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Biomedical subjects

A Kaplan

Publications and source records attributed to A Kaplan.

At least 109 records · Page 6Linked to original sources
PubMed1992

Phenotypic Complementation of High CO(2)-Requiring Mutants of the Cyanobacterium Synechococcus sp. Strain PCC 7942 by Inosine 5'-Monophosphate.

The high CO(2)-requiring mutants of Synechococcus PCC 7942, D4 and R14, were obtained by deletion or inactivation (respectively) of an open reading frame immediately downstream of rbc (the operon encoding the subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase). These mutants exhibit photosynthetic characteristics similar to those of high CO(2)-grown wild type, unlike other cyanobacterial high CO(2)-requiring mutants, where the apparent photosynthetic affinity for inorganic carbon is approximately 2 orders of magnitude lower than that of the wild type. Sequence analysis and metabolic complementation of the mutants by inosine 5'-monophosphate identified this open reading frame as the cyanobacterial equivalent of purK, the eubacterial gene encoding subunit II of phosphoribosyl aminoimidazole carboxylase in the purine biosynthetic pathway. Exposure of high CO(2)-grown Synechococcus to low CO(2) conditions led to the induction of transcription of purK. It is suggested that the high CO(2)-requiring phenotype of these mutants resulted from the defect in purine biosynthesis after exposure to low CO(2). We also raise the possibility that the level of cellular purines is involved in the process of adaptation of cyanobacteria to low concentrations of CO(2).

Journal Article↗
PubMed1991

Physiological and molecular aspects of the inorganic carbon-concentrating mechanism in cyanobacteria.

This paper reviews progress made in elucidating the inorganic carbon concentrating mechanism in cyanobacteria at the physiological and molecular levels. Emphasis is placed on the mechanism of inorganic carbon transport, physiological and genetical analysis of high-CO(2)-requiring mutants, the polypeptides induced during adaptation to low CO(2), the functional significance of carboxysomes, and the role of carbonic anhydrase. We also make occasional reference to the green algal inorganic carbon-concentrating mechanism.

Journal Article↗
PubMed1991

Alcohol and other drugs: the response of the political and medical institutions.

Formal and informal social control in shaping individual behaviors toward the use of alcohol and other drugs is discussed. Emphasis is placed on formal social control as it occurs in two major institutions. The state, which embodies the political and legal structures of the society is discussed in terms of the social control of some of the consequences of drinking, such as public drunkenness, alcoholism, operating vehicles with specific blood alcohol levels, and crime and alcohol use. The medical institution's involvement in alcohol and drug control is discussed in terms of the physician's role in diagnosing alcohol and drug dependent individuals. Two contemporary cases, those of pregnant addicts and alcohol-related organ transplant patients, illustrate the significant interactions between the responses of the political and medical institutions, and the broader influences that help shape these responses.

Alcoholism↗
PubMed1990

Methaemoglobinaemia due to accidental sodium nitrite poisoning. Report of 10 cases.

Nitrates and nitrites are widely used in the food and chemical industry. Poisoning with these agents may be potentially life-threatening as a result of the production of methaemoglobin. A group of 10 patients suffering from moderate to severe methaemoglobinaemia after accidental intoxication with a sodium nitrite salt is described. One patient died but the other 9 recovered rapidly. The low mortality rate was attributed to prompt diagnosis and institution of appropriate therapy with methylene blue and ascorbic acid.

Adult↗
PubMed1989

Characteristics of the sulfation of N-linked oligosaccharides in vesicles from Dictyostelium discoideum: in vitro sulfation of lysosomal enzymes.

Lysosomal enzymes from Dictyostelium discoideum contain unusual sulfated N-linked oligosaccharides, whose synthesis has been well studied in vivo. However, little is known about the properties of the pertinent sulfotransferases. To study these transferases, we have prepared a cell-free system which transfers 35SO4 from 3'-phosphoadenosine 5'-phosphosulfate to either endogenous or exogenous acceptors. We found that the 35SO4 was released from macromolecules by protein N-glycanase F to yield a mixture of anionic oligosaccharides with 1-6 negative charges. Some of the labeled molecules contained acid-stable methyl phosphodiesters but none contained phosphomoesters or acid-labile diesters. The sulfate was found in molecules with the acid stability characteristic of esters of primary alcohols. In all these ways, the products resembled those generated in vivo. We also demonstrated that a membrane-associated form of beta-hexosaminidase and the precursor of alpha-mannosidase were among the products. In addition, glycoproteins prepared from a sulfation-deficient mutant strain could act as exogenous acceptors in permeabilized vesicles.

