Correlation between operation of a volume control system (independent of Na+-K+ -ATPase) and membrane vesicle structure was examined in strips of rat myometrium made Na-rich by incubation in Krebs-Ringer solutions at 5 degrees C. Some pieces of tissue were analyzed for Na+, K+, ATP and water contents before and after rewarming to 37 degrees C. Other pieces of tissue were prepared and examined in the electron microscope. The membrane vesicles along the surface of the muscle cells were reduced from the numberin fresh tissues made Na+-rich by overnight incubation in K+-free Ringer solution at 5 degrees C. Rewarming of Na+-rich tissues under conditions thought to inhibit Na+-K+-ATPase caused the loss of Na+ with water and with utake of K+ but the vesicles did not increase in number. Na+-K+ATPase activity was suggested to inhibit vesicle formation by competing for ATP. The loss of water and increase in vesicle number was Ca2+-dependent but did not require Na+. Inhibition of the volume control system by iodoacetamide, Ca2+-free solution and other procedures resulted in swelling of membrane vesicles. The membrane vesicles were suggested to be sites of a mechanochemical system of volume control and the mechanochemical step was suggested to involve discharge of membrane vesicles.
A method was developed for studying the effect of some neurotransmitters and drugs on the rate of movement and the chemotactic value of the plasmodium of Physarum polycephalum. Epinephrine (adrenaline) at a concentration of 1 mg/ml, reduced the rate of movement and shortened the length of the cycles of shuttle streaming, but did not affect the chemotactic response. The drugs DL-amphetamine, cannabinol and heroin diminished the rate of movement, whereas Na-barbitol misled the chemotactic response.
A previously existing model of cross-bridge kinetics is modified to make it applicable to cardiac muscle and incorporated into a macroscopic model of isolated heart muscle. Equations are formulated which describe the responses of this model during simulated isometric and isotonic contractions. These equations allow one to calculate the time variation of the activation parameter in the model when given the contraction time history, i.e. the time course of length and tension changes. The activation parameter is defined as the instantaneous rate constant for cross bridge attachment. We calculate the time course of the activation parameter with the model's responses set equal to the measured responses of isolated cat papillary muscle and the model parameters chosen appropriately for cat papillary muscle. It is found that in order for the model and muscle response to match, the degree of activation of the muscle model must first increase and then decrease with shortening. The behavior of the activation parameter in the muscle model is consistent with physiological investigations which suggest that shortening in cardiac muscle is associated with both activation and deactivation.
A continuum theory is proposed for the chemically controlled cytoplasmic streaming observed in pseudopodium extension in Chaos Carolinensis. Amoeboid cytoplasm is assumed to consist of submicroscopic contractile fibers bathed by viscous fluid. The fiber constituent models the actin-like and myosin-like contractile machinery known to be present in Chaos Carolinensis cytoplasm. A "trigger chemical", produced at the pseudopodium tip, moves by diffusion in, and convection by, the viscous fluid, and causes the contractile fibers to contract in their own length. The contracting fibers, attached at the tip and running continuously back toward the amoeba cell body, pull the fluid constituent of the cytoplasm forward and ultimately crosslink to form the outer gel tube of the advancing pseudopodium. That is, streaming cytoplasm is modeled as a two constituent porous medium, with the fluid constituent free to flow through a porous matrix of oriented (contractile fiber) rods, while the matrix of rods itself moves as the fibers contract, with fiber contraction controlled by a trigger chemical born by the fluid constituent. According to this theory, in the region behind the advancing pseudopodium tip, the contractile fiber rods move forward toward the tip faster than the fluid constituent. The hydrostatic pressure in the fluid therefore increases from the cell body toward the tip (Just the opposite from flow driven by pressure excess generated in the cell body). The excess of hydrostatic pressure above ambient built up at the tip provides the force to roll out the advancing pseudopodium tip. The cell membrane plays no active mechanical role. The mathematical transcription makes a precise theory of R. D. Allen's "frontal (or fountain zone) contraction model". The general system of coupled, non-linear, partial differential equations is solved for its simplest non-trivial special case, that of a steady-state motion, as seen from a coordinate system attached to the advancing tip. Solutions exist, and, for each distinct forward speed (which is left to the discretion of the amoeba) the solution is unique. The theory predicts both upper and lower bounds for possible pseudopodium lengths.
The technique for mechanical dissection of microscopic myofibrilar bundles containing few myofibrils is described. A sensitive electrooptical tension transducer capable of resolving the tension generated by such myofibrilar bundles to within a fraction of a percent is used to study the response of the preparations to low ATP concentrations. The rate of tension development decreased with a decrease in ATP concentration. Below 10(-6) M ATP the myofibrils did not demonstrate any mechanical activity at all. These findings are discussed in terms of the kinetics of the cross-bridge cycle.
