Parallel response of myofibrillar contraction and relaxation to four different nucleoside triphophates

The Mg chelates of ITP, GTP, and UTP in addition to that of ATP were shown to be capable of causing complete relaxation of myofibrils as indicated by the complete inhibition of syneresis and the reduction of the NTPase activity to that of isolated myosin. For ITP and GTP the required concentrations were about 100 times higher than those for ATP, whereas UTP was maximally effective also in low concentrations (0.2 mM). For all NTP's the concentrations for relaxation were related to those necessary for contraction so that NTP concentrations which gave 80-90% maximal NTPase activity in the presence of Ca caused complete relaxation in the absence of Ca. Thus, these experiments do not support the view that relaxation is caused by the binding of NTP to a special inhibitory site but are quite compatible with the idea that relaxation depends on the extent to which the hydrolytic site is saturated with NTP. The Ca concentration required for contraction depends on the nature of the NTP base and its concentration; it is lower for ITP than for ATP and decreases with decreasing concentrations of ITP.

The mechanism of the action of caffeine on sarcoplasmic reticulum

Evidence is presented that caffeine does not act on the mitochondrial Ca uptake system and that its effect cannot be attributed to the accumulation of adenosine 3',5'-phosphate. Two distinct caffeine effects are described. At high ATP concentrations caffeine decreases the coupling between ATP hydrolysis and Ca inflow. It either inhibits inflow without any inhibition of the rate of ATP hydrolysis, or it stimulates the ATPase activity without stimulating Ca inflow. These high ATP concentrations (much higher than needed for the saturation of the transport ATPase) greatly reduce the control of the turnover rate of the transport system, by accumulated Ca. At low ATP concentrations when the transport system is under maximal control by accumulated Ca, caffeine inhibits the ATPase activity without affecting the rate of Ca inflow.

The relationship between caffeine contracture of intact muscle and the effect of caffeine on reticulum

At concentrations between 1 to 10 mM, caffeine reduced the Ca-accumulating capacity of fragmented reticulum obtained from frog and rabbit muscle. With 8 mM caffeine enough Ca was released from frog reticulum to account for the force of the contracture. Caffeine did not affect all reticulum membranes equally. The fraction which was spun down at 2000 g was more sensitive than the lighter fractions. The percentage of the total accumulated Ca released by caffeine decreased with decreasing Ca content of the reticulum. In parallel with their known effects on the caffeine contracture, a drop in temperature increased the caffeine-induced Ca release while procaine inhibited it. Caffeine also inhibited the rate of Ca uptake, which may in part account for the prolongation of the active state caused by caffeine.

Analysis of polar and nonpolar tryptophan mutants by derepression kinetics

A comparison of the rates of synthesis of the tryptophan biosynthetic enzymes of Salmonella typhimurium under derepression showed that the genes of the trp operon can be expressed in a coordinate fashion in auxotrophs carrying nonpolar mutations. This coordination disappeared in trpA polar mutants. The loss of coordination affected only trpB, the second gene in the operon, which was always more drastically affected than the three distal genes. Polar mutations in trpA, the first gene of the trp operon, reduced the rates of synthesis of the tryptophan biosynthetic enzymes under conditions of derepression. When these rates were measured and correlated with the map position of each polar mutation, a polarity gradient of decreasing intensity (moving distally from the operator end of the gene) was obtained. Certain mutations ("unusual mutations") mapping at the operator distal end of trpA, and considered by other workers to correspond to the operator proximal end of trpB, were found to be polar. The bearing of our observations on the question of coordinate versus semicoordinate expression of the trp genes and the status of the "unusual mutations" is discussed.

Polar and antipolar mutants in the tryptophan operon of Salmonella typhimurium

Polar mutations in trpA, the first structural gene of the tryptophan operon of Salmonella typhimurium, have an uncoordinate effect on the expression of the distal genes, with trpB, the second gene, being more drastically affected than the last three. A number of these polar mutant strains grow very poorly on anthranilic acid-supplemented minimal medium. By selecting for more rapid growth in the presence of anthranilic acid, secondary mutant clones showing a correction of the polar effect were isolated. A few of these were analyzed and shown to contain deletions of various segments of the trpA gene. Ten randomly isolated deletion mutants missing various segments of the trp operon were analyzed for possible pleiotropic effects. Five of them showed a pleiotropic effect of some sort and five did not. Of those showing pleiotropic effects, one had lost the promotor-like elements necessary to initiate expression of the operon, three showed possible antipolar effects, and one showed both polar and antipolar effects simultaneously.

Studies in the epidemiology and control of seasonal conjunctivitis and trachoma in southern Morocco

It has been noted in many parts of the world that bacterial conjunctivitis is a major cause of total or partial loss of vision. In addition, trachoma is aggravated if there are associated bacterial infections and these lead to more frequent corneal complications.In the trials described the seasonal variation of bacterial infections was studied in addition to trachoma in 3 pilot sectors in southern Morocco. The frequency of complications and late sequelae from these infections in the whole population of these sectors was also studied.In one of the sectors 3 different methods of limiting the regular seasonal increase in bacterial infections and of curing trachoma were evaluated separately or in combination. These included the effect of fly-suppression on the transmission of infection, a possible method of chemoprophylaxis, and intermittent treatment with chlortetracycline ointment.The effect of the latter, when applied to a whole population group by auxiliary personnel, was compared with the long-term effect of self-treatment, in this and the two other sectors.The total observation period covered 12 years.

The effect of the replacement of calcium by strontium on excitation-contraction coupling in frog skeletal muscle

1. In frog skeletal muscle strontium can replace calcium in potassium contractures for 5 hr, though it is less effective than Ca. Sr can restore the responsiveness to K after it had been lost in the presence of Mn.2. Muscles refractory to caffeine following repeated exposure to it in the absence of Ca, recover in part following addition of Sr.3. The uptake of (85)Sr was increased during mechanical activity, whereas the uptake of (58)Co was not changed. Resting uptake of (58)Co was 3-4 times greater than that of (85)Sr.4. Sr fully activated the myofibrillar adenosine triphosphatase (ATP-ase), though its affinity was about 30 times less than Ca.5. The sarcoplasmic reticulum took up Sr, though less effectively than Ca.