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Biomedical subjects

M M Jones

Publications and source records attributed to M M Jones.

At least 235 records · Page 13Linked to original sources
PubMed1978

How patients use domiciliary oxygen.

Forty-five patients in Southampton who received domiciliary oxygen were visited at home to find out how they used and coped with their oxygen. Generally, the organisation and administration of supplies presented no problems, nearly all the apparatus complied with the drug tariff, and most patients coped well with the equipment. Only two patients were taking oxygen for prescribed periods; the others were taking it when necessary for symptomatic relief. No patient received oxygen for over five hours daily. Most patients thought that they were helped by oxygen, but only four said that it allowed them to increase their level of activity, and the overall benefit seemed slight. This was partly because oxygen was usually limited to one room, so patients used oxygen after rather than during exercise. The amount of oxygen consumed differed widely, ranging from three and a half cylinders a week in three patients to less than one cylinder in six months in 17 patients. The average yearly cost of oxygen per patient ranged from 500 pounds in patients consuming one cylinder or more per week, to 15 pounds in those consuming less than one cylinder in six months. The main cost of domiciliary oxygen is determined by the number of cylinder refills, so patients who use it infrequently are a relatively small drain on resources.

Aged↗
PubMed1978

Osmotic adjustment in leaves of sorghum in response to water deficits.

The relationships among the total water potential, osmotic potential, turgor potential, and relative water content were determined for leaves of sorghum (Sorghum bicolor [L.] Moench cvs. ;RS 610' and ;Shallu') with three different histories of water stress. Plants were adequately watered (control), or the soil was allowed to dry slowly until the predawn leaf water potential reached either -0.4 megapascal (MPa) (treatment A) or -1.6 MPa (treatment B). Severe soil and plant water deficits developed sooner after cessation of watering in ;Shallu' than in ;RS 610', but no significant differences in osmotic adjustment or tissue water relations were observed between the two cultivars. In both cultivars, the stress treatments altered the relationship between leaf water potential and relative water content, resulting in the previously stressed plants maintaining higher tissue water contents than control plants at the same leaf water potential. The osmotic potential at full turgor in the control sorghum was -0.7 MPa: stress pretreatment significantly lowered the osmotic potential to -1.1 and -1.6 MPa in stress treatments A and B, respectively. As a result of this osmotic adjustment, leaf turgor potentials at a given value of leaf water potential exceeded those of the control plants by 0.15 to 0.30 MPa in treatment A and by 0.5 to 0.65 MPa in treatment B. However, zero turgor potential occurred at approximately the same value of relative water content (94%) irrespective of previous stress history. From the relationship between turgor potential and relative water content there was an approximate doubling of the volumetric elastic modulus, i.e. a halving of tissue elasticity, as a result of stress preconditioning. The influence of stress preconditioning on the moisture release curve is discussed.

Journal Article↗
PubMed1978

The relative effectiveness of some chelating agents as antidotes in acute cadmium poisoning.

An examination has been made of the relative effectiveness of three chelating agents in reducing lethality in acute cadmium poisoning. The chelating agents used were sodium 2,3 dimercaptosulfonate (DMPS), N-Acetyl d,1 penicillamine (NAPA), and 2,3 dimercaptosuccinic acid (DMSA). For cadmium acetate administered ip at a level of 16.9 mg/kg, the oral administration of the chelating agents at a 20:1 mole ratio in three doses subsequent to the cadmium acetate at 20 minutes, 90 minutes, and 210 minutes resulted in a significant enhancement of the survival rate for all three compounds. At this level none of the control animals survived beyond 2 days. On the basis of the experiments carried out here the survival rates decreased in the order sodium 2,3 dimercaptopropane-sulfonate greater than 2,3 dimercaptosuccinic acid greater than N-Acetyl d,l penicillamine. In a study of the effect of the mole ratio of the chelating agent sodium 2,3 dimercaptopropanesulfonate to cadmium acetate on the survival rate, it was found that the survival rate attained a maximum for values between 20 and 60 and dropped off at both higher and lower values. It was also found that for at least one set of conditions, younger animals were better able to survive the administration of cadmium acetate and the antidote than older animals.

Animals↗
PubMed1976

Scanning gel chromatography: determination of transport parameters from dynamic profiles measured at low solute concentration.

