase (PPi-PFK) of Giardia lamblia was investigated using an ATP affinity label, 2',3'-dialdehyde of ATP, oxidized ATP (oATP), for the involvement of lysine residues. The enzyme, which uses PPi rather than ATP as a substrate was inhibited by low concentrations of oATP. Oxidized ATP behaves as an affinity label for the substrate binding site as evidenced by saturation kinetics with the formation of reversible complex prior to inactivation, and the observation that the inactivation was stoichiometric with the amount of oATP incorporated which extrapolated to 1 mol per mol of monomeric PPi-PFK. The critical lysine modified by oATP is proposed to be located at the PPi-binding site since complete protection is afforded by PPi; and under steady-state, PPi was competitive with the inhibitor. Other substrates of the reaction in either the forward or reverse direction did not completely protect against inactivation. This is further confirmed by the non-competitive inhibition displayed by either Pi or fructose 1,6, bisphosphate. Furthermore, the Km values for Pi and fructose 1,6 bisphosphate of the oATP-modified enzyme were not altered. The oATP-modified peptides were analyzed by HPLC peptide mapping, and the profile showed a major peak absorbing at 258 nm, which was absent when the modification was carried out in the presence of MgPPi. This peptide was sequenced and found to contain Lys-497. These results suggest that the essential lysine-497 modified by oATP is involved in the binding and/or catalysis of PPi and that an ATP-type of binding domain, with reference to the phosphoryl groups, is present in the PPi-dependent phosphofructokinase of Giardia.

Adenosine Triphosphate↗
PubMed1997

Agrin gene expression in mouse somatosensory cortical neurons during development in vivo and in cell culture.

Agrin is an extracellular matrix protein involved in the formation of the postsynaptic apparatus of the neuromuscular junction. In addition to spinal motor neurons, agrin is expressed by many other neuronal populations throughout the nervous system. Agrin's role outside of the neuromuscular junction, however, is poorly understood. Here we use the polymerase chain reaction to examine expression and alternative splicing of agrin in mouse somatosensory cortex during early postnatal development in vivo and in dissociated cell culture. Peak levels of agrin gene expression in developing cortex coincide with ingrowth of thalamic afferent fibres and formation of thalamocortical and intracortical synapses. Analysis of alternatively spliced agrin messenger RNA variants shows that greater than 95% of all agrin in developing and adult somatosensory cortex originates in neurons, including isoforms that have little or no activity in acetylcholine receptor aggregation assays. The levels of expression of "active" and "inactive" isoforms, however, are regulated during development. A similar pattern of agrin gene expression is also observed during a period when new synapses are being formed between somatosensory neurons growing in dissociated cell culture. Changes in agrin gene expression, observed both in vivo and in vitro, are consistent with a role for agrin in synapse formation in the central nervous system.

2-Amino-5-phosphonovalerate↗
PubMed1997

Commissioning of enhanced dynamic wedge on a ROCS RTP system.

The enhanced dynamic wedge (EDW) is clinically commissioned on a ROCS RTPS (Version 5.03) in a manner similar to that used for any standard physical wedge. The required data set for implementation includes central axis depth dose, and open and wedge beam profiles at several depths and output factors. The features distinguishing the EDW from the physical wedge are a sharp change in output with field size in the wedge plane and a primary intensity difference at the end of the wedge field because the moving jaw stops 0.5 cm short of the fixed jaw position for all field sizes, for safety reasons. The monitor unit (MU) calculation for an EDW field in ROCS is based on scaling factors that are derived from a normalized golden STT (NGSTT). This approach requires no change in the data file structure of ROCS. It was found that the output for EDW is very sensitive to the value of final moving jaw position. Every 0.5 cm difference between planned and set value can cause 3.5% error.

Radiotherapy Planning, Computer-Assisted↗
PubMed1997

Antitumor 8-chlorobenzocycloheptapyridines: a new class of selective, nonpeptidic, nonsulfhydryl inhibitors of ras farnesylation.

Ras farnesylation by farnesyl protein transferase (FPT) is an intracellular event that facilitates the membrane association of the ras protein and is involved in the signal transduction process. FPT inhibition could be a novel, noncytotoxic method of treating ras dependent tumor growth. We report here three structural classes of 8-chlorobenzocycloheptapyridines as novel, nonpeptidic, nonsulfhydryl FPT inhibitors having antitumor activity in mice when dosed orally. We discuss structural and conformational aspects of these compounds in relation to biological activities as well as a comparison to the conformation of a bound tetrapeptide FPT inhibitor.

