Determinants of single photon response variability.

The responses to single photon absorptions (quantum bumps) vary randomly in size in Limulus photoreceptors. This variability is a natural consequence of simple chemical reactions involving a small number of molecules. The measured size distributions differ significantly from the exponential distribution predicted by the simplest transduction cascade models, one feature of which is that light-activated rhodopsin (R*) is turned off in a single step process. As shown in the companion paper, the nonexponential size distributions can be accounted for if R* is turned off in a multi-step process. This would lead to a nonexponential (peaked) distribution in the number of G-protein molecules activated during a quantum bump and to a nonexponential distribution in the size of bumps. To test this possibility we measured the distribution of quantum bump size under two conditions in which the variability in the number of activated G-proteins was eliminated. eliminated. In one method, bumps were produced by direct activation of single G-proteins using GTP-gamma-S; in the second GDP-beta-S reduced the R* gain to the point where most quantal events were due to activation of a single G-protein. In both cases the size distribution of bumps became much closer to an exponential distribution than that of normal light-induced bumps. These results support the idea that the size distribution of light-induced bumps is dependent on events at the R* level and reflects to the multi-step deactivation of R*.

Download Full-text

Elementary response triggered by transducin in retinal rods

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1817781116 ◽

2019 ◽

Vol 116 (11) ◽

pp. 5144-5153 ◽

Cited By ~ 9

Author(s):

Wendy W. S. Yue ◽

Daniel Silverman ◽

Xiaozhi Ren ◽

Rikard Frederiksen ◽

Kazumi Sakai ◽

...

Keyword(s):

G Protein ◽

Single Photon ◽

High Gain ◽

Intact Mouse ◽

Physiological Processes ◽

Retinal Rods ◽

Retinal Rod ◽

Elementary Response ◽

Electrical Effect ◽

Single Photon Response

G protein-coupled receptor (GPCR) signaling is crucial for many physiological processes. A signature of such pathways is high amplification, a concept originating from retinal rod phototransduction, whereby one photoactivated rhodopsin molecule (Rho*) was long reported to activate several hundred transducins (GT*s), each then activating a cGMP-phosphodiesterase catalytic subunit (GT*·PDE*). This high gain at the Rho*-to-GT* step has been challenged more recently, but estimates remain dispersed and rely on some nonintact rod measurements. With two independent approaches, one with an extremely inefficient mutant rhodopsin and the other with WT bleached rhodopsin, which has exceedingly weak constitutive activity in darkness, we obtained an estimate for the electrical effect from a single GT*·PDE* molecular complex in intact mouse rods. Comparing the single-GT*·PDE* effect to the WT single-photon response, both in Gcaps−/− background, gives an effective gain of only ∼12–14 GT*·PDE*s produced per Rho*. Our findings have finally dispelled the entrenched concept of very high gain at the receptor-to-G protein/effector step in GPCR systems.

Download Full-text

Formation and Structure of Casein Micelles in Lactating Mammary Tissue

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100067741 ◽

1970 ◽

Vol 28 ◽

pp. 150-151

Author(s):

Robert J. Carroll ◽

Marvin P. Thompson ◽

Harold M. Farrell

Keyword(s):

Size Distribution ◽

G Protein ◽

Milk Proteins ◽

Mammary Tissue ◽

Colloidal System ◽

Casein Micelles ◽

The Stability

Milk is an unusually stable colloidal system; the stability of this system is due primarily to the formation of micelles by the major milk proteins, the caseins. Numerous models for the structure of casein micelles have been proposed; these models have been formulated on the basis of in vitro studies. Synthetic casein micelles (i.e., those formed by mixing the purified αsl- and k-caseins with Ca2+ in appropriate ratios) are dissimilar to those from freshly-drawn milks in (i) size distribution, (ii) ratio of Ca/P, and (iii) solvation (g. water/g. protein). Evidently, in vivo organization of the caseins into the micellar form occurs in-a manner which is not identical to the in vitro mode of formation.

Download Full-text

Faculty Opinions recommendation of Keeping G proteins at bay: a complex between G protein-coupled receptor kinase 2 and Gbetagamma.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1013646.191521 ◽

2003 ◽

Author(s):

Patricia C Weber

Keyword(s):

G Protein ◽

G Proteins ◽

Receptor Kinase ◽

G Protein Coupled Receptor ◽

G Protein Coupled

Download Full-text

The circulating floating bed reactor: effect of particle size distribution of the carrier on ammonia conversion

Water Science & Technology ◽

10.2166/wst.2000.0471 ◽

2000 ◽

Vol 41 (4-5) ◽

pp. 393-400 ◽

Cited By ~ 5

Author(s):

