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Biomedical subjects

A Kaplan

Publications and source records attributed to A Kaplan.

At least 163 records · Page 9Linked to original sources
PubMed1980

Acid hydrolases from Dictyostelium discoideum contain phosphomannosyl recognition markers.

Acid hydrolases from mammalian sources contain phosphorylated oligosaccharides which function as recognition markers for their receptor-mediated endocytosis by human fibroblasts. The discovery that glycopeptides derived from the slime mold, Dictyostelium discoideum, contain mannose 6-phosphate led to the suggestion that acid hydrolases from this source might also bear the marker. To test this hypothesis, the binding and endocytosis of purified beta-D-glucosidase (EC 3.2.1.21), beta-N-acetyl-D-hexosaminidase (EC 3.2.1.52), and alpha-D-mannosidase (EC 3.2.1.24) by human fibroblasts were investigated. These enzymes underwent endocytosis with efficiencies of 8.6 to 60%/mg/h, and 1 mM mannose 6-phosphate markedly inhibited their uptake (80 to 100%). The specificity of inhibition by sugar phosphates, the saturation kinetics of endocytosis, and the binding properties of D. discoideum acid hydrolases were similar to those reported for enzyme preparations derived from mammalian sources. In addition, 95 to 100% of the beta-D-glucosidase or alpha-D-mannosidase molecules from D. discoideum preparations were competent for in vitro clearance. Furthermore, the three purified acid hydrolases contain 5 to 7 mol of mannose 6-phosphate/mol of enzyme. This indicates that, unlike many mammalian enzyme preparations, most if not all of these enzyme molecules from D. discoideum contain the phosphomannosyl recognition marker.

Dictyostelium↗
PubMed1980

Salt-Induced Metabolic Changes in Dunaliella salina.

An increase of medium NaCl concentration induces Dunaliella cells to evolve O(2) photosynthetically even in the absence of CO(2). This NaCl-induced O(2) evolution may reflect the induced conversion of reserve carbohydrate to glycerol. The quantum yield for the NaCl-induced O(2) evolution, in the absence of CO(2), is 1.5-fold higher than that obtained for CO(2) fixation. Since the synthesis of glycerol from reserve carbohydrate in the absence of CO(2) requires only 0.5 ATP/NADPH, whereas photosynthesis requires at least 1.3 ATP/NADPH, it is concluded that the ATP/2e(-) ratio coupled to NADP reduction in Dunaliella is lower than required for CO(2) fixation.

Journal Article↗
PubMed1980

Internal Inorganic Carbon Pool of Chlamydomonas reinhardtii: EVIDENCE FOR A CARBON DIOXIDE-CONCENTRATING MECHANISM.

The external inorganic carbon pool (CO(2) + HCO(3) (-)) was measured in both high and low CO(2)-grown cells of Chlamydomonas reinhardtii, using a silicone oil layer centrifugal filtering technique. The average internal pH values were measured for each cell type using [(14)C]dimethyloxazolidinedione, and the internal inorganic carbon pools were recalculated on a free CO(2) basis. These measurements indicated that low CO(2)-grown cells were able to concentrate CO(2) up to 40-fold in relation to the external medium. Low and high CO(2)-grown cells differed in their photosynthetic affinity for external CO(2). These differences could be most readily explained as being due to the relative CO(2)-concentrating capacity of each cell type. This physiological adaptation appeared to be based on changes in the abilities of the cells actively to accumulate inorganic carbon using an energy-dependent transport system.The energy dependence of CO(2) accumulation was investigated, using the inhibitors methyl viologen, 3-(3,4-dichlorophenyl)-1,1 dimethylurea, carbonyl cyanide trifluoromethoxyphenylhydrazone, and 3,5-di-tert-butyl-4-hydroxybenzylide nemalononitrile. It appears that the concentrating mechanism in both cell types may be dependent upon an energy supply linked to both phosphorylation in general and photophosphorylation. The treatment of low CO(2)-grown cells with the carbonic anhydrase inhibitor ethoxyzolamide decreased the apparent photosynthetic affinity for CO(2). This was correlated with a decrease in the transport of inorganic carbon into the cells.The nature of the CO(2)-concentrating mechanism, particularly with respect to a bicarbonate transport system, is discussed, and its possible occurrence in other algae is assessed.

Journal Article↗
PubMed1978

Receptor-mediated uptake of lysosomal enzymes.

