Respiration-associated components of Mollicutes.

No cytochrome pigments were detected by difference (reduced minus oxidized) spectroscopy at liquid nitrogen temperature in whole-cell preparations or membrane fractions of Acholeplasma axanthum S273, Acholeplasma equifetale N93, Acholeplasma granularum BTS39, Acholeplasma laidlawii B-PG9, Acholeplasma modicum PG-49, Acholeplasma oculi 19L, Mycoplasma arginini G230, Mycoplasma arthritidis 07, Mycoplasma pneumoniae FH, and Mycoplasma pulmonis JB. All ten Mollicutes species examined contained iron of unknown function (3.0 to 15.3 nmol of iron per mg of protein). Relatively small amounts of acid-labile sulfide were found in all fractions (0.10 to 1.07 nmol of acid-labile sulfide per mg of protein). The data suggest that, as Mollicutes lack cytochrome pigments, they would synthesize most if not all adenosine triphosphate at the substrate level.     

Cytochrome components of plant microsomes.

The electron transport components of the microsomal fraction of cauliflower buds and mung bean hypocotyls were investigated using split-beam and dual wavelength spectrophotometry under a variety of reducing conditions. Cauliflower microsomes were found to contain an ascorbate-reducible component, termed cytochrome b-559.5 [E'0 = +135 +/- 20 mV; lambdamax (reduced minus oxidised) = 559.5, 527 and 429 nm at 23 degrees C], cytochrome b5 [E'0 = -20 +/- 20 mV; lambdamax (reduced minus oxidised) = 556, 526 and 425 nm at 23 degrees C], cytochromes P-450 and P-420. On the basis of binding studies with ethyl isocyanide, degradation of cytochrome P-450 to P-420, redox potential, aniline binding, and relative rates of reduction by NADPH and NADH, it is suggested that the cytochrome P-450 system is analogous to that mammalian microsomes. Other components, reducible only by dithionite, may also be present. Mung bean microsomes were found to contain an ascorbate-reducible component, termed cytochrome b-562 [E'0 = +120 +/- 20 mV; lambdamax (reduced minus oxidised) = 562, 528 and 430 nm at 23 degrees C], cytochrome b5, and a low potential component which was reducible only by sodium dithionite. No cytochrome P-450 or P-420 could be detected. A general method of analysis of the cytochromes was developed and applied to the microsomes from a variety of plant sources. The results indicate that large variations, both in type and amount of components, occur between the microsomes from different plant materials.     

Sulfated components of enveloped viruses.

The glycoproteins of several enveloped viruses, grown in a variety of cell types, are labeled with 35SO4(-2), whereas the nonglycosylated proteins are not. This was shown for the HN and F glycoproteins of SV5 and Sendai virus, the E1 and E2 glycoproteins of Sindbis virus, and for the major glycoprotein, gp69, as well as for a minor glycoprotein, gp52, of Rauscher leukemia virus. The minor glycoprotein of Rauscher leukemia virus is more highly sulfated, with a ratio of 35SO4- [3H]glucosamine about threefold greater than that of gp69. The G protein of vesicular stomatitis virus was labeled when virions were grown in the MDBK line of bovine kidney cells, although no significant incorporation of 35SO4(-2) into this protein was observed in virions grown in BHK21-F line of baby hamster kidney cells. In addition to the viral glycoproteins, sulfate was also incorporated into a heterogenous component with an electrophoretic mobility lower than that of any labeled with 35SO4(-2) and [3H]leucine, this component had a much greater 35S-3H ratio than any of the viral polypeptides and thus could not represent aggregated viral proteins. This material is believed to be a cell-derived mucopolysaccharide and can be removed from virions by treatment with hyaluronidase without affecting the amount of sulfate present on the glycoproteins.     

RS virus components. II. Antigenicity.

Rabbits were immunized with RS virus components, isolated as described previously. The sera were tested by neutralization, double diffusion and complement-fixation. RS virus components induced low titers of precipitating and complement-fixing antibodies, and failed to stimulate the neutralizing antibodies.     

Variance components for discordances.

Tests for biotyping isolates give a result that is classified as either positive or negative, indicative of growth or nongrowth of bacteria. The reproducibility of such tests is measured by the number of discordances in replicates of the same measurement. In this analysis the probability distribution of the number of discordances is estimated for each of several tests in the presence of possible random between-laboratory effects as well as random laboratory-test interactions, which are also estimated.     