The general problem of transconformation of one helical form of protein to another is considered from a topological point of view. A notation is presented which reflects the topology of the bonding. Any helix belongs to one of two geometrical classes, the positive and negative classes. The fundamental mechanism of transconformation between helices of the same class is the edge dislocation. It has two limiting modes of propagation: glide and climb. The first appears as a caterpillar-like wave of slip that travels along the peptide chain. If the second occurs then it would be the vehicle of change in number of peptide chains. The fundamental mechanism of transconformation between molecules of opposite classes is a process we call flipping, which also probably travels as a wave. Examples of transconformation including alpha DL leads to pi 4 DL in poly-gamma-benzyl-glutamate and alpha leads to beta in keratin, are discussed.
A stochastic computational method developed for analysis of two-state cross-bridge models was extended and used to compute the oscillatory movement generated by three-state cross-bridge models containing a rate function proportional to ATP concentration. Only one of the possible three-state models appears satisfactory; with this model, the frequency of oscillation, at constant amplitude, responds to changes in both ATP concentration and viscosity in the same way as real flagella. In this model, ATP binding causes cross-bridge detachment, which is rate limiting at low ATP concentrations; while at high ATP concentrations a transition between two attached states limits the rate of cross-bridge detachment. Since this model agrees with observations on actomyosin ATPase kinetics, the data on flagellar oscillation frequency support the idea that the movement-generating mechanisms of flagella and muscle are similar.
A circlet of 9 interacting microtubular doublets generates less bending moment at low bending rates, but allows bending moment to be generated at higher bending rates, and has an energy efficiency at least 92% as great as an arrangement with all the interactions between microtubular doublets in a plane parallel to the bending plane. The axonemal arrangement has no significant effect on the shape of the normalized relationship between active shear moment and shear rate.
This paper deals with elementary thermodynamic considerations applicable to mechano-chemical cycles. It shall review concepts about the efficiency of these cycles and then suggest an extension of the concept of the Availability Function to be called the Mechano-Chemical Availability Function.
The dielectric dispersion of G-actin was 7 X 10(6) Hz, and the low frequency reduced dielectric increment 0.99 +/- 0.15 ml/mg. The dielectric increment of F-actin in the range 10(5) to 10(8) Hz was very low, about 0.3.
Measurements of birefringence, ultraviolet dichorism and quasielastic light scattering were carried out on F-actin in solution and on the thin filaments of glycerinated myofibrils. The birefringence of the I-bands of myofibrils was of the same order of magnitude as that of F-actin or the F-actin-tropomyosin-troponin complex oriented in vitro at the same concentration. The ultraviolet dichroism spectrum of the I-bands was very similar to that of F-actin or the F-actin complex in vitro, which is due to orientation of bound ADP and tryptophan residues in F-actin. Quasielastic light scattering measurements, electronmicroscopic observations and the analyses of the electro-optic effect of the I-bands suggested approximately the same flexibility for F-actin in vitro and for the thin filaments in vivo. These optical measurements which were made under various conditions provide evidence for a conformational change induced by calcium ions in F-actin both in vivo and in vitro. This conformational change was found to be amplified by the interaction of F-actin with myosin. This is a brief review of our investigation on the dynamics of F-actin and the thin filament in vivo and in vitro by optical methods.
The present paper is an analytical review of the information available on amoeboid movement in human leucocytes. The reported evidence suggests that leucocyte locomotion is due to pressure developed in the cell cortex in the middle and posterior parts of the moving cell, that 4 nm fibrils may provide at least part of the ultrastructural basis of locomotion, that actin-like and myosin-like proteins may be involved in the mechanism of movement and that ATP may serve as an energy source. Leucocyte motility appears to be governed mainly by factors produced in the external medium. Neutrophil chemotaxis is the most antitubulin-susceptible cell mechanism known; from this observation an essential role of microtubule redistribution in chemotaxis is inferred. In contrast, the random movement of neutrophils is not appreciably affected by antimitotic concentrations of antitubulins. Amoeboid movement seems to be an important mechanism in the short-distance locomotion and immunological functions of leucocytes.
A new protein component was found in heavy meromyosin and in subfragment-1 (S-1) prepared by chymotrypsin digestion of pig cardiac myosin in the presence of Ca2+. The molecular weight of this protein was estimated as 15,000 dalton. It was able to bind Ca2+ and showed a similar UV absorption spectrum to that of the g2 light chain. Heavy meromyosin and subfragment-1 which contained the 15,000 dalton component incorporated exogenous g2 and the 15,000 dalton component disappeared after such treatment. We concluded that the 15,000 dalton component was produced from g2 by limitted proteolysis. The subfragment-1 was separated into two protein fractions in equal yield by recycling the gel filtration. One contained the 15,000 dalton component and was able to bind Ca2+ while the other did not contain the component and was unable to bind Ca2+. According to analysis by SDS gel electrophoresis, the large polypeptide chain (the f component) of the first S-1 was approximately 5,000 dalton larger than the f component of the second S-1. The polypeptide corresponding to 5,000 dalton was designated polypeptide-C, because it was released from the C terminal of the f component. It seems to be essential for the attachment of the Ca2+-binding light chain g2. The location of g2 in myosin may thus be at the polypeptide-C which links the head to the tail of myosin.