Animals↗
PubMed1997

Polyamine derivatives as inhibitors of trypanothione reductase and assessment of their trypanocidal activities.

Trypanothione reductase (TR) occurs exclusively in trypanosomes and leishmania, which are the etiological agents of many diseases. TR plays a vital role in the antioxidant defenses of these parasites and inhibitors of TR have potential as antitrypanosomal agents. We describe the syntheses of several spermine and spermidine derivatives and the inhibiting effects of these compounds on T. cruzi TR. All of the inhibiting compounds displayed competitive inhibition of TR-mediated reduction of trypanothione disulfide. The three most effective compounds studied were N4,N8-bis(3-phenylpropyl)spermine (12), N4,N8-bis(2-naphthylmethyl)spermine (14), and N1,N8-bis(2-naphthylmethyl)spermidine (21), with Ki values of 3.5, 5.5 and 9.5 microM, respectively. Compounds 12, 14, and 21 were found to be potent trypanocides in vitro with IC50 values ranging from 0.19 to 0.83 microM against four T. brucei ssp. strains. However, these compounds did not prolong the lives of mice infected with trypanosomes. This work indicates that certain polyamine derivatives which target a unique pathway in Trypanosomatidae have potential as antitrypanosomal agents.

Animals↗
PubMed1997

Apoptosis signaling pathway in T cells is composed of ICE/Ced-3 family proteases and MAP kinase kinase 6b.

Fas/APO-1(CD95) ligation activates programmed cell death, a cellular process that plays an important role in the maturation of the host immune response. We show that activation of a specific MAP kinase kinase (MKK), MKK6b, is necessary and sufficient for Fas-induced apoptosis of Jurkat T cells. MKK6b activation occurs downstream of an interleukin-1 converting enzyme-like (ICE-like) protease(s), while execution of the apoptotic pathway by MKK6b requires both ICE- and CPP32-like proteases. Surprisingly, the p38 MAP kinase protein, a known substrate of MKK6b, does not participate in Fas/MKK6b-mediated apoptosis. These findings indicate a divergence of the MKK6b signaling pathways, one of which activates p38 and leads to regulation of gene expression, and one of which activates the ICE/Ced-3 family of proteases and leads to cell death. These studies represent a demonstration of an apoptotic pathway that is comprised of both the ICE/Ced-3 family of proteases and MAP kinase kinase 6.

Amino Acid Sequence↗
PubMed1997

The heating phenomenon produced by an ultrasonic fountain.

When a piece of plastic sheet is placed in the path of an ultrasonic fountain generated using a medical nebulizer in water, temperatures of up to 250 degrees C can be produced on the face of the sheet opposite the fountain impact. This paper describes the experimental methodology and results, and suggests that this phenomenon is the combined result of both the heating and mechanical effect of ultrasonic cavitation within the fountain.

Journal Article↗
PubMed1997

Desmin-lacZ transgene expression and regeneration within skeletal muscle transplants.

The purpose of this study was to investigate the initiation and time course of the regeneration process in fragments of skeletal muscle transplants as a function of muscle tissue age at implantation. The appearance of desmin occurs at the very beginning of myogenesis. The transgenic desmin nls lacZ mice used in the study bear a transgene in which the 1 kb DNA 5' regulatory sequence of the desmin gene is linked to a reporter gene coding for Escherichia coli beta-galactosidase. The desmin lacZ transgene labels muscle cells in which the desmin synthesis programme has commenced. We implanted pectoralis muscle fragments from fetal transgenic embryos and mature and old transgenic mice into mature non-transgenic mice. Early events of myogenesis occurring during regeneration started sooner in transplants from 4-month-old (day 3 post-implantation) muscle than in those from 24-month-old (day 5-6 post-implantation) muscle, and they lasted longer in those from young (day 17 post-implantation) than in those from old (day 14 post-implantation) muscle fragments. In adult muscle, transgene activation proceeded from the periphery toward the centre of the transplant. In transplants from fetal 18-day-old pectoralis, myotubes with transgene activity were observed from day 1 to day 19. Desmin immunoreactivity, which appeared about one day after transgene activation, was followed by myosin expression. In adult transplants, the continuity of laminin labelling was disrupted around degenerative fibres, illustrating alteration of the extracellular matrix. Our data suggest that satellite cells from old muscle tissue have lower proliferative capacity and/or less access to trophic substances released by the host (damaged fibres, vascularization) than those from fetal or young adult muscle.