The membrane components of crustacean neuromuscular systems. II. Analysis of interactions among the electrogenic components

The present work provides additional evidence for the occurrence of a number of electrogenic components in crustacean and particularly crayfish muscle fibers. It demonstrates that these different components are independent. One or another can be eliminated or modified by various procedures without affecting the rest. However, interactions can occur between the different components. The coupling may be effected by the changes in membrane potential which result from changes in ionic permeabilities or by changes in the membrane conductance. Some interactions of such couplings which can perturb electrophysiological measurements are described and analyzed.     

Replacement of troponin components in myofibrils.

The Ca(2+)-sensitive ATPase activity of rabbit skeletal myofibrils was desensitized by treatment with excess troponin T and was found to be activated irrespective of the Ca2+ concentrations. A SDS-gel electrophoretic study showed that both troponin C and troponin I were removed from the myofibrils on treatment with troponin T. The Ca(2+)- and Sr(2+)- sensitivities of the ATPase of troponin T-treated myofibrils reconstituted with troponin C. I were the same as in the intact myofibrils. The Ca(2+)-activated ATPase of rabbit skeletal myofibrils was also desensitized on treatment with chicken breast troponin T or its 26K fragment. The SDS-gel electrophoretic study revealed that troponin T, in addition to troponin C and troponin I, was also removed from the myofibrils and, instead, chicken breast troponin T or its 26K fragment was incorporated into the myofibrils. The Ca(2+)- sensitivity of myofibrils treated with chicken breast troponin T or its 26K fragment was then regained on reconstitution with troponin C.I. These findings indicate that the change in composition of myofibrils on treatment with troponin T or its 26K fragment is due to the selective replacement of the troponin C.I.T complex in the myofibrils as a whole with troponin T or its 26K fragment.     

Computer simulations of ABC transporter components.

Current computer simulation techniques provide robust tools for studying the detailed structure and functional dynamics of proteins, as well as their interaction with each other and with other biomolecules. In this minireview, we provide an illustration of recent progress and future challenges in computer modeling by discussing computational studies of ATP-binding cassette (ABC) transporters. ABC transporters have multiple components that work in a well coordinated fashion to enable active transport across membranes. The mechanism by which members of this superfamily execute transport remains largely unknown. Molecular dynamics simulations initiated from high-resolution crystal structures of several ABC transporters have proven to be useful in the investigation of the nature of conformational coupling events that may drive transport. In addition, fruitful efforts have been made to predict unknown structures of medically relevant ABC transporters, such as P-glycoprotein, using homology-based computational methods. The various techniques described here are also applicable to gaining an atomically detailed understanding of the functional mechanisms of proteins in general.     

Phosphoproteins: structural components of oncornaviruses.

Oncornaviruses, which contain a virion-associated protein kinase, were found to possess phosphoproteins as virion structural components. One major phosphoprotein common to strains of laboratory and wild mouse oncornaviruses and a strain of feline leukemia virus was shown to be a polypeptide of about 12, 000 mol wt. In addition to this, the Kirsten strain of murine sarcoma virus contained a second major phosphoprotein of about 10, 000 mol wt, and mouse erythroblastosis virus contained a second major phosphoprotein that was either identical to or comigrated with the virion glycoprotein of about 74, 000 mol wt. The major phosphoprotein of RD-114 virus was found to be of about 16, 000 mol wt. The major phosphoamino acid of the 12, 000-mol wt polypeptide of the mouse erythroblastosis virus was identified as phosphoserine, and that of the 16, 000-mol wt polypeptide of the RD-114 virus was identified as phosphothreonine.     

Molecular components of the mitotic spindle.

Mitotic spindles constitute the machinery responsible for equidistribution of the genetic material into each daughter cell during cell division. They are transient and hence quite labile structures, changing their morphology even while performing their function. Biochemical, immunological and genetic analyses of mitotic cells have allowed us to identify a variety of molecules that are recruited to form the spindle at the onset of mitosis. Evaluation of the roles of these molecules in both the formation and in the dynamics of spindle microtubules should be important for understanding the molecular basis of mitosis and its regulation. We have recently identified a novel mitosis-specific microtubule-associated protein (MAP) using a monoclonal antibody probe raised against the mitotic spindles isolated from cultured mammalian cells. This 95/105 kDa antigen represents a unique component of the spindle distinct from any of the other MAPs reported so far. Antibody microinjection resulted in mitotic inhibition in a stage-specific and dose-dependent manner, indicating that the protein is an essential spindle component.     