This paper reviews the evidence for two different forms of carbohydrate-mediated recognition of lysosomal enzymes by cell surface receptors. The recognition marker on lysosomal enzymes which are rapidly pinocytosed by fibroblasts contains phosphate, probably linked to D-mannose as a phosphomannosyl moiety. The fraction of lysosomal hydrolases bearing this recognition marker for fibroblasts varies, depending on the tissue source. Another form of recognition accounts for rapid plasma clearance of infused lysosomal enzymes in the rat. This rapid clearance is mediated by receptors on Kupffer cells and other reticuloendothelial cells that recognize mannosyl residues on the glycoprotein hydrolases.

Animals↗
PubMed1977

Purification and properties of a triacylglycerol lipase from Mycobacterium phlei.

In order to study the metabolism of triacylglycerol in mycobacteria, an intracellular particulate triacylglycerol lipase (EC 3.1.1.3) was purified 800-fold from stationary phase cells of Mycobacterium phlei. Extraction of whole cell suspensions with 5% Triton X-100, followed by ion-exchange chromatography of the extract on two successive DEAE-cellulose columns produced a preparation which was nearly homogeneous by the criterion of analytical isoelectric focusing in acrylamide gels (one band, pI. 3.8) and by polyacrylamide gel electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis resolved the preparation into six protein bands. Lipase activity stable to electrophoresis in sodium dodecyl sulfate was extracted from the 40 000 molecular weight region of the gels. ith phosphate or maleate buffer the enzyme exhibits a broad pH optimum around 6.0 with sigmoid saturation kinetics (Hill number 2), and an apparent Km of 8.8 mM for tripalmitoylglycerol. Citrate and other carboxylic acids increase the apparent V up to 3-fold with the Hill number approaching 1.0. In a series of p-nitrophenyl esters tested (C2-C18), p-nitrophenylmyristate was hydrolyzed most rapidly. The saturation curve for p=nitrophenylmyristate was sigmoid and unaffected by citrate. The role of this activity in the metabolism of triacylglycerols by Mycobacteria is discussed.

Anions↗
PubMed1977

Immunotherapy with autologous white cell infusions ("lymphocytes") in the treatment of recurrrent glioblastoma multiforme: a preliminary report.

Autologous leukocytes (10(7) to 10(9)), obtained with the Haemonetic's Leukaphoresis apparatus, were inoculated directly into recurrent glioblastoma tumors via indwelling catheters or by direct intratumoral injection through existing craniotomy openings. The rational use for autologous leukocyte (lymphocyte) infusions was based on in vitro autologous lymphocyte cytotoxicity to glioblastoma cells in the absence of serum inhibitory factors. Seven of 17 patients treated had life expectancy under 1 month; all patients had received definitive surgery, and all but two received radiation, nitrosourea chemotherapy and/or dexamethasone, and showed evidence of clinically recurrent disease. Following autologous leukocyte infusion (lymphocyte/granulocyte ratio 1:1), eight patients sustained clinical improvement and were alive up to 17 months later. No neurotoxicity ascribable to the procedure has been observed. One patient, who was comatose at the time of single leukocyte infusion, returned to full activity and lived for 17 months without an increase in tumor mass by brain scan. These results suggest that infusions of autologous leukocytes (lymphocyte-monocytes) directly into glioblastoma may be a viable additional treatment for glioblastoma and certainly warrants further evaluation.

Adult↗
PubMed1977

Phosphohexosyl components of a lysosomal enzyme are recognized by pinocytosis receptors on human fibroblasts.

Human beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC 3.2.1.31), like many other glycoprotein lysosomal hydrolases, is specifically taken up from the culture medium by human fibroblasts. Prior work has indicated that the enzyme exhibits charge heterogeneity and that "high-uptake" forms, i.e., those rapidly internalized by human fibroblasts, are more acidic than slowly internalized forms. Here we present two lines of evidence that the acidic group required for the high-uptake property of certain forms of the enzyme is a phosphate on, or in proximity to, a D-mannose-type carbohydrate. The first line of evidence was obtained from analysis of inhibition of enzyme pinocytosis by yeast mannans, phosphorylated sugars, and sugars. Mannans that contained phosphate were more potent inhibitors than those that did not contain phosphate. D-Mannose 6-phosphate was a more potent inhibitor than either D-mannose 1 phosphate or 2-deoxy-D-glucose 6-phosphate. D-Mannose and certain related sugars were weak pinocytosis inhibitors, while 2- and 4-epimers of mannose were noninhibitory. Competitive inhibition was demonstrated and the apparent Kis estimated for the following compounds: Saccharomyces cerevisiae mannan from mutant X2180-mnnl, 3 X 10(-6) M; mannan from wild-type S. cerebisiae, 3 X 10(-5) M; D-mannose 6-phosphate, 6 X 10(-5) M; L-fucose, 4 X 10(-2) M; and D-mannose, 6 X 10(-2) M. The second line of evidence comes from the observation that alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] treatment of human platelet beta-glucuronidase abolished its "high-uptake" activity, without diminishing its catalytic activity, and converted some forms of the heterogeneous enzyme to less acidic forms.