Animals↗
PubMed1997

Alterations in sarcomere structure, collagen organization, mitochondrial activity, and protein metabolism in the avian low score normal muscle weakness.

Skeletal muscle fibers are surrounded by an extracellular matrix. The extracellular matrix is composed of glycoproteins, collagen, and proteoglycans. Proteoglycans have been suggested to play an important functional role in tissue differentiation. However, an understanding of how the extracellular matrix affects skeletal muscle development and function is largely unknown. In the avian genetic muscle weakness, low score normal (LSN), a late embryonic increase in the expression of decorin is followed by a subsequent increase in collagen crosslinking. The sarcomere organization, collagen fibril diameter and organization were investigated using transmission electron microscopy. Measurements were made at 20 days of embryonic development and 6 weeks posthatch. These studies showed changes in sarcomere organization and deterioration of muscle fibril structure in the LSN pectoral muscle. In vitro satellite cell cultures were developed and assayed for mitochondrial activity, and protein synthesis and degradation. In these analyses, mitochondrial activity from LSN satellite cells was significantly higher than those from normal pectoral muscle satellite cells. Protein synthesis rates between the normal and LSN satellite cell-derived myotubes were similar, but protein degradation rates were higher in the LSN cultures. Based on the reported functions of decorin as a regulator of cell proliferation and collagen fibril organization, it is possible that the late embryonic increase in decorin may be influencing the alterations in LSN sarcomere and collagen organization.

Animals↗
PubMed1997

Calcium signaling in transgenic mice overexpressing cardiac Na(+)-Ca2+ exchanger.

We have produced transgenic mice which overexpress cardiac Na(+)-Ca2+ exchange activity. Overexpression has been assessed by Western blot, Northern blot, and immunofluorescence. Functional overexpression was analyzed using membrane vesicles and isolated ventricular myocytes. In whole cell clamped myocytes dialyzed with 0.1-0.2 mM Fura-2, the magnitude of ICa and Ca2+i-transient triggered by ICa or caffeine were not significantly different in transgenic vs. control myocytes. In transgenic myocytes, activation of ICa, however, was followed by a large slowly inactivating transient inward current representing INa-Ca. This current depended on Ca2+ release as it was abolished when sarcoplasmic reticulum (SR) Ca2+ was depleted using thapsigargin. Cai-transients triggered by rapid application of 5 mM caffeine, even though equivalent in control and transgenic myocytes, activated larger INa-Ca (approximately 5 pA/pF at -90 mV) in transgenic vs. control myocytes (1.5 pA/pF). The decay rate of caffeine-induced Ca2+i-transient and INa-Ca was 2.5 times faster in transgenic than in control myocytes. 5 mM Ni2+ was equally effective in blocking INa-Ca in control or transgenic myocytes. In 9 out of 26 transgenic myocytes, but none of the controls, Ca2+ influx via the exchanger measured at +80 mV caused a slow rise in [Ca2+]i triggering rapid release of Ca2+ from the SR, SR Ca2+ release triggered by the exchanger at such potentials was accompanied by activation of transient current in the inward direction. In 2 mM Fura-2-dialyzed transgenic myocytes caffeine-triggered Cai-transients failed to activate INa-Ca even though the kinetics of inactivation of ICa slowed significantly in caffeine-treated myocytes. In 0.1 mM Fura-2-dialyzed transgenic myocytes 100 microM Cd2+ effectively blocked ICa and suppressed Cai-transients at -10 or +50 mV. Our data suggests that in myocytes overexpressing the exchanger, the content of intracellular Ca2+ pools and the signaling of its release by the Ca2+ channel vis-à-vis the Na(+)-Ca2+ exchanger were not significantly altered despite an up to ninefold increase in the exchanger activity. We conclude that the exchanger remains functionally excluded from the Ca2+ microdomains surrounding the DHP/ryanodine receptor complex.

Animals↗
PubMed1997

Identification of key gene products required for acquisition of plasmin-like enzymatic activity by group A streptococci.

Group A streptococci incubated in human plasma can acquire a plasmin-like enzymatic activity. This process involves at least two bacterial proteins and two human protein cofactors. In this study, the key bacterial proteins were identified by using a series of isogenic mutants of group A isolate, CS101. These studies confirm a key role for the secreted plasminogen activator, streptokinase, and identify the major surface fibrinogen-binding protein as the product of the mrp gene. The requirement for human fibrinogen and plasminogen as key cofactors was also confirmed.

