摘要:

Multiple pathways of intracellular protein breakdown operate within cells, and the activities of different pathways can be regulated under different physiological conditions. Recent studies suggest that molecular determinants within proteins target them for different pathways of proteolysis. Proteins that are partially unfolded and have an unblocked amino‐terminal amino acid with a bulky side chain appear to be good substrates for cytosolic, ubiquitin‐mediated pathways of proteolysis. Certain modifications of internal residues such as oxidation of methionines also increase the susceptibility of certain proteins to ubiquitin‐mediated proteolysis. Rapidly degraded normal proteins contain peptide regions rich in proline, glutamate, serine, and threonine (PEST regions). The pathway of degradation for these proteins has not been established, but they may be good substrates for calcium‐activated proteases. In addition, a lysosomal pathway of protein degradation is activated when serum is withdrawn from cultured cells and is selective for cytosolic proteins containing peptide regions similar to Lys‐Phe‐Glu‐Arg‐Gln (KFERQ). This short review summarizes our current understanding of mechanisms of protein breakdown in eukaryotes and evaluates potential molecular determinants of protein half‐lives.— Dice, J. F. Molecular determinants of protein half‐lives in eukaryotic cells.FASEB J.1: 349‐357; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.2824267

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Oxidant species such as superoxide radical (O2˙‐), hydrogen peroxide (H2O2), hydroxyl radical (HO.), and lipid peroxides (LOOH) are becoming increasingly implicated in human disease. However, the question of whether such oxidants are a major cause of tissue injury in human disease or are merely produced during such injury has been difficult to answer because of inadequate experimental techniques, and possibly because of an overemphasis on lipid peroxidation as a mechanism of oxidant injury. Recent developments in methodology, in our understanding of the primary mechanism of oxidant toxicity to cells, and in concepts of antioxidant protection are reviewed. Good evidence now exists for some role of oxidant damage to tissues in the pathology of several human diseases, including rheumatoid arthritis, reperfusion injury, immune injury to lung and kidney, and cerebral trauma or ischemia. These have led to promising suggestions for new therapeutic approaches.— Halliwell, B. Oxidants and human disease: some new concepts.FASEB J.1: 358‐364; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.2824268

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Many types of data are best analyzed by fitting a curve using nonlinear regression, and computer programs that perform these calculations are readily available. Like every scientific technique, however, a nonlinear regression program can produce misleading results when used inappropriately. This article reviews the use of nonlinear regression in a practical and nonmathematical manner to answer the following questions: Why is nonlinear regression superior to linear regression of transformed data? How does nonlinear regression differ from polynomial regression and cubic spline? How do nonlinear regression programs work? What choices must an investigator make before performing nonlinear regression? What do the final results mean? How can two sets of data or two fits to one set of data be compared? What problems can cause the results to be wrong? This review is designed to demystify nonlinear regression so that both its power and its limitations will be appreciated.— Motulsky, H. J.; Ransnas, L. A. Fitting curves to data using nonlinear regression: a practical and nonmathematical review.FASEB J.1: 365‐374; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.3315805

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

In contrast to the widespread ability of bacteria, plants, and animals to incorporate selenium nonspecifically into proteins in the form of selenomethionine residues, the selenoamino∗∗∗ acid selenocysteine occurs as a highly specific component of a few selenium‐dependent enzymes. Selenocysteine has been identified in glycine reductase, formate dehydrogenase, and hydrogenase of bacterial origin and glutathione peroxidase from mammalian and avian sources. In these enzymes there is evidence that the selenol group, which is largely ionized at physiological pH, functions as a redox center. It now seems clear, from studies with both prokaryotes and eukaryotes, that the UGA opal stop codon is used to specify the cotranslational insertion of selenocysteine into proteins. The factors that allow this unusual use of the stop codon are, however, unknown. The occurrence of selenium as a normal constituent of several bacterial tRNA species has been established. The presence of a selenonucleoside, 5‐methylaminomethyl‐2‐selenouridine, in the first or wobble position of the anticodons of certain glutamate and lysine iso‐acceptor species influences codon‐anticodon interaction and thus may serve to regulate translational processes. The biosynthesis of the selenonucleoside appears to involve the ATP‐dependent activation of the sulfur in a preformed 5‐methylaminomethyl‐2‐thiouridine residue in tRNA and replacement of the sulfur with selenium.— Stadtman, T. C. Specific occurrence of selenium in enzymes and amino acid tRNAs.FASEB J.1: 375‐379; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.2445614

