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Biomedical subjects

N Miller

Publications and source records attributed to N Miller.

At least 217 records · Page 12Linked to original sources
PubMed1975

The activation of phospholipase C from Clostridium Welchii by quinine: an absolute requirement for calcium ions.

Quinine activates the hydrolysis of phosphatidyl choline suspensions by phospholipase C (E.C. 3.1.4.3) obtained from Clostridium welchii. Low levels of calcium are an absolute requirement for this activation: Mg2+, Ba2+, Sr2+, and Zn2+ are ineffective. The induction period, or lag phase for this enzyme is dependent upon both calcium concentration and substrate interfacial surface area. At low concentrations (less then 50 muM) calcium ions affect the induction period but not the maximal rate of hydrolysis, whereas guinine predominantly affects the rate of hydrolysis by alterations in the surface charge carried by the substrate.

Calcium↗
PubMed1975

Malaria, quinine and red cell lysis.

An hypothesis is presented to explain the red cell lysis which accompanies an acute malarial infection, as well as the mode of action of certain schizonticidal drugs in the quinoline and acridine series. Quinine and a number of other antimalarial drugs have been found to counteract the inhibition by protein of fatty acid-induced lysis, when tested in an in vitro system. It is suggested that these schizonticides exert their chemotherapeutic effect by inducing the premature lysis of the parasitized red cell, as a result of relieving the inhibition by protein of haemolysis.

Binding, Competitive↗
PubMed1975

Effect of volatile fatty acids on water and ion absorption from the goat colon.

The absorption of volatile fatty acids (VFA) and the influence of VFA on the net transport of inorganic electrolytes and water were examined in the temporarily isolated colon of the conscious goat. Perfusion of the colon with a solution similar in content to that normally present in the cecal outflow showed that the net absorption of VFA was more rapid than that of any other ion present in the solution. When the VFA were replaced with Cl, the net absorption of Na and water was reduced nearly twofold. Increasing the pH of the solution from 6.0 to 7.4 in the presence of VFA also resulted in a twofold decreased in the net transport of Na and water. Perfusion of the colon with a hypertonic solution resulted in approximately zero net water transport; however, the net absorption of Na and VFA continued at similar rates as before. These results support the concept that the colon primarily conserves solute followed by the passive movement of water. They also demonstrate that VFA are rapidly absorbed from the goat colon and indicate a striking influence of VFA on the net transport of Na and water. The presence of VFA in the large intestine may be important for normal absorptive function.

Animals↗
PubMed1975

Evolutionary nature of human reverse transcriptase and of viral-related DNA synthesized in vitro by human leukemic cells.

The reverse transcriptase and endogenous DNA product synthesized by virus-like particles in the cytoplasm of human leukemic cells have been studied for their genetic relatedness to homologous components obtained from several animal RNA tumor viruses. The human reverse transcriptase activity was inhibited by antibodies prepared against reverse transcriptase from some animal RNA tumor viruses. The DNA molecules synthesized endogenously by the human cytoplasmic particle in the presence of actinomycin D, using the reverse transcriptase enzyme and RNA template residing in the particle, hybridized to 70S RNA purified from certain animal RNA tumor viruses. Both the human reverse transcriptase and DNA product are closely related to homologues from primate type-C viruses, more distantly related to those from murine type-C viruses, and essentially unrelated to similar structures from feline or avian type-C viruses. They are not related to type-B RNA tumor viruses. The results demonstrate that the components from the human leukemic cells are viral (type-C) and primate in nature.

Cytoplasm↗
PubMed1975

Pituitary gonadotropin response to luteinizing hormone-releasing hormone (LH-RH) in males with azo- and oligospermia.

Twenty-one males with azo- or oligospermia presenting with infertility and with no evidence of organic disease were studied with luteinizing hormone - releasing hormone (LH-RH). A pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) response was present in all cases and was normal in the majority of the subjects. Serum testosterone and 17 beta estradiol levels were normal in all cases studied. No significant correlations were found between the gonadotropin estimations and sperm count, basal serum testosterone or testosterone response to human chorionic gonadotropin. It is concluded that LH-RH is of limited diagnostic use in the investigation of this group of patients with male infertility and provides no further insight into the pathogenesis of this condition.

Adult↗
PubMed1970

Photohydration of uridine in the RNA of coliphage R17. II. The relationship between ultraviolet inactivation and uridine photohydration.

Uridine photohydrates (6-hydroxy-5,6-dihydrouridine) are the major products formed upon irradiation of the RNA bacteriophage R17 with ultraviolet light at 280 mmu, while cyclobutane-type pyrimidine dimerization does not occur to an appreciable extent. The suppression of dimerization may indicate that the RNA inside the phage is held in a rigid conformation in close contact with the phage protein. A value of 0.94 (+/-0.10) uridine photohydrates per biological hit is obtained from a correlation of the fraction of phage surviving with the number of photohydrates formed as a function of ultraviolet dose. It is concluded that uridine photohydrates represent a major part of the lethal damage caused by ultraviolet light in bacteriophage R17. An efficient system for dark repair of uridine photohydration seems to be lacking in E. coli.

Coliphages↗
PubMed1969

Photohydration of uridine in the RNA of coliphage R17. I. Reductive assay for uridine photohydration.

Photohydration of uridine in the RNA of E. coli bacteriophage R17 has been investigated with the help of a new chemical method which avoids digestion of the irradiated polymer. The uridine photohydrates are reductively cleaved with sodium borotritiide and the radioactively labeled fragment, 1,3-propane-diol-(3)H(alpha), (3)H(alpha), (3)H(gamma), formed in this reaction is isolated and used as a measure for the extent of uridine photohydration in the irradiated RNA. The influence of the conformational state of R17-RNA on the cross section of uridine photohydration (sigma(H)) was investigated. The cross section for irradiation at 280 mmu at 25 degrees was largest in 6 M urea (sigma(H) = 0.053), slightly smaller in low salt (<10(-3)M Na(+); sigma(H) = 0.050), and substantially smaller in 0.15 M Na(+) (sigma(H) = 0.038). The closeness of the values for sigma(H) in urea and low salt indicates that a majority of the uridine residues in R17-RNA in the low salt medium at 25 degrees are not hydrogen bonded and destacked. The significant suppression of photohydration in 0.15 M Na(+) on the other hand shows that a substantial portion of the uridine residues in R17-RNA are participating in base pairing and base stacking under these conditions. Our results demonstrate that studies of uridine photohydration may, beyond their importance to photobiology, yield information specifically about the conformational state of the uridine-rich regions of a RNA, information which cannot be readily obtained by other techniques.

Coliphages↗