Bacterial Proteins↗
PubMed1997

Epistasis for three grain yield components in rice (Oryza sativa L.).

The genetic basis for three grain yield components of rice, 1000 kernel weight (KW), grain number per panicle (GN), and grain weight per panicle (GWP), was investigated using restriction fragment length polymorphism markers and F4 progency testing from a cross between rice subspecies japonica (cultivar Lemont from USA) and indica (cv. Tequing from China). Following identification of 19 QTL affecting these traits, we investigated the role of epistasis in genetic control of these phenotypes. Among 63 markers distributed throughout the genome that appeared to be involved in 79 highly significant (P < 0.001) interactions, most (46 or 73%) did not appear to have "main" effects on the relevant traits, but influenced the trait(s) predominantly through interactions. These results indicate that epistasis is an important genetic basis for complex traits such as yield components, especially traits of low heritability such as GN and GWP. The identification of epistatic loci is an important step toward resolution of discrepancies between quantitative trait loci mapping and classical genetic dogma, contributes to better understanding of the persistence of quantitative genetic variation in populations, and impels reconsideration of optimal mapping methodology and marker-assisted breeding strategies for improvement of complex traits.

Adaptation, Physiological↗
PubMed1997

Genetics of hybrid sterility and hybrid breakdown in an intersubspecific rice (Oryza sativa L.) population.

F1 hybrid sterility and "hybrid breakdown" of F2 and later generations in rice (Oryza sativa L.) are common and genetically complicated. We used a restriction fragment length polymorphism linkage map and F4 progeny testing to investigate hybrid sterility and hybrid breakdown in a cross between "widely compatible" O. sativa ssp. japonica cultivar Lemont from the Southern U.S. and ssp. indica cultivar Teqing from China. Our results implicate different genetic mechanisms in hybrid sterility and hybrid breakdown, respectively. Hybrid sterility appeared to be due to recombination within a number of putative differentiated "supergenes" in the rice genome, which may reflect cryptic structural rearrangements. The cytoplasmic genome had a large effect on fertility of both male and female gametes in the F1 hybrids. There appeared to be a pair of complementary genes that behaved like "wide compatibility" genes. This pair of genes and the "gamete eliminator" (S1) or "egg killer" (S-5) may influence the phenotypic effects of presumed supergenes in hybrids. Hybrid breakdown appeared to be largely due to incompatibilities between indica and japonica alleles at many unlinked epistatic loci in the genome. These proposed mechanisms may partly account for the complicated nature of postreproductive barriers in rice.

Chromosome Mapping↗
PubMed1997

Epimerization studies of LSD using 1H nuclear magnetic resonance (NMR) spectroscopy.

A study was conducted to determine the conditions needed to achieve the equilibrium concentration for the epimerization of d-lysergic acid diethylamide (LSD) to iso-LSD. The reaction was followed by integration of the C-9 resonance of LSD and iso-LSD by proton nuclear magnetic resonance (NMR). The C-9 resonance of LSD and iso-LSD appear as singlets at 6.35 and 6.27 ppm respectively. Starting with pure LSD, the conversion to iso-LSD is attained at temperatures above 37 degrees C and pH levels over 7.0. At a pH of 7.0 or higher, the LSD/iso-LSD ratio of 9:1 is achieved after one week at 45 degrees C or two weeks at 37 degrees C. Starting with iso-LSD, the conversion to LSD requires more vigorous conditions. The 9:1 LSD/iso-LSD ratio is attained only after 6 weeks at a temperature of 45 degrees C and a pH of 9.7. At lower pH levels, the reaction proceeds more slowly. The 9:1 LSD/iso-LSD ratio is achieved whether the starting material is LSD or iso-LSD and therefore represents an equilibrium concentration (K = 9). In addition, the more vigorous conditions needed to achieve equilibrium of iso-LSD to LSD demonstrate the difficulty in extraction of the epimerizable proton of iso-LSD. This study is the first to quantitate the epimerization of LSD by NMR techniques and establishes the conditions needed to induce epimerization in solution.

Drug Stability↗
PubMed1997

Transitions in health care use and expenditures among frail older adults by payor/provider type.

