Texas Medical Center

About: Texas Medical Center is a healthcare organization based out in Houston, Texas, United States. It is known for research contribution in the topics: Population & Cancer. The organization has 2845 authors who have published 2394 publications receiving 79426 citations.

Qualitative behavior of spontaneous potentials from explants of 15 day chick embryo telencephalon in vitro.

Abstract: The apparatus and technique used in the preparation and observation of explants of brain tissue capable of producing spontaneous potentials in vitro are described. The magnitude and pattern of spontaneous potentials from explants of telencephalon of 15 day chick embryos (measured using external bare platinum electrodes) and some aspects of their "normal" behavior during 12 days in vitro are also described. No change was noted in these potentials with change of amplifiers, recorders, or electrodes. The response of the potentials to change in temperature and proportionate composition of the atmosphere around the explant was such as to suggest that the potentials arise as a result of a living process. The changes brought about by the administration of anesthetics, strychnine, brucine, and barbiturates were those that might be anticipated in a normal functional activity of the central nervous system. It is concluded that these potentials are a true physiological phenomenon and arise from living cells of the central nervous system.

Studies on the Primary Structure of Apolipoprotein B

Abstract: Recent years have seen considerable accumulation of physical-chemical and functional data concerning the low-density lipoproteins (LDL) . Elegant studies designed to demonstrate core regions of cholesteryl esters which perform cooperative phase transitions have been well-documented.1-3 Low angle xray and neutron scattering experiments suggest a quasispherical structure with protein and polar lipids surrounding a nonpolar lipid core. Functionally LDL interacts with a variety of cells by a high-affinity receptor, presumably to the protein, which initiates a series of events all aimed at cellular control of cholesterol synthesis.' Such intensity of interest about the LDL particle has been justified by the epidemiological suggestion that it is directly involved in the atherogenic process.8 In spite of all that has been documented concerning the structure and function of low-density lipoproteins, the characterization of perhaps its most important component, that of the apoprotein, remains uniquely obscure. Handling of the apoprotein has proven a test (of abilities and patience) to anyone who has attempted it. If one has not worked with the apoprotein of LDL, it is difficult to understand all the fuss over it. That this protein presents a unique chemical problem is apparent by the fact that, although for many years apolipoprotein B (apoB) has been an intensely studied moiety, and large quantities are readily available, very little is confidently known about the apolipoprotein. In our attempts to obtain primary sequence data on the apoprotein, we have continually struggled with the solubility and aggregation problems associated not only with the protein but also with fragments of apoB. Some of the problems with the cyanogen bromide peptides have been discussed by us and l1 In the following report, we outline our recent approaches to obtaining chemical and sequence information on apoB. Because of the difficulties involved in working with both the apoprotein and its fragments, we emphasize some of the problems that we have encountered in the hope that our experiences will be of aid to others. The bulk of data presented here will concern the initial attempts to isolate, purify, and characterize the peptides generated from intact LDL by tryptic digestion. We will demonstrate that enumerable purification steps were often necessary, leading to overall low yields. We also suggest that several peptides are from partial cleavages, probably leading

Ubiquitin-dependent and -independent proteasomal degradation of apoB associated with endoplasmic reticulum and Golgi apparatus, respectively, in HepG2 cells.

Abstract: Studies in hepatocyte cultures indicate that apolipoprotein (apo) B-100 production is regulated largely by intracellular degradation and the proteasome pathway is a major mechanism for the degradation. In the present study, we have examined the detailed itinerary of apoB degradation through its secretory pathway in HepG2 cells. We found that ubiquitin-dependent proteasomal degradation of apoB largely occurred on the cytosolic surface of rough and smooth endoplasmic reticulum (ER) and that a small proportion of apoB was dislodged from the secretory organelles into the cytosolic compartment where it underwent ubiquitination for proteasomal degradation. The transmembrane conformation of apoB persisted as the protein was transported through the Golgi apparatus. We further demonstrated that proteasomal degradation of apoB was associated the Golgi apparatus but Golgi-associated apoB was not ubiquitinated, indicating an ubiquitin-independent proteasomal degradation of apoB is associated with this organelle. We conclude that apoB undergoes proteasomal degradation while going through different compartments of the secretory pathway; further, ER-associated proteasomal degradation of apoB in the ER is ubiquitin-dependent whereas that occurring in the Golgi is ubiquitin-independent.