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

β‐Adrenergic agonist‐stimulated hyperpolarization, whole‐cell cAMP accumulation, and activity of isoproterenol‐stimulated membrane‐bound adenylate cyclase (EC 4.6.1.1) inXenopus laevisovarian oocytes are entirely dependent on the presence of nascent follicle cells. A method was developed to remove rapidly and completely all extra‐oocyte cell types to yield defolliculated oocytes that exhibited normal viability and resting membrane potentials yet lacked β‐adrenergic receptor (βAR)‐stimulated responses. Purified follicle membranes contained βAR‐stimulated adenylate cyclase activity, whereas oocyte cell membranes did not. Purified oocyte membrane preparations fromX. laevisoocytes previously microinjected with C6‐2B rat astrocytoma mRNA, and subsequently defolliculated, exhibited novel βAR and forskolin‐stimulated adenylate cyclase activity. These experiments demonstrate that oocytes expressed rat C6‐2B mRNA coding for the β‐adrenergic receptor and the components necessary for forskolin‐stimulated adenylate cyclase activity.— Smith, A. A.; Brooker, T.; Brooker, G. Expression of rat mRNA coding for hormone‐stimulated adenylate cyclase inXenopusoocytes.FASEB J.1: 380‐387; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.2824269

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Inositol 1,4,5‐trisphosphate (Ins‐1,4,5‐P3) is an important second‐messenger molecule that mobilizes Ca2+from intracellular stores in response to the occupancy of receptor by various Ca2+‐mobilizing agonists. The fate of Ins‐1,4,5‐P3is determined by two enzymes, a 3‐kinase and a 5‐phosphomonoesterase. The first enzyme converts Ins‐1,4,5‐P3to Ins‐1,3,4,5‐P4, whereas the latter forms Ins‐1,4‐P2. Recent studies suggest that Ins‐1,3,4,5‐P4might modulate the entry of Ca2+from an extracellular source. In the current report, we describe the partial purification of the 3‐kinase [ ~ 400‐fold purified, specific activity = 0.12 μmol/(min · mg)] from the cytosolic fraction of bovine brain and studies of its catalytic properties. We found that the 3‐kinase activity is significantly activated by the Ca2+/calmodulin complex. Therefore, we propose that Ca2+mobilized from endoplasmic reticulum by the action of Ins‐1,4,5‐P3forms a complex with calmodulin, and that the Ca2+/calmodulin complex stimulates the conversion of Ins‐1,4,5‐P3, an intracellular Ca2+mobilizer, to Ins‐1,3,4,5‐P4, an extracellular Ca2+mobilizer. A rapid assay method for the 3‐kinase was developed that is based on the separation of [3‐32P]Ins‐1,3,4,5‐P4and [γ‐32P]ATP by thin‐layer chromatography. Using this new assay method, we evaluated kinetic parameters (Kmfor ATP = 40 μm,Kmfor Ins‐1,4,5‐P3= 0.7 μm,Kifor ADP ‐ 12 μm) and divalent cation specificity (Mg2+>>Mn2+>Ca2+) for the 3‐kinase. Studies with various inositol polyphosphates indicate that the substrate‐binding site is quite specific to Ins‐1,4,5‐P3. Nevertheless, Ins‐2,4,5‐P3could be phosphorylated at a velocity approximately 1/20‐1/30 that of Ins‐1,4,5‐P3.—Ryu, S. H.; Lee, S. Y.; Lee, K.‐Y.; Rhee, S. G. Catalytic properties of inositol trisphosphate kinase: activation by Ca2+and calmodulin.FASEB J.1: 388‐393; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.2824270