Interaction of tropomyosin with troponin components.

1. The TN-T and TN-I components of troponin both interact with tropomyosin and cause its precipitation in 0.1 M KC1 at neutral pH. The precipitate contains both end-to-end and side-by-side aggregates of tropomyosin molecules. 2. The TN-T and TN-I components change the band pattern of tropomyosin paracrystals formed in MgC1(2) solutions, although in different ways. TN-T causes the formation of hexagonal net structures, double-stranded net or paracrystals which result from the collapse of the double-stranded net. TN-I at pH 7.9 causes the formation of paracrystals with a 400 A periodic band pattern and a 200 A repeat. The same band pattern can also be seen in tropomyosin paracrystals formed at pH values below 6.0. 3. The TN-C component does not precipitate tropomyosin in 0.1 M KC1. The aggregates of tropomyosin obtained with either TN-T or TN-I can be solubilized by the addition of TN-C. No interaction of TN-C was observed with tropomyosin paracrystals formed in the presence of MgC12.     

Structural components of influenza C virions.

The genome RNA species of influenza type C virions were analyzed by polyacrylamide gel electrophoresis. The pattern obtained was found to resemble those of other influenza viruses. Six RNA species were resolved, with estimated sizes ranging from 0.37 X 10(6) to 1.25 X 10(6) daltons. The internal ribonucleoproteins of influenza C virions were found to sediment heterogeneously in glycerol velocity gradients as demonstrated previously with influenza A/WSN virus. The ribonucleoproteins possessed diameters of 12 to 15 nm, with lengths ranging from 30 to 100 nm. Of the three major virion polypeptides (molecular weights, 88,000, 66,000, and 26,000), only the largest is glycosylated. Similar polypeptide species were present in influenza C virions of five different strains. All three major proteins of influenza C virions possess electrophoretic mobilities distinguishable from those of the major polypeptides of influenza A/WSN. The 66,000-dalton protein is associated with the ribonucleoprotein components. Two additional glycosylated polypeptides, with estimated molecular weights of 65,000 and 30,000, were detected in virions grown in embryonated eggs, but not in virus particles obtained from chicken embryo fibroblasts.     

Mechanical components of motor enzyme function.

Motor enzymes use energy from ATP dephosphorylation to generate movement by a mechanical cycle, moving and pushing in one direction while attached to their cytoskeletal substrate, and recovering by moving relative to their substrate to a new attachment site. Mainstream models assert that movement while attached to the substrate results from preexisting strain in the attached motor. The additional underlying ideas can be described in terms of three components for strain amplification: a rotating lever arm, multiple attached states, and elastic compliance. These components determine how energy is recovered during the mechanical cycle and stored in a strained motor. They may coexist in a real motor; the challenge is to determine the contributions of each component. Because these components can generate similar relationships between strain energy and strain, standard measurements of motor function do not discriminate easily between these components. However, important information could be is provided by observations that suggest weak coupling between chemical and mechanical cycles, observations of negative force and movement events in single motor experiments, and the discovery that two motors that move in opposite directions have very similar structures. In models incorporating changes in conformation between attached states, these observations are only explained easily if the conformational changes are tightly coupled to changes in the strength of motor-substrate binding.     

Structural components of the arenavirus Pichinde.

Purified Pichinde virions grown in monolayers of BHK-21 cells were found to contain three major species of virion proteins as described previously (Ramos et al., J. Virol. 10:661-667, 1972). Two of the proteins were glycosylated (G1, molecular weight = 64,000; G2, molecular weight = 38,000) and were present in similar proportions on the outer surface of the virions. A third protein (N, molecular weight = 66,000) was not glycosylated and, in association with the viral RNA species, was the major protein component of the viral nucleocapsids. An estimate of the approximate number of molecules of these three major proteins per virion was made. Minor amounts of other proteins were also routinely observed in Pichinde virus preparations. None of the three major protein species were phosphorylated to any significant exten, nor did they contain sulfated components. Two virion RNA species (L and S), but no 18S rRNA species, were detected in Pichinde virus preparations obtained from infected BHK-21 cells.