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Biomedical subjects

J Roberts

Publications and source records attributed to J Roberts.

At least 631 records · Page 35Linked to original sources
PubMed1976

General practice observed. Child abuse and general practice.

In a general practice of 9250 patients with 1841 children under 10 there were 12 cases of actual abuse during 1973-6. In March 1976 30 children were at risk. A preventive scheme was set up and the short-term outcome was good. There were no cases of serious abuse among the children at risk.

Child Abuse↗
PubMed1976

Purification and properties of a highly potent antitumor glutaminase-asparaginase from Pseudomonas 7Z.

Crystalline glutaminase-asparaginase which is effective against solid as well as ascites tumors was prepared from soil isolate organism Pseudomonas 7A. This enzyme has a ration of Vmax for L-glutamine and L-asparagine of 2.0. The presence of glutamic acid in the growth medium is essential for optimal enzyme production and glucose inhibits the production of glutaminase-asparaginase. The purification procedure provides an overall yield of 40 to 45% from crude cell extract to homogeneous glutaminase-asparaginase and is adaptable to large scale production of the enzyme. The specific activity of homogeneous enzyme is 160 +/- 15 i.u./mg of protein and the E1% 280 is 9.8. No disulfide or sulfhydryl groups appear to be present on the enzyme. The isoelectric point of glutaminase-asparaginase by isoelectric focusing on ampholine polyacrylamide gel plates is 5.8. The Km values for L-glutamine and L-asparagine are 4.6 and 4.4 X 10(-6) M, respectively. The enzyme catalyzes the hydrolysis of the D isomers of glutamine and asparagine at 87 and 69% the rate of the respective L isomers. L-Glutamic acid gamma-monohydroxamate is hydrolyzed at approximately the same rate as L-glutamine. The enzyme is not inhibited by ethylenediaminetetraacetate (0.1 mM), L-glutamate (30 mM), or L-aspartate (30 mM). Ammonium sulfate (10 mM) inhibits the enzymatic activity. The plasma half-life of Pseudomonas 7A glutaminase-asparaginase if 13 hours in normal mice and 43 hours in mice infected with the lactate dehydrogenase-elevating virus.

Amino Acids↗
PubMed1976

In vitro processing of E. coli tRNA precursors.

Using E. coli tRNA precursors isolated from an RNAase P mutant strain, we have studied the steps required for the formation of tRNAs having a mature primary sequence in vitro. Our results suggest that at least three different enzymatic activities can participate in the processing of tRNA precursors.

Escherichia coli↗
PubMed1976

Changes in basic cardiovascular activities during the lifetime of the rat.

In an effort to characterize rats as animal models for aging research, literature dealing with cardiovascular physiology and structure has been reviewed, and available data has been summarized in tabular form. The approach has been to present functional parameters on the basis of rat strain, age, sex, and experiemental condition, in the cases where these are known, so as to develop a unified reference source of baseline data. Hemodynamic properties, such as heart rate, cardiac output, blood pressure and related vascular parameters, have been found to change during the lifetime of rats in such a way as to make the cardiovascular system less efficient in meeting organismal requirements with increasing age. At the cellular level, changes in structure, electrophysiology, and contractile properties have been reported which could account, at least in part, for observed deterioration in cardiovascular function during aging.

Aging↗
PubMed1976

Changes in the biochemistry of the rat heart with increasing age.

Effects of increasing age on biochemical parameters of rat hearts have been summarized, as far as possible, in a descriptive, qualitative manner. Where available, the strain, age, and sex of rats have been included. Due to a lack of uniformity in expressing chemical components and enzyme activities found in rat hearts, it is inappropriate in a review of this type to advance hypotheses regarding the nature of biochemical changes that may be contributing to or be the results of aging processes.

Aging↗
PubMed1976

Some aspects of the central nervous system of the rat during aging.

Literature pertaining to structural and functional changes in rat brain taking place with increasing age has been reviewed. For the most part, only young rats have been studied. Brain weight does not appear to change dramatically throughout the life span of rats beyond early development. Neuronal and neuropil elements appear to undergo age-related changes with respect to size, number, and intercellular relationships. Intracellular organelles show evidence of degeneration. Additional studies on central nervous system function in relation to age are required in order to ascertain the meaning of particular structure changes.

Aging↗
PubMed1976

Arginine decarboxylase from a Pseudomonas species.

An arginine decarboxylase has been isolated from a Pseudomonas species. The enzyme is constitutive and did not appear to be repressed by a variety of carbon sources. After an approximately 40-fold purification, the enzyme appeared more similar in its properties to the Escherichia coli biosynthetic arginine decarboxylase than to the E. coli inducible (biodegradative) enzyme. The Pseudomonas arginine decarboxylase exhibited a pH optimum of 8.1 and an absolute requirement of Mg2+ and pyridoxal phosphate, and was inhibited significantly at lower Mg2+ concentrations by the polyamines putrescine, spermidine, and cadaverine. The Km for L-arginine was about 0.25 mM at pH 8.1 AND 7.2. The enzyme was completely inhibited by p-chloromercuribenzoate. The inhibition was prevented by dithiothreitol, a feature that suggests the involvement of an -SH group. Of a variety of labeled amino acids tested, only L-arginine, but not D-arginine was decarboxylated. D-Arginine was a potent inhibitor of arginine decarboxylase with a Ki of 3.2 muM.

Aminooxyacetic Acid↗
PubMed1976

Effect of age on the cardiotoxic action of digitalis.

The cardiotoxic effect of ouabain was explored in rabbits at different ages. The dose of ouabain necessary to produce ventricular tachycardia and death in 1-to 4-week-old rabbits was significantly greater than that required in older animals. In the 1 to 3-week-old animals, ventricular fibrillation occurred only once whereas in animals older than 3 weeks, fibrillation occurred in 23 of 31 animals. A similar pattern of sensitivity to ouabain was observed in bilaterally vagotomized animals. Neither the initial heart rate nor the potassium content of the ventricles in the different age groups appeared to have any influence on the change in the cardiotoxic dose of ouabain. Heart weight increased during the interval when the occurrence of fibrillation increased but it may not fully explain the alteration in the mode of death since fibrillation occurred in some of the younger animals with bilateral vagotomy before the heart weight increased. The catecholamine content of ventricles from 4-to 12-week-old rabbits was significantly greater than that in 1- or 3-week-old rabbits. The age-dependent decrease in the dose of ouabain necessary to produce ventricular tachycardia, ventricular fibrillation and death appeared to be associated with an increase oof ventricular norepinephrine content, although other factors may also play an important part in this response.

Age Factors↗
PubMed1976

A comparative study of the antitumor effectiveness of E. coli and Erwinia asparaginases.

The relative antineoplastic effectiveness of E. coli and Erwinia asparaginases was tested against lymphoid leukemias EARAD-1 and L5178Y/CA55. E. coli and Erwinia asparaginases had similar clearance rates from plasma in mice, and at a dose of 250 IU/kg body weight both enzymes lowered plasma asparagine to undetectable levels. Nevertheless, the dosage of Erwinia asparaginase needed to cause similar prolongation of median survival time in leukemic mice was at least twice that of E. coli asparaginase. The factors which may be responsible for the more potent therapeutic effectiveness of the E. coli asparaginase are discussed.

Animals↗