ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3280377

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The immobilization of drug‐metabolizing enzymes onto polymeric supports offers several advantages over use of conventional microsomal or soluble enzyme preparations. These include increased