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Biomedical subjects

R Cooke

Publications and source records attributed to R Cooke.

At least 199 records · Page 11Linked to original sources
PubMed1980

Experimental pigbel: the production and pathology of necrotizing enteritis due to Clostridium welchii type C in the guinea-pig.

An animal model for pigbel in man was developed using guinea-pigs. Intragastric dosing with growing cultures of Clostridium welchii Type C only produced necrotic lesions if protease inhibitors were given as well. beta toxin, which is made by the Type C organism, causes the intestinal damage and is very easily destroyed by proteases. Protease inhibitors in soybean and aprotinin were effectively in inducing disease in animals on a normal diet, while inhibitors in sweet potato, which inhibit only trypsin, were only effective in animals on a low-protein diet. In experiments using intragastric dosing, and in those where cultures and toxic filtrates were injected directly into the jejunum, the animals could be protected with an excess of pancreatic enzymes or by active or passive immunization against beta toxin. The pathology off Type C necrotizing enteritis in guinea-pigs had the macroscopic and microscopic features of pigbel in man. These experiments suggested the basic importance of a low-protein diet and dietary trypsin inhibitors in the pathogenesis of pigbel in man.

Animals↗
PubMed1979

Stability of polyadenylic and polyadenylated ribonucleic acids in radish (Raphanus sativus) seedlings.

The stability of polyadenylic acid and polyadenylated RNA was investigated in young radish (Raphanus sativus) seedlings. We first studied the decay of poly(A) content, using a [3H]poly(U) assay, following a complete block of transcription by cordycepin (200 microgram/ml). Two lifetime classes of polyadenylic acid have been determined in these seedlings: a short-lived component with a half-life of 30 min which represents 60% of poly(A) and a more stable component with varying half-lives of which the majority range from 4-10 h and a few are considerably longer. During this period rRNA was shown to decay linearly, taking about 41 h for half of this RNA to disappear. The life-time of the other moiety of polyadenylated-RNA was analysed by continuous labelling with [3H]uridine. We have been able to demonstrate that a significant part of the mRNA molecules turns over with a half-life similar to that of the more slowly turning-over poly(A). No evidence could be obtained for rapidly turning-over messenger RNA. Thus the rapidly turning over poly(A) could correspond to a poly(A) turn-over independent of the remainder of the sequence. When labelling was very long, an apparent steady-state was reached and we determined the polyadenylated RNA content of seedlings to be 2.2% of whole cell RNA. Finally, these results were compared with those previously obtained in studying early germination of radish embryo axes. In contrast with stored mRNA which is rapidly degraded following imbibition, part of the mRNA present in 22 h old seedlings is stable for several hours.

Deoxyadenosines↗
PubMed1979

Contraction of glycerinated muscle fibers as a function of the ATP concentration.

We have measured the force-velocity curves of glycerinated rabbit psoas fibers over a range of ATP concentration from 2.5 microM to 5 mM. As the ATP concentration is increased, the isometric tension increases to a maximum around 50 microM, then decreases to a plateau at 70% of the maximum by 1 mM ATP. At low ATP concentrations the maximum velocity of contraction is low and increases with increasing ATP, reaching a plateau at approximately 2 lengths per second by 1 mM ATP. Our studies suggest that the binding of ATP dissociates the myosin head from actin in the contracting muscle, a reaction similar to that seen in solution. We have constructed models of the actin-myosin-nucleotide interactions based on a kinetic scheme derived from solution studies. The fit of these models to the data shows that the rates of some reactions in the fiber must be considerably different from the rates of the analogous reactions in solution. The data is best fit by models in which head attachment occurs rapidly at the beginning of a power stroke, head detachment occurs rapidly at the end of the power stroke, and the force produced by a myosin head in a power stroke is independent of velocity.

Adenosine Triphosphate↗
PubMed1979

Phosphorylation of uterine smooth muscle myosin permits actin-activation.

Myosin was purified from ovine uterine smooth muscle. The 20,000 dalton myosin light chain was phosphorylated to varying degrees by an endogenous Ca2+ dependent kinase. The kinase and endogenous phosphatases were then removed via column chromatography. In the absence of actin neither the size of the initial phosphate burst nor the steady state Mg2+-dependent ATPase activity were affected by phosphorylation. However, phosphorylation was required for actin to increase the Mg2+-dependent ATPase activity and for the myosin to superprecipitate with actin. Ca2+ did not affect the Mg2+-dependent ATPase activity in the presence or absence of action or the rate or extent of superprecipitation with actin once phosphorylation was obtained. These data indicate that: 1) phosphorylation of the 20,000 dalton myosin light chain controls the uterine smooth muscle actomyosin interaction, 2) in the absence of actin, phosphorylation does not affect either the ATPase of myosin or the size of the initial burst of phosphate and, 3) Ca2+ is important in controlling the light chain kinase but not the actomyosin interaction.