Chromatography, Ion Exchange↗
PubMed1989

Nature of the light-induced h efflux and na uptake in cyanobacteria.

We investigated the nature of the light-induced, sodium-dependent acidification of the medium and the uptake of sodium by Synechococcus. The rate of acidification (net H(+) efflux) was strongly and specifically stimulated by sodium. The rates of acidification and sodium uptake were strongly affected by the pH of the medium; the optimal pH for both processes being in the alkaline pH range. Net proton efflux was severely inhibited by inhibitors of adenosine triphosphatase activity, energy transfer, and photosynthetic electron transport, but was not affected by the presence of inorganic carbon (C(i)). Light and C(i) stimulated the uptake of sodium, but the stimulation by C(i) was observed only when C(i) was present at the time sodium was provided. Amiloride, a potent inhibitor of Na(+)/H(+) antiport and Na(+) channels, stimulated the rate of acidification but inhibited the rate of sodium uptake. It is suggested that acidification might stem from the activity of a light dependent proton excreting adenosine triphosphatase, while sodium transport seems to be mediated by both Na(+)/H(+) antiport and Na(+) uniport.

Journal Article↗
PubMed1989

The 5'-flanking region of the gene encoding the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase is crucial for growth of the cyanobacterium Synechococcus sp. strain PCC 7942 at the level of CO2 in air.

Transformation of the high-CO2-requiring mutants (hcr) O221 and E1 derived from the cyanobacterium Synechococcus sp. strain PCC 7942 by a wild-type DNA library restored their ability to grow at the level of CO2 in air. A plasmid (pE12) containing a 10-kilobase DNA insert was rescued from a O221 heterogenote and proved to transform both O221 and E1 to the wild-type phenotype. The capacity of the pE12 subclones to confer the wild-type phenotype to O221 transformants enabled the mapping of the mutation in O221 (designated hcrO221) within a 232-base-pair PstI-BstXI DNA restriction fragment. Sequence analysis revealed two open reading frames (ORFs) at positions -1745 to -1262 (ORFI) and -1218 to -393 (ORFII) upstream of the rbcL gene. A 3-kilobase PstI fragment of O221 was cloned, and hcrO221 was found to be a point mutation within the PstI-BstXI region -1309 nucleotides upstream of the rbcL gene. The significance of this flanking region for adaptation to air levels of CO2 was further demonstrated by the generation of new hcr mutants following insertional inactivation of wild-type DNA in the BstXI site. Electron microscopy revealed aberrant carboxysome structures in growing cells of the hcr mutants, a defect that was possibly related to the mutation, since transformation with pE12 derivatives restored the carboxysome structure to normal.

Air↗
PubMed1988

Molecular cloning of the cDNA which encodes beta-N-acetylhexosaminidase A from Dictyostelium discoideum. Complete amino acid sequence and homology with the human enzyme.

beta-N-Acetylhexosaminidase A (EC 3.2.1.52), the product of the nag A gene, is a lysosomal enzyme which is developmentally regulated in Dictyostelium discoideum. The enzyme plays a role during the slug stage of development in the maintenance of pseudoplasmodia of normal size. We used a homogeneous preparation of deglycosylated enzyme subunits to generate antibody. The antibody was suitable for screening a lambda gt11 cDNA expression library derived from the mRNA of late log stage axenic cells. We isolated seven positive clones. One of these contains the complete coding sequence of the protein. We also isolated a genomic clone which contains 800 base pairs of 5'-flanking sequence and 728 base pairs of coding sequence. Analysis of the sequences and of primer extension studies indicates an inferred transcript size of 1665 bases which closely matches the 1.8-kilobase mRNA size estimated by Northern blot analysis of poly(A+) mRNA from the organism. The sequence contains an open reading frame which encodes a protein of 59,787 kDa. This equals the apparent molecular weight in sodium dodecyl sulfate-polyacrylamide gels of in vitro translated enzyme. The amino terminus of the purified enzyme appeared to be blocked, but internal peptide sequences were obtained by automated Edman degradation of gel-purified peptides generated by treatment of protein subunits with staphylococcal V-8 protease. These sequences are included in the inferred sequence. In addition to a typical signal sequence, the open reading frame encodes a second candidate transmembrane region, a serine-rich region, and four potential N-glycosylation sites. These are discussed with regard to the localization and processing of the enzyme during its biogenesis. Beginning at amino acid 100 of the Dictyostelium enzyme sequence, 36% of its amino acids are identical to the corresponding sequence of the beta chain, and 33% are identical with those of the alpha chain of human beta-N-acetylhexosaminidase. This is strong evidence that the Dictyostelium enzyme is homologous to the alpha and beta chains of the human enzyme.