J.M. Garrido-Fernandez ◽

R. Méndez ◽

J.M. Lema ◽

V. Lazarova

Keyword(s):

Particle Size ◽

Size Distribution ◽

G Protein ◽

Biomass Concentration ◽

Biomass Accumulation ◽

Ammonia Removal ◽

Operating Conditions ◽

Nitrification Rate ◽

Ammonia Conversion ◽

Biomass Activity

Three Circulating Floating Bed Reactors (CFBR) R1, R2 and R3 with 20% v/v of a plastic carrier with different size distribution were operated to study the effect of the particles size of the carrier on biomass accumulation and nitrification performance. Operating conditions were similar in the three systems: ammonia concentrations around 50 mg-N–NH4+/ L, ammonia loading rates up to 1.2 kg N–NH4+/m3·d and temperatures between 14 and 27°C. Accumulation of nitrite was observed until day 65th. This w as result both of the inhibition of nitrite oxidation by free ammonia until day 20th and the insignificant accumulation of a biomass with low nitrite oxidising capacity between days 20 and 65th. Ammonia conversion rate and removal efficiency were higher in the reactor with lower particle size, R3 (nitrification rate of 1.1 kg N–NH4+/m3·d and ammonia removal of 97% at 16°C), than in R2 or R1 (nitrification rate of 1.0 kg N–NH4+/m3·d and ammonia removal of 90% at 16°C). The better efficiency in R3 was obtained as a result of the higher specific surface of the biofilm developed. Biomass activity was similar in the three reactors (2.2 and 1.12 g N/g protein · d at 30 and 15°C, respectively). Both the biomass evolution with time and biomass retention in the systems was practically not influenced by the size of particle. Biomass concentration of 1.2 g protein/L was retained in the carrier and up to 20% of the newly produced biomass was retained in the CFBRs.

Download Full-text

Effect of Strain-Induced Precipitation on the Recrystallization Kinetics in a Model Alloy

Metallurgical and Materials Transactions A ◽

10.1007/s11661-021-06206-8 ◽

2021 ◽

Author(s):

Mo Ji ◽

Martin Strangwood ◽

Claire Davis

Keyword(s):

Grain Size ◽

Size Distribution ◽

Grain Size Distribution ◽

Avrami Exponent ◽

Model Alloy ◽

Size Distributions ◽

Recrystallization Kinetics ◽

Grain Size Distributions ◽

Recrystallized Grain Size ◽

Nb Addition

AbstractThe effects of Nb addition on the recrystallization kinetics and the recrystallized grain size distribution after cold deformation were investigated by using Fe-30Ni and Fe-30Ni-0.044 wt pct Nb steel with comparable starting grain size distributions. The samples were deformed to 0.3 strain at room temperature followed by annealing at 950 °C to 850 °C for various times; the microstructural evolution and the grain size distribution of non- and fully recrystallized samples were characterized, along with the strain-induced precipitates (SIPs) and their size and volume fraction evolution. It was found that Nb addition has little effect on recrystallized grain size distribution, whereas Nb precipitation kinetics (SIP size and number density) affects the recrystallization Avrami exponent depending on the annealing temperature. Faster precipitation coarsening rates at high temperature (950 °C to 900 °C) led to slower recrystallization kinetics but no change on Avrami exponent, despite precipitation occurring before recrystallization. Whereas a slower precipitation coarsening rate at 850 °C gave fine-sized strain-induced precipitates that were effective in reducing the recrystallization Avrami exponent after 50 pct of recrystallization. Both solute drag and precipitation pinning effects have been added onto the JMAK model to account the effect of Nb content on recrystallization Avrami exponent for samples with large grain size distributions.

Download Full-text

Remote sensing of water cloud droplet size distributions using the backscatter glory: a case study

Atmospheric Chemistry and Physics ◽

10.5194/acp-4-1255-2004 ◽

2004 ◽

Vol 4 (5) ◽

pp. 1255-1263 ◽

Cited By ~ 35

Author(s):

B. Mayer ◽

M. Schröder ◽

R. Preusker ◽

L. Schüller

Keyword(s):

Remote Sensing ◽

Size Distribution ◽

Droplet Size ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Single Scattering ◽

Effective Radius ◽

Radiative Properties ◽

High Angular Resolution ◽

Size Distributions

Abstract. Cloud single scattering properties are mainly determined by the effective radius of the droplet size distribution. There are only few exceptions where the shape of the size distribution affects the optical properties, in particular the rainbow and the glory directions of the scattering phase function. Using observations by the Compact Airborne Spectrographic Imager (CASI) in 180° backscatter geometry, we found that high angular resolution aircraft observations of the glory provide unique new information which is not available from traditional remote sensing techniques: Using only one single wavelength, 753nm, we were able to determine not only optical thickness and effective radius, but also the width of the size distribution at cloud top. Applying this novel technique to the ACE-2 CLOUDYCOLUMN experiment, we found that the size distributions were much narrower than usually assumed in radiation calculations which is in agreement with in-situ observations during this campaign. While the shape of the size distribution has only little relevance for the radiative properties of clouds, it is extremely important for understanding their formation and evolution.