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

A study was done to examine the effects of aluminum, magnesium, and boron on major mineral metabolism in postmenopausal women. This communication describes some of the effects of dietary boron on 12 women between the ages of 48 and 82 housed in a metabolic unit. A boron supplement of 3 mg/day markedly affected several indices of mineral metabolism of seven women consuming a low‐magnesium diet and five women consuming a diet adequate in magnesium; the women had consumed a conventional diet supplying about 0.25 mg boron/day for 119 days. Boron supplementation markedly reduced the urinary excretion of calcium and magnesium; the depression seemed more marked when dietary magnesium was low. Boron supplementation depressed the urinary excretion of phosphorus by the low‐magnesium, but not by the adequate‐magnesium, women. Boron supplementation markedly elevated the serum concentrations of 17β‐estradiol and testosterone; the elevation seemed more marked when dietary magnesium was low. Neither high dietary aluminum (1000 mg/day) nor an interaction between boron and aluminum affected the variables presented. The findings suggest that supplementation of a low‐boron diet with an amount of boron commonly found in diets high in fruits and vegetables induces changes in postmenopausal women consistent with the prevention of calcium loss and bone demineralization.— Nielsen, F. H.; Hunt, C. D.; Mullen, L. M.; Hunt, J. R. Effect of dietary boron on mineral, estrogen, and testosterone metabolism in postmenopausal women.FASEB J.1: 394‐397; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.3678698

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

Human fibroblast cell cultures were employed as a model system to rapidly examine several potentially important variables involved in the use of high‐voltage, pulsed galvanic stimulation (HVPGS) to increase the healing rate of soft tissue injuries. Fibroblasts were grown on Millipore filters and exposed to HVPGS of various voltages and pulse rates for 20 min in a rectangular, plastic chamber filled with growth medium. Filters with attached cells were placed either in the center of the chamber or close to the positive or negative electrode. Protein synthesis and DNA synthesis were monitored after stimulation using the radioactively labeled precursors, [3H]proline and [3H]thymidine, respectively. The major results obtained in this study are as follows:1) the rates of both protein and DNA synthesis can be significantly increased by specific combinations of HVPGS voltage and pulse rate;2) maximum stimulation of protein and DNA synthesis was obtained at 50 and 75 V, respectively, with a pulse rate of 100 pulses/s and the cells located near the negative electrode; and3) exposure to HVPGS intensities greater than 250 V (at all pulse rates and locations within the chamber) is inhibitory for both protein and DNA synthesis. In view of the results obtained in preliminary clinical studies on the use of HVPGS for the treatment of dermal ulcers, it appears that similar voltages, pulse rates, and relative electrode location may be required for maximum acceleration of human skin wound healing.— Bourguignon, G. J.; Bourguignon, L. Y. W. Electric stimulation of protein and DNA synthesis in human fibroblasts.FASEB J.1: 398‐402; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.3678699

出版商:Wiley    

年代:1987

数据来源: WILEY

摘要:

We have developed a model of isochemic bowel necrosis in the rat by injecting platelet‐activating factor (PAF) or PAF in combination with bacterial endotoxin. PAF causes profound hypotension, and it has been suggested that it is released during endotoxin shock. Because ischemic bowel necrosis is often associated with shock or infection, it is possible that PAF is the endogenous mediator that causes shock and bowel necrosis during sepsis. In this study, we have demonstrated that:1) normal intestine contained a small amount of PAF;2) necrotic lesions of the intestine could be induced by endotoxin injection;3) PAF production in the bowel is markedly increased in animals treated with endotoxin;4) pretreatment of the animal with PAF antagonists prevent endotoxin‐induced necrosis;5) isolated, buffer‐perfused small intestine produced a small quantity of PAF in response to endotoxin injection. Therefore, we conclude that PAF is a likely endogenous mediator in endotoxemia, which causes bowel necrosis and shock.—Hsueh, W.; González‐Crussi, F.; Arroyave, J. L. Platelet‐activating factor: an endogenous mediator for bowel necrosis in endotoxemia.FASEB J.1: 403‐405; 1987.

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.3678700

出版商:Wiley    

年代:1987

数据来源: WILEY

ISSN:0892-6638    

DOI:10.1096/fasebj.1.5.3678701

出版商:Wiley    

年代:1987

数据来源: WILEY