Direct optical scanning of solute boundaries in large zone gel chromatography experiments provides an accurate means of determining boundary profile shapes and rates of motion. A method has been developed for correcting such boundaries to a constant time frame, eliminating the distortion which arises from finite column scanning rate. Centroids of the corrected profiles can be used to determine the partition cross section for the solute of interest. The partition cross section and flow rate determine translational motion within the column. The axial dispersion coefficient, L, which characterizes rate of boundary spreading may also be calculated from the profiles. In order to explore these procedures a study of four noninteracting solutes was conducted. Partition cross sections determined from rates of motion of boundary centroids were found to be in good agreement with those determined by the equilibrium saturation method on the same column. In order to explore the lowest concentration limits of the technique and to illustrate the boundary characteristics for a self-associating solute, a study of carboxyhemoglobin was conducted over a wide concentration range. From measurements at 220 nm the lowest concentration where useful data could be obtained was 2 micrograms per ml (0.12muM heme). These results establish validity of the procedures used in analyzing the rates of boundary transport and in studying solute transport over a wide range of conditions.

Animals↗
PubMed1976

Active enzyme gel chromatography. I. Experimental aspects.

Transport properties of active enzyme species can be studied effectively by layering a small band of enzyme-containing sample on a gel chromatographic column previously saturated with substrate. The column is optically scanned at successive time intervals to yield profiles representing the appearance of chromophoric product or disappearnce of chromophoric substrate. These profiles permit determination of the specific activity and rate of transport of the active species. Initial studies on mechanic of the technique establish the feasibility of accurately determining transport properties of active enzyme species chromatographed on gel columns. Illustrative results are presented for L-glutamate dehydrogenase and for homoserine dehydrogenase studied in both forward and reverse reactions. It is shown that the partititon cross sections derived from the rates of motion of catalytic activity are the same as those determined by equilibrium saturation experiments which directly measure the degree of partitioning by the protein. These results establish the validity of the technique for a variety of future studies. Active enzyme gel chromatography appears comparable in precision to the active enzyme sedimentation technique at current stages of development.

Alcohol Oxidoreductases↗
PubMed1975

Aspartokinase I-homoserine dehydrogenase I of Escherichia coli K12 (lambda). Activation by monovalent cations and an analysis of the effect of the adenosine triphosphate-magnesium ion complex on this activation process.

The dehydrogenase activity of the aspartokinase I-homoserine dehydrogenase I complex isolated from Escherichia coli K12 is subject to a cooperative activation by K+ or Rb+, which is characterized by a Hill coefficient of approximately 2. Ionic strength has little effect on the Hill coefficient for this activation process; however, high ionic strength appears to increase the enzyme's affinity for K+ and decrease its affinity for Rb+. The Vmax of the K+-activated dehydrogenase is greater than that of the Rb+-activated dehydrogenase. The results of a study of the competition between K+ and Rb+ in the activation process suggest the presence of an activated species containing both K+ and Rb+. The cooperative activation by K+ is antagonized by Na+ via a process that is noncooperative with respect to Na+. The MgATP-2- complex, a substrate for the kinase activity of aspartokinase I-homoserine dehydrogenase I, has a marked effect on the K+ activation of the dehydrogenase activity. Kinetic studies of this effect of MgATP-2- on the K+ requirement of the dehydrogenase at pH 8.9 indicate that: (a) activation by a monovalent cation is essential in the presence as well as in the absence of MgATP-2-; (b) the concentration of K+ required to activate fully the dehydrogenase is reduced in the presence of MgATP-2-; (c) activation of the dehydrogenase by K+ is noncooperative in the presence of MgATP-2-; and (d) the maximum velocity for the dehydrogenase catalyzed oxidation of homoserine is greater in the presence of MgATP-2- than in its absence. Based on these results, a simple model consistent with these data is proposed. Destruction of the kinase activity and the threonine sensitivity of the aspartokinase-homoserine dehydrogenase complex by treatment with 5,5'-dithiobis(2-nitrobenzoic acid) or by incubation at pH 9 also converts the K+ activation of the dehydrogenase from a cooperative to a noncooperative process. Marked protection of the enzyme against loss of threonine sensitivity at pH 9 is afforded by MgATP-2- plus K+ and homoserine. The apparent molecular radius of the enzyme complex as determined by gel filtration at pH 8.85 in the presence of threonine or MgATP-2- plus K+ and homoserine is dependent on the enzyme concentration. The observed apparent molecular radii of 70 A at high enzyme concentrations and 61 A at low enzyme concentrations are consistent with the enzyme's undergoing a concentration-dependent dissociation from a tetrameric to a dimeri

Adenosine Triphosphate↗