OBJECTIVES: To assess whether transitions in health care expenditures differed over time by payor/provider type: Medicare fee-for-service (FFS), Medicaid-Medicare, and Medicare HMO. DESIGN: Longitudinal study. SETTING: A large, nonprofit healthcare system in San Diego, California. PARTICIPANTS: A total of 450 frail older people who responded to the baseline and follow-up surveys and who survived the 18-month study period. MEASUREMENTS: Measures included three total expenditure categories for each 6-month period: low users (< $4000); medium users ($4000-$19,999); or high users ($20,000+). Seven conceptually meaningful expenditure trajectories over time were identified: (1) consistently low expenditures, (2) consistently medium expenditures, (3) consistently high expenditures, (4) decreasing expenditures, (5) increasing expenditures, (6) U-shaped expenditures, and (7) inverted U-shaped expenditures. MAIN RESULTS: Logistic regression analyses showed that HMO enrollees were about twice as likely as Medicaid-Medicare beneficiaries to have consistently low expenditures, but no differences were found between the FFS and HMO groups on this trajectory. Other expenditure patterns showed no significant differences by payor/provider group. Significant interactions among payor/provider type, low/medium/ high expenditure status, and time were observed for inpatient hospital care, skilled nursing/rehabilitation care, and home health care. CONCLUSION: This study illustrates the complexity of frail older people with respect to their health care expenditures and service use. Expanded efforts to control health care expenditures for frail older people should focus first on those who are dually-enrolled. In addition, because mean medical expenditures for high users enrolled in different payor/ provider groups were surprisingly similar, the data suggest that containing expenditures for individuals in the highest usage group ($20,000+) presents challenges for physicians practicing in an era of healthcare reform, regardless of payor/ provider setting.

Aged↗
PubMed1997

Interactions between biofilms and the environment.

The surfaces of bacteria are highly interactive with their environment. Whether the bacterium is Gram-negative or Gram-positive, most surfaces are charged at neutral pH because of the ionization of the reactive chemical groups which stud them. Since prokaryotes have a high surface area-to-volume ratio, this can have surprising ramifications. For example, many bacteria can concentrate dilute environmental metals on their surfaces and initiate the development of fine-grained minerals. In natural environments, it is not unusual to find such bacteria closely associated with the minerals which they have helped develop. Bacteria can be free-living (planktonic), but in most natural ecosystems they prefer to grow on interfaces as biofilms; supposedly to take advantage of the nutrient concentrative effect of the interface, although there must also be gained some protective value against predators and toxic agents. Using a Pseudomonas aeruginosa model system, we have determined that lipopolysaccharide is important in the initial attachment of this Gram-negative bacterium to interfaces and that this surface moiety subtly changes during biofilm formation. Using this same model system, we have also discovered that there is a natural tendency for Gram-negative bacteria to concentrate and package periplasmic components into membrane vesicles which bleb-off the surface. Since some of these components (e.g., peptidoglycan hydrolases) can degrade other surrounding cells, the vesicles could be predatory; i.e., a natural system by which neighboring bacteria are targeted and lysed, thereby liberating additional nutrients to the microbial community. This obviously would be of benefit to vesicle-producing bacteria living in biofilms containing mixed microbial populations.

Biofilms↗
PubMed1997

Neuropathogenesis of chimeric simian/human immunodeficiency virus infection in pig-tailed and rhesus macaques.

We recently reported that a chimeric simian/human immunodeficiency virus (SHIVKU-1) developed in our laboratory caused progressive depletion of CD4+ T lymphocytes and AIDS within 6 months of inoculation into pig-tailed macaques (M. nemestrina). None of the pig-tailed macaques showed productive SHIV infection in the central nervous system (CNS). In this report, we show that by further passage of the pathogenic virus in rhesus macaques [M. mulatta], we have derived a new strain of SHIV (SHIVKU-2) that has caused AIDS and productive CNS infection in 3 of 5 rhesus macaques infected with the virus. Productive replication of SHIV in the CNS was clearly shown by high infectivity titers and p27 protein levels in brain homogenates, and in 2 of the 3 rhesus macaques this was associated with disseminated, nodular, demyelinating lesions, including focal multinucleated giant cell reaction, largely confined to the white matter. These findings were reminiscent of HIV-1 associated neurological disease, and our immunohistochemical and in situ hybridization data indicated that the neuropathological lesions were associated with the presence of SHIV-specific viral antigens and nucleic acid respectively. However, the concomitant reactivation of opportunistic infections in these macaques suggested that such pathogens may have influenced the replication of SHIV in the CNS, or modified the neuropathological sequelae of SHIV infection in the rhesus species, but not in pig-tailed macaques. Our findings in the two species of macaques highlight the complexities of lentiviral neuropathogenesis, the precise mechanisms of which are still elusive.

Acquired Immunodeficiency Syndrome↗