Download Full-text

Every Detail Matters. That Is, How the Interaction between Gα Proteins and Membrane Affects Their Function

Membranes ◽

10.3390/membranes11030222 ◽

2021 ◽

Vol 11 (3) ◽

pp. 222

Author(s):

Agnieszka Polit ◽

Paweł Mystek ◽

Ewa Błasiak

Keyword(s):

Signal Transduction ◽

G Protein ◽

G Proteins ◽

Lipid Membranes ◽

Signaling Proteins ◽

Heterotrimeric G Proteins ◽

Membrane Attachment ◽

The Individual ◽

Multicellular Organisms ◽

G Protein Coupled

In highly organized multicellular organisms such as humans, the functions of an individual cell are dependent on signal transduction through G protein-coupled receptors (GPCRs) and subsequently heterotrimeric G proteins. As most of the elements belonging to the signal transduction system are bound to lipid membranes, researchers are showing increasing interest in studying the accompanying protein–lipid interactions, which have been demonstrated to not only provide the environment but also regulate proper and efficient signal transduction. The mode of interaction between the cell membrane and G proteins is well known. Despite this, the recognition mechanisms at the molecular level and how the individual G protein-membrane attachment signals are interrelated in the process of the complex control of membrane targeting of G proteins remain unelucidated. This review focuses on the mechanisms by which mammalian Gα subunits of G proteins interact with lipids and the factors responsible for the specificity of membrane association. We summarize recent data on how these signaling proteins are precisely targeted to a specific site in the membrane region by introducing well-defined modifications as well as through the presence of polybasic regions within these proteins and interactions with other components of the heterocomplex.

Download Full-text

Production, processing and partial purification of functional G protein βγ subunits in baculovirus-infected insect cells

Biochemical Journal ◽

10.1042/bj2860677 ◽

1992 ◽

Vol 286 (3) ◽

pp. 677-680 ◽

Cited By ~ 21

Author(s):

J D Robishaw ◽

V K Kalman ◽

K L Proulx

Keyword(s):

G Protein ◽

G Proteins ◽

Insect Cells ◽

Expression System ◽

Baculovirus Expression System ◽

Partial Purification ◽

Baculovirus Expression ◽

Gamma Subunits ◽

Infected Insect ◽

Beta 2

As a result of the inability to resolve the heterogeneous mixture of G protein beta gamma subunits present in tissues, it has not been possible to compare different beta gamma subunits of the G proteins in terms of their proposed roles in receptor-effector coupling. This study was undertaken to establish the utility of the baculovirus expression system in producing homogeneous beta gamma subunits of defined composition for the comparative analysis of these subunits in reconstitution systems. In this study we report the expression, and appropriate post-translational processing, of recombinant beta 2, gamma 2 and gamma 3 subunits. In addition, we show that the recombinant beta gamma subunits can be readily purified, and can functionally interact with the alpha subunits of the G proteins.

Download Full-text

Factors Influencing the Particle Size Distribution in an Abrasive Waterjet

Journal of Engineering for Industry ◽

10.1115/1.2899714 ◽

1991 ◽

Vol 113 (4) ◽

pp. 402-411 ◽

Cited By ~ 13

Author(s):

T. J. Labus ◽

K. F. Neusen ◽

D. G. Alberts ◽

T. J. Gores

Keyword(s):

Particle Size ◽

Particle Size Distribution ◽

Size Distribution ◽

Cutting Speed ◽

Target Material ◽

Abrasive Waterjet ◽

Sieve Analysis ◽

Size Distributions ◽

Mixing Process ◽

Jet Mixing

A basic investigation of the factors which influence the abrasive jet mixing process was conducted. Particle size analysis was performed on abrasive samples for the “as-received” condition, at the exit of the mixing tube, and after cutting a target material. Grit size distributions were obtained through sieve analysis for both water and air collectors. Two different mixing chamber geometries were evaluated, as well as the effects of pressure, abrasive feed rate, cutting speed, and target material properties on particle size distributions. An analysis of the particle size distribution shows that the main particle breakdown is from 180 microns directly to 63 microns or less, for a nominal 80 grit garnet. This selective breakdown occurs during the cutting process, but not during the mixing process.

Download Full-text