Actins↗
PubMed1978

Contractile properties of actomyosin from human blood platelets.

Actomyosin was purified from human blood platelets and used to form threads via extrusion. A sensitive tensiometer was employed to measure isometric tension and velocity of isotonic shortening of the threads in the presence of MgATP. Using fully phosphorylated myosin, we obtained values for maximum isometric tension (Po) and maximum velocity of contraction (V max) that were similar to those reported for threads composed of skeletal muscle actomyosin. Po was found to be directly proportional to the level of phosphorylation of the 20,000-dalton myosin light chain. We also studied the effect of phosphorylation on superprecipitation of platelet actomyosin. Fully phosphorylated myosin produced rapid clearing and superprecipitation, while myosin with a low level of bound phosphate underwent rapid clearing but did not superprecipitate. We have concluded from these results that: 1) the interaction between platelet actin and myosin produces tension and motion that is similar to that produced by skeletal muscle actin and myosin and 2) phosphorylation of the 20,000-dalton myosin light chain in important in controlling the production of force by platelet actin and myosin.

Actomyosin↗
PubMed1978

Effect of the protein-synthesis-initiation inhibitor 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide on ribonucleic acid synthesis in radish seedlings.

2-(4-Methyl-2,6-dinitroanilino)-N-methylpropionamide, an inhibitor of initiation of protein synthesis in plants, selectively alters rRNA synthesis. Ribosomal genes are transcribed in the absence of protein synthesis, but processing of the transcripts is impaired. This results in an accumulation of the 2.3 X 10(6)-dalton pre-rRNA. Synthesis of polyadenylated RNA is not affected by the drug.

Aniline Compounds↗
PubMed1977

Tension generation by threads of contractile proteins.

Threads of contractile proteins were formed via extrusion and their isometric tensions and isotonic contraction velocities were measured. We obtained reproducible data by using a new and sensitive tensiometer. The force-velocity curves of actomyosin threads were similar to those of muscle, with isometric tensions of the order of 10g/cm2 and maximum contraction velocites of the order of 10(-2) lengths/s. The data could be fitted by Hill's equation. Addition of tropomyosin and troponin to the threads increased isometric tension and maximum contraction velocity. Threads which contained troponin and tropomyosin required Ca++ for contraction and the dependence of their isometric tension on the level of free Ca++ was like that of muscle. The dependence of tension or of contraction velocity upon temperature or upon ionic strength is similar for actomyosin threads and muscle fibers. In contrast, the dependence of most parameters which are characteristic of the actomyosin interaction in solution (or suspension) upon these variables is not similar to the dependence of the muscle fiber parameters. The conclusion we have drawn from these results is that the mechanism of tension generation in the threads is similar to the mechanism that exists in muscle. Because the protein composition of the thread system can be manipulated readily and because the tensions and velocities of the threads can be related directly to the physiological parameters of muscle fibers, the threads provide a powerful method for studying contractile proteins.

Actins↗
PubMed1975

Supramolecular forms of actin from amoebae of Dictyostelium discoideum.

Actin purified from amoebae of Dictyostelium discoideum polymerizes into filaments at 24 degrees upon addition of KCl, as judged by a change in optical density at 232 nm and by electron microscopy. The rate and extent of formation of this supramolecular assembly and the optimal KCl concentrations (0.1 M) for assembly are similar to those of striated muscle actin. The apparent equilibrium constant for the monomer-polymer transition is 1.3 muM for both Dictyostelium and muscle actin. Although assembly of highly purified Dictyostelium actin monomers into individual actin filaments resembles that of muscle actin, Dictyostelium actin but not muscle actin was observed to assemble into two-dimensional nets in 10 mM CaCl2. The Dictyostelium actin also forms filament bundles which are 0.1 mum in diameter and which assemble in the presence of 5 mM MgCl2. These bundles formed from partially purified Dictyostelium actin preparations but not from highly purified preparations, suggesting that their formation may depend on the presence of another component. These actin bundles reconstituted in vitro resemble the actin-containing bundles found in situ by microscopy in many non-muscle cells.

Actins↗