Alkaline Phosphatase↗
PubMed1977

Phosphohexosyl recognition is a general characteristic of pinocytosis of lysosomal glycosidases by human fibroblasts.

We recently presented data showing that mannose-6-phosphate was a potent competitive inhibitor of pinocytosis of human platelet beta-glucuronidase, and that treatment of "high-uptake" forms of the enzyme with alkaline phosphatase destroyed the high-uptake property of the enzyme without diminishing its catalytic activity. These data indicate that phosphate is a necessary component of the recognition marker on the enzyme for pinocytosis by human fibroblasts, and suggest that the phosphate on high-uptake forms of the enzyme is present as a phosphohexosyl moiety. Results presented here show that mannose-6-phosphate is also a potent inhibitor of pinocytosis of the following enzyme preparations: (a) beta-glucuronidase from human spleen, liver, placenta, and urine; (b) beta-hexosaminidase and beta-galactosidase from human platelets; (c) beta-hexosaminidase from human fibroblast secretions. Alkaline phosphatase treatment of all these enzymes except beta-galactosidase, which was unstable to the incubation conditions and could not be tested, greatly diminished the uptake activity of the enzymes without diminishing their catalytic activity. These results suggest that phosphohexosyl recognition is a general characteristic of pinocytosis of lysosomal glycosidases.

Alkaline Phosphatase↗
PubMed1976

Four-phase study of computer-assisted and slide-tape methods of stimulating clinical endodontic problems.

1. Computer-assisted instruction of stimulated clinical endodontic problems is superior to a slide-tape presentation for test selection but not for diagnosis and treatment planning. 2. The lack of a difference in diagnosis is likely due to the already superior performance of students in diagnosis at the University of Kentucky without computer assistance. A study with students of less background might reveal a difference in presentation methods. 3. Students with high GPSs score higher on a written test of endodontic clinical judgment. 4. Reliable results on the effects of a human tutor's supplementing machine instruction were not obtained. 5. Students felt that the problems presented in this study were useful in preparing for clinical treatment of patients. 6. After some exposure to machine methods of instruction, students divided into three sizable groups, one preferring a human teacher, another preferring a machine, and the third having no preference. The decision to use only machine or human instruction cannot then be made from student attitudes. 7. Students liked the active participation and immediate responses of the computer but not the time necessary to complete the problems. 8. Students liked the self-pacing, speed, and convenience of the slide-tape method but not the incompleteness of the problems presented by this method. 9. It appears that there is some justification from this study for offering both slide-tape and computer-assisted presentations to students.

Attitude↗
PubMed1975

Hereditary progressive atrioventricular conduction defect.

New data on genetics, including an extensive pedigree and certain aspects of natural history, have been compiled on Family S, which is characterized by a hereditary progressive atrioventricular (A-V) conduction defect. Concordance analysis of heart block in affected parents and their offspring suggests as a working hypothesis transmission of diathesis for the defect by means of a Mendelian autosomal dominant factor. Regression of the defect in several relatives, including reversion from first degree heart block to normal A-V conduction, defies explanation at this time. However, rapport established with the unusually large (1,067 members) and cooperative kindred will permit longitudinal evaluation of these findings.

Adolescent↗
PubMed1975

Evolution of sleep spindles in childhood.

Twenty-six normal children (age range range 4-68 months) were studied during Stage 2 sleep which occurred within 20 min preceding or following the first three REM periods of the night. Sleep spindles were measured in Fp1T3. The number, length, and percent of sleep spindle activity were found to be maximal at 46 months of age. Beyond 6 months spindle activity decreased to reach minimal values by 27 months, remained fairly constant to 54 months, then rose again to higher values in the oldest subjects. The mean spindle-wave frequency was 1314 c/sec in subjects younger than 40 months, but was 12-13 c/sec in older subjects. Spindle onsets in Fp1T3 and Fp2T4 were more often concurrent in older as compared to younger subjects. Auditory stimulation (binaural clicks, 60 dB above hearing threshold) affected neither the incidence nor the length of spindles during sleep. Because sizable changes in sleep spindle activity are found between 3 months and 5 years of age, and because such changes are relatively consistent between subjects, it is concluded that sleep spindles recorded between frontal and temporal areas may serve as a useful index of neural maturation in the human subject.

Acoustic Stimulation↗