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Biomedical subjects

K Roberts

Publications and source records attributed to K Roberts.

At least 199 records · Page 11Linked to original sources
PubMed1975

Red cell surface structure. Stabilization by cholesterol sulfate as evidenced by scanning electron microscopy.

Scanning electron microscopic studies demonstrate that the normal biconcave shape of the human erythrocyte is maintained in hypotonic saline when physiological levels (10 minus 5M) of cholesterol sulfate are added to the solutions. Cholesterol sulfate is a naturally occurring sterol conjugate in plasma and erythrocyte membranes and we propose that it may belong to that class of amphipathic molecules responsible for the maintenance of structure of the erythrocyte by interaction with membrane components.

Cell Membrane↗
PubMed1968

Microbiology of saturated salt solutions and other harsh environments. IV. New observations on ribonucleotide-induced recovery of KCl-habituated Penicillium notatum.

Salt-tolerant mutant Penicillium notatum sub-cultured in a glucose-peptone broth saturated with KCl shows continued attenuated growth when transferred to salt-free broth. Additional tests have shown E. coli S-RNA to be inferior to yeast RNA preparations, that base-free phosphate sources are inactive, but that nicotinamide adenine dinucleotide and flavine adenine dinucleotide are moderately active. All phosphate derivatives of adenine, cytosine and guanosine and inosine were active including 5'-polyphosphates, 3'(2')-monophosphates 5'-monophosphates, and adenine 3', 5'-cyclic monophosphate. Uracil derivatives were of low activity at best. Among base precursors, orotic acid was moderately active whereas imidazoles were not. The high activity of inosine 5'-phosphate a precursor of other purine nucleotides suggested that one mode of KCl action might involve a block in conversion of 4-amino-5-imidazole carboxamide ribonucleoside to the hypoxanthine nucleotide.

Nucleotides↗
PubMed1967

Living relative of the microfossil Kakabekia.

A living, ammonia-obligate, umbellate form, similar to the Precambrian microfossil Kakabekia umbellata Barghoorn, has been isolated from two soil specimens collected at Harlech, Wales. This organism is amenable to culture on agar and in broth. The two soil specimens are similar in that they differ from a typical clay loam in high content of carbon, hydrogen, and organic nitrogen and low levels of sodium, potassium, and titanium. In all other constituents, such as calcium, magnesium, and iron, they are quite dissimilar. Kakabekia-like forms can be grown in glucose-anmonia media with the latter as the sole source of nitrogen, but they can also be grown on peptone and silicate in glucose-free media. Ammonia is necessary, and growth is always slow without glucose. The fission process was not observed, but the enlargement and differentiation of a preumbellate structure into its "mature" form, followed by disintegration (senescence) of this stage, was seem. An ontogeny is proposed in which the stalk and basal bulb of the complete umbellate structure are assumed to be part of the reproductive appartus.

Ammonia↗
PubMed1967

Effects of metabolic poisons on rice: the comparative sensitivity of aerobic and anaerobic modes of germination.

Rice germinates equally well when incubated in air and in nitrogen. It was therefore chosen for a comparative study of the effect of oxygen status in a single organism upon the activity of conventional metabolic poisons. Inhibitor activity was based upon the concentration required for 50% inhibition of germination. The inhibitors were: AgNO(3), HgCl(2), phenylmercuric acetate, iodoacetamide, KCN, NaN(3), NaF, fluoroacetate, 2,4-dinitrophenol, Na(2)HAsO(4) and CO. Only 5 inhibitors out of 11 differed significantly in their effects on aerobic and anaerobic germination. These included phenylmercuric acetate (N(2)), sodium fluoroacetate (air), NaN(3) (air), and 2,4-dinitrophenol (N(2)). CO activity was manifest only in air and it was photo-reversible. The effects of CO, NaN(3), and fluoroacetate were consistent with their conventional role in aerobic metabolism. The failure of KCN to discriminate was attributed to its relative non-specificity. 2,4-Dinitrophenol behaved anomalously, requiring a 20-fold lower concentration for inhibition under nitrogen than under air. Among sulfhydryl poisons, only phenylmercuric acetate differentiated between germination in air and nitrogen and was nearly 8 times more active under nitrogen. Uptake measurements using phenylmercuric acetate and arsenate showed both compounds to be in greater concentration under aerobic conditions, thereby rendering unlikely any explanation based upon greater permeability under nitrogen. In addition to other anomalies, the fact that NaN(3), fluoroacetate and CO inhibited anaerobic germination at any concentration requires explanation. It was concluded that the general significance and utility of metabolic inhibitor studies in vivo required further evaluation.

Journal Article↗
PubMed1967

Microbiology of saturated salt solutions and other harsh environments. II. Ribonucleotide dependency in the growth of a salt-habituated Penicillium notatum in salt-free nutrient media.

A strain of Penicillium notatum has been found growing upon media containing saturated calcium acetate which upon passage through media containing saturated KC1 loses its ability to grow at normal rates in salt-free glucose-peptone medium. This salt-habituated form can be restored to a near-normal growth rate by adding yeast extract, RNA or RNA-hydrolysates, but not by DNA or its hydrolysate. The 4 RNA nucleotides in combination replace yeast extract whereas riboside and base combinations do not. Adenylic, guanylic or cytidilic acids, singly or in various combinations, are even more effective, but uridylic acid alone is not active at all. Ribonucleotide pairs including uridylic acid are less active, but 3 ribonucleotide combinations are highly effective, even in the presence of uridylic acid. Differential effects were evident in mycelial form and sporulation, as well as growth. In addition to a direct role in Penicillium RNA metabolism, the significance of ribonucleotides in energy metabolism or cell wall synthesis is mentioned as alternatives to explain their restorative effects.

Culture Media↗