Biomedical subjects

J T Horng

Publications and source records attributed to J T Horng.

8 recordsLinked to original sources

PubMed2001

Optical coating designs using the family competition evolutionary algorithm.

A robust evolutionary approach, called the Family Competition Evolutionary Algorithm (FCEA), is described for the synthesis of optical thin-film designs. Based on family competition and adaptive rules, the proposed approach consists of global and local strategies by integrating decreasing mutations and self-adaptive mutations. The method is applied to three different optical coating designs with complex spectral quantities. Numerical results indicate that the proposed approach performs very robustly and is very competitive with other approaches.

Algorithms↗

PubMed2000

A genetic algorithm with adaptive mutations and family competition for training neural networks.

In this paper, we present a new evolutionary technique to train three general neural networks. Based on family competition principles and adaptive rules, the proposed approach integrates decreasing-based mutations and self-adaptive mutations to collaborate with each other. Different mutations act as global and local strategies respectively to balance the trade-off between solution quality and convergence speed. Our algorithm is then applied to three different task domains: Boolean functions, regular language recognition, and artificial ant problems. Experimental results indicate that the proposed algorithm is very competitive with comparable evolutionary algorithms. We also discuss the search power of our proposed approach.

Algorithms↗

PubMed1998

A function for the AP3 coat complex in synaptic vesicle formation from endosomes.

Synaptic vesicles can be coated in vitro in a reaction that is ARF-, ATP-, and temperature-dependent and requires synaptic vesicle membrane proteins. The coat is largely made up of the heterotetrameric complex, adaptor protein 3, recently implicated in Golgi-to-vacuole traffic in yeast. Depletion of AP3 from brain cytosol inhibits small vesicle formation from PC12 endosomes in vitro. Budding from washed membranes can be reconstituted with purified AP3 and recombinant ARF1. We conclude that AP3 coating is involved in at least one pathway of small vesicle formation from endosomes.

ADP-Ribosylation Factor 1↗

PubMed1998

Reconstitution of synaptic vesicle biogenesis from PC12 cell membranes.

Neuroendocrine PC12 cells contain small microvesicles that closely resemble synaptic vesicles in their physical and chemical properties. Two defining characteristics of synaptic vesicles are their homogeneous size and their unique protein composition. Since synaptic vesicles arise by endocytosis from the plasma membrane, nerve terminals and PC12 cells must contain the molecular machinery to sort synaptic vesicles from other membrane proteins and pinch off vesicles of the correct diameter from a precursor compartment. A cell-free reconstitution system was developed that generates vesicles from PC12 membrane precursors in the presence of ATP and brain cytosol and is temperature dependent. At 15 degrees C, surface-labeled synaptic vesicle proteins accumulate in a donor compartment, while labeled synaptic vesicles cannot be detected. The block of synaptic vesicle formation at 15 degrees C enables the use of the monoclonal antibody, KT3, a specific marker for the epitope-tagged synaptic vesicle protein, VAMP-TAg, to label precursors in the synaptic vesicle biogenesis pathway. From membranes labeled in vivo at 15 degrees C, vesicles generated in vitro at 37 degreesC had the sedimentation characteristics of neuroendocrine synaptic vesicles on glycerol velocity gradients, and excluded the transferrin receptor. Therefore, vesiculation and sorting can be studied in this cell-free system.

Adenosine Triphosphate↗

PubMed1998

A v-SNARE participates in synaptic vesicle formation mediated by the AP3 adaptor complex.

Reconstitution of synaptic vesicle formation in vitro has revealed a pathway of synaptic vesicle biogenesis from endosomes that requires the heterotetrameric adaptor complex AP3. Because synaptic vesicles have a distinct protein composition, the AP3 complex should selectively recognize some or all of the synaptic vesicle proteins. Here we show that one element of this recognition process is the v-SNARE, VAMP-2, because tetanus toxin, which cleaves VAMP-2, inhibited the formation of synaptic vesicles and their coating with AP3 in vitro. Mutant tetanus toxin and botulinum toxins, which cleave t-SNAREs, did not inhibit synaptic vesicle production. AP3-containing complexes isolated from coated vesicles could be immunoprecipitated by a VAMP-2 antibody. These data imply that AP3 recognizes a component of the fusion machinery, which may prevent the production of inert synaptic vesicles.

Adaptor Protein Complex 3↗

PubMed1998

NADPH is a specific inhibitor of protein import into glyoxysomes.

We have studied the import of proteins into glyoxysomes in vitro and show that this process is specifically inhibited by NADPH. NADPH affects both binding and translocation of proteins into glyoxysomes, and inhibition is determined by the ratio of NADP+ to NADPH. The site of action of NADPH is most likely within the glyoxysome because (1) pretreatment of glyoxysomes with NADPH, followed by re-isolation of the organelles prior to the import assay, resulted in inhibition of import that could be restored by the addition of NADP+; (2) low concentrations of NADPH inhibited binding of proteins to broken glyoxysome membranes. The sensitivity of protein import to inhibition by NADPH declines as glyoxysomes are converted to leaf-type peroxisomes. A model is proposed that speculates on a possible role for NADPH in regulating protein import into plant peroxisomes.

Alcohol Oxidoreductases↗

PubMed1997

ADP ribosylation factor 1 is required for synaptic vesicle budding in PC12 cells.

Carrier vesicle generation from donor membranes typically progresses through a GTP-dependent recruitment of coats to membranes. Here we explore the role of ADP ribosylation factor (ARF) 1, one of the GTP-binding proteins that recruit coats, in the production of neuroendocrine synaptic vesicles (SVs) from PC12 cell membranes. Brefeldin A (BFA) strongly and reversibly inhibited SV formation in vivo in three different PC12 cell lines expressing vesicle-associated membrane protein-T Antigen derivatives. Other membrane traffic events remained unaffected by the drug, and the BFA effects were not mimicked by drugs known to interfere with formation of other classes of vesicles. The involvement of ARF proteins in the budding of SVs was addressed in a cell-free reconstitution system (Desnos, C., L. Clift-O'Grady, and R.B. Kelly. 1995. J. Cell Biol. 130:1041-1049). A peptide spanning the effector domain of human ARF1 (2-17) and recombinant ARF1 mutated in its GTPase activity, both inhibited the formation of SVs of the correct size. During in vitro incubation in the presence of the mutant ARFs, the labeled precursor membranes acquired different densities, suggesting that the two ARF mutations block at different biosynthetic steps. Cell-free SV formation in the presence of a high molecular weight, ARF-depleted fraction from brain cytosol was significantly enhanced by the addition of recombinant myristoylated native ARF1. Thus, the generation of SVs from PC12 cell membranes requires ARF and uses its GTPase activity, probably to regulate coating phenomena.

ADP-Ribosylation Factor 1↗

PubMed1995

Investigation of the energy requirement and targeting signal for the import of glycolate oxidase into glyoxysomes.

The uptake of glycolate oxidase into peroxisomes has been studied using an in vitro import system. Import of glycolate oxidase was found to be ATP-dependent and temperature-dependent and specific for glyoxysomes. In these respects it resembles the import of isocitrate lyase into both glyoxysomes and leaf-type peroxisomes; thus the ATP-dependence and temperature dependence appear to be general properties of plant microbody protein import. Two mutant versions of glycolate oxidase were prepared lacking 59 amino acids of the N-terminus and 53 amino acids of C-terminus, respectively. Both were capable of ATP-dependent import, whereas a fusion protein consisting of the cytosolic protein dihydrofolate reductase linked to the last 20 amino acids of glycolate oxidase bound to glyoxysomes but did not enter the organelle.

Adenosine Triphosphate↗