Correlation between operation of a volume control system (independent of Na+-K+ -ATPase) and membrane vesicle structure was examined in strips of rat myometrium made Na-rich by incubation in Krebs-Ringer solutions at 5 degrees C. Some pieces of tissue were analyzed for Na+, K+, ATP and water contents before and after rewarming to 37 degrees C. Other pieces of tissue were prepared and examined in the electron microscope. The membrane vesicles along the surface of the muscle cells were reduced from the numberin fresh tissues made Na+-rich by overnight incubation in K+-free Ringer solution at 5 degrees C. Rewarming of Na+-rich tissues under conditions thought to inhibit Na+-K+-ATPase caused the loss of Na+ with water and with utake of K+ but the vesicles did not increase in number. Na+-K+ATPase activity was suggested to inhibit vesicle formation by competing for ATP. The loss of water and increase in vesicle number was Ca2+-dependent but did not require Na+. Inhibition of the volume control system by iodoacetamide, Ca2+-free solution and other procedures resulted in swelling of membrane vesicles. The membrane vesicles were suggested to be sites of a mechanochemical system of volume control and the mechanochemical step was suggested to involve discharge of membrane vesicles.
We tested the hypothesis that membrane vesicles of smooth muscle function as organelles controlling cell volume through a mechanochemical mechanism not involving Na+-K+ dependent membrane ATPase. Pieces of rat myometrium were incubated under various conditions at 25 degrees C, and then were analyzed after various times for Na+, K+, ATP and water contents or were prepared and examined in the electron microscope. Metabolic inhibition with iodoacetate (IAA) + dinitrophenol (DNP) rapidly depleted ATP, then decreased membrane vesicle number and increased vesicle size. Thereafter K+ loss, Na+ gain and water gain occurred. Slower depletion of ATP by treatment of tissues with IAA or ethacrynic acid produced similar, but delayed effects. Treatment with DNP alone, DNP in glucose-free Krebs-Ringer or glucose-free solution bubbled with N2 partly depleted the tissues of ATP but did not markedly affect the membrane vesicles or tissue water content. Ouabain affected neither ATP contents of tissues nor the numberof membrane vesicles, but produced large intracellular vesicles. The membrane vesicles were suggested to be sites of a mechanochemical volume control system.
A model of bacterial flagellar drive by cytomembrane streaming is described and applied to experiments of bacterial propulsion under varying viscous load. The theory predicts a linear dependence of the reciprocal propulsion velocity on the viscosity of the suspension medium, if the velocity of cytomembrane streaming far from the basal body of the flagella is assumed independent of the external viscosity. The theoretical predictions are in good agreement with experiments on free-swimming and on tethered bacteria. From comparison of the theory with experiments, the surface viscosity of the bacterial cytomembrane is evaluated for different bacterial species and turns out to be in the range observed experimentally on lipid monolayers.
Using glutaric dialdehyde, the muscle proteins myosin, actin, actomyosin and heavy meromyosin subfragment-1 (S-1) have been immobilized on capron fibers. The ATPase activity of myosin and its capability to interact with actin have been preserved whereas the ATPase activity of its subfragment decreased significnatly. Immobilization on capron fibers changes the pH dependence of the ATPase activity of myosin and of S-1 shifting the maximum towards the acid zone (pH 5.5) and increases the thermal stability of the enzyme. Calcium ions produce a stimulatory effect on ATPase; Mg2+ions yield no effect on myosin and S-1 but enhance the activity in the case of immobilized actomyosin though to a lesser degree than the ions of Ca2+. Immobilized actin retains its ability to form actomyosin complex.
Wolbachia is the most abundant intracellular symbiont among terrestrial Arthropoda. This bacterium together with other microorganisms, i.e., Cardinium, gained fame mainly as the causative agent of host sex-ratio distortion. Across the impressive diversity of oribatid mites (Acari: Oribatida), the microbes have been found in both parthenogenetic (Oppiella nova, Ceratozetes thienemanni, Hypochthonius rufulus) as well as sexually-reproducing (Gustavia microcephala, Achipteria coleoptrata, Microzetorchestes emeryi, Damaeus onustus) species. Wolbachia found in Oribatida represents supergroup E and is related to bacterial endosymbionts of springtails (Hexapoda: Collembola). Cardinium identified in O. nova and M. emeryi belongs to phylogenetic group A. In turn, Cardinium from A. coleoptrata constitutes a new separate group E. The occurrence of these bacterial endosymbionts in parthenogenetic and sexual oribatid mites species may suggests a different function other than manipulating host reproduction. Indeed, endosymbionts may have various "shades" of functions in invertebrate hosts, some of which cannot be excluded in the oribatid mites, e.g., enriching a nutrient-limited diet with B vitamins or contributing to host adaptation to colder and harsher climates. Nevertheless, the mystery behind the roles of bacteria in Oribatida still needs required to be unraveled.
