Dynamics of morphological changes for mitochondrial fission and fusion

Mitochondria experience continuous fusion and fission in a living cell, but their dynamics remains poorly quantified. Here a theoretical model was developed, upon a simplified population balance equation (PBE), to predict the morphological changes induced by mitochondrial fission and fusion. Assuming that both fission and fusion events are statistically independent, the survival probability of mitochondria staying in the fission or fusion state was formulated as an exponentially-decayed function with time, which depended on the time-dependent distribution of the mitochondrial volume and the fission and fusion rates. Parametric analysis was done for two typical volume distributions. One was Gamma distribution and the other was Gaussian distribution, derived from the measurements of volume distribution for individual mitochondria in a living cell and purified mitochondria in vitro. The predictions indicated that the survival probability strongly depended on morphological changes of individual mitochondria and was inversely correlated to the fission and fusion rates. This work provided a new insight into quantifying the mitochondrial dynamics via monitoring the evolution of the mitochondrial volume.

beta-delayed fission of Ac-228

The basic process of an exotic decay mode namely P-delayed fission is simply introduced. The progress status of the study in the world is essentialized. The observation of P-delayed fission of Ac-228 is reported. The radium was radiochemically separated from natural thorium. Thin Ra sources in which Ac-228 was got through Ra-228 ->(beta-) Ac-228 were prepared for observing fission fragments from beta-delayed fission Ac-228. They exposed to the mica fission track detectors, and measured by an HPGe gamma-ray detector. The beta-delayed fission events of Ac-228 were observed and its beta-delayed fission probability was found to be (5 +/- 2) x 10(-12).

Search for beta-delayed fission of Ac-228

Radium was radiochemically separated from natural thorium. Thin Ra-228 ->beta Ac-228 sources were prepared and exposed to mica fission track detectors, and measured by an HPGe gamma-ray detector. The beta-delayed fission events of Ac-228 were observed and its beta-delayed fission probability was found to be (5 +/- 2)x10(-12).

Unified fission model for proton emission

The unified fission model (UFM) combining with the phenomenological assault frequency has been carried out to investigate the proton-radioactivity half-lives of spherical proton emitters. The results are in good agreement with the experimental data and other theoretical values, and newly observed spherical proton emitters have been analyzed. Finally, the effect of angular momentum transfer on half-life of proton emission has been discussed in detail and a formula can be used to describe this relationship.

Improvement of a Fission-Like Model for Nuclear alpha Decay

The alpha decay constant is the product of the penetrability P and assault frequency nu(0) in the fission-like model. An effective assault frequency P-nu replacing the previous assault frequency nu(0) is introduced for improvement of a fission-like model named the generalized liquid drop model (GLDM) to describe the nuclear alpha decay process more accurately. Two analytical formulae are proposed for the effective assault frequency due to experimental data within the GLDM. The improved model can be used to give accurate calculations for alpha decay half-lives.

Fission dynamics for capture reactions in 58,64ni + 208pb systems: New results in terms of thermal energy and neutron multiplicity correlated distributions

The neutron multidetector DéMoN has been used to investigate the symmetric splitting dynamics in the reactions 58.64Ni + 208Pb with excitation energies ranging from 65 to 186 MeV for the composite system. An analysis based on the new backtracing technique has been applied on the neutron data to determine the two-dimensional correlations between the parent composite system initial thermal energy (EthCN) and the total neutron multiplicity (νtot), and between pre- and post-scission neutron multiplicities (νpre and νpost, respectively). The νpre distribution shape indicates the possible coexistence of fast-fission and fusion-fission for the system 58Ni + 208Pb (Ebeam = 8.86 A MeV). The analysis of the neutron multiplicities in the framework of the combined dynamical statistical model (CDSM) gives a reduced friction coefficient β = 23 ± 2512 × 1021 s-1, above the one-body dissipation limit. The corresponding fission time is τf = 40 ± 4620 × 10-21 s. © 1999 Elsevier Science B.V. All rights reserved.

Arp2p, a potential substrate for NatB acetyltransferase in fission yeast, is important in actin patch nucleation and motility in arp2-1 and arm1 ts mutants

The actin cytoskeleton is a dynamic and complex structure in fission yeast that plays a major function in many cell processes including cellular growth, septa formation, endocytosis and cellular division. Computational studies have shown that Arp2p, which forms part of the Arp2/3 complex, is a potential substrate of NatB acetyltransferase which has specificity for proteins possessing an N-terminal Met-Asp or Met-Glu sequence motif. In arm1- mutants the loss of function of Arm1p, an auxillary subunit required for NatB activity, results in a temperature sensitive phenotype characterized by multiple septa, failure of endocytosis, and the inability to form actin cables. A temperature sensitive mutant of Schizosaccharomyces pombe arp2 gene exhibits a similar phenotype as seen by the formation of improper septa, slow growth, and the delocalization of actin patches. Four expression vectors encoding the open reading frames of arp2 and cdc8 (tropomyosin) were constructed with a modification changing the second residue to a Histidine, believed to mimic the charge distribution of natural acetylation by NatB. Constructs tested in normal yeast strains remained viable and grew normally in the presence of Met-His Arp2p and tropomyosin. Analysis of their ability to suppress the mutant phenotypes of arp2-1 and arm1- mutants is an area of research to be explored in future studies.