Amino Acid Sequence↗
PubMed1988

Corynebacterium aquaticum infection in a patient with chronic granulomatous disease.

Patients with chronic granulomatous disease are uniquely susceptible to infection with catalase-producing bacteria. Staphylococcus aureus, Klebsiella, Escherichia coli and Serratia marcescans are common infecting organisms. A 17-month-old boy with Corynebacterium aquaticum bacteremia is reported. This is only the third documented infection with this non-JK diphtheroid and the first case infection in a patient with chronic granulomatous disease. It is likely that our patient's underlying immune defect predisposed him to infection with this unusual, catalase-producing organism. Although these bacteria are common contaminants and rarely infecting agents, true infection should be considered in patients with chronic granulomatous disease from whom a diphtheroid is isolated.

Corynebacterium↗
PubMed1988

Is there a role for the 42 kilodalton polypeptide in inorganic carbon uptake by cyanobacteria?

Cyanobacterial cells accumulate substantial amounts of a membrane-associated 42 kilodalton polypeptide during adaptation to low CO(2) conditions. The role of this polypeptide in the process of adaptation and in particular in the large increase in the ability to accumulate inorganic carbon (C(i)), which accompanies this process, is not yet understood. We have isolated a mutant Synechococcus PCC7942 that does not accumulate the 42 kilodalton polypeptide. The mutant requires a high-CO(2) concentration for growth and exhibits a very low apparent photosynthetic affinity for extracellular C(i). The latter might be attributable to the observed defective ability of the mutant to utilize the intracellular C(i) pool for photosynthesis. The 42 kilodalton polypeptide does not appear to participate directly in the active transport of C(i), since the difference between the observed capabilities for CO(2) and HCO(3) (-) uptake of the mutant and the wild type is not sufficient to account for their different growth and photosynthetic performance. Furthermore, high CO(2)-grown wild-type cells, where we could not detect the 42 kilodalton polypeptide, transported CO(2) faster than the mutant. An analysis of the curves relating the rate of accumulation of C(i) to the concentration of CO(2) or HCO(3) (-) supplied, in the presence or absence of carbonic anhydrase, indicated that under the experimental conditions used here, CO(2) was the preferred C(i) species taken up by Synechococcus.

Journal Article↗
PubMed1987

The Stoichiometry between CO(2) and H Fluxes Involved in the Transport of Inorganic Carbon in Cyanobacteria.

The pH of the medium during CO(2) uptake into the intracellular inorganic carbon (C(i)) pool of a high CO(2)-requiring mutant (E(1)) and wild type of Anacystis nidulans R2 was measured. Experiments were performed under conditions where photosynthetic CO(2) fixation is inhibited. There was an acidification of the medium during CO(2) uptake in the light and an alkalization during CO(2) efflux after darkening. A one to one stoichiometry existed between the amounts of H(+) appearing in the medium and CO(2) taken up into the intracellular C(i) pool, regardless of the carbon species transported. The results indicate that (a) CO(2) is taken up simultaneously with an efflux of equimolar H(+), probably produced as a result of CO(2) hydration during transport and (b) HCO(3) (-) produced by hydration of CO(2) in the medium was transported into the cells without accompanying net flux of H(+) or OH(-). The influx and efflux of C(i) during C(i) transport produced nonequilibrium between CO(2) and HCO(3) (-) in the medium, with the concentration of HCO(3) (-) being higher than that expected under equilibrium conditions. The nonequilibrium was present even under the conditions where the influx of C(i) is compensated by its efflux. The direction of this nonequilibrium suggested that efflux of HCO(3) (-) occurs during uptake of C(i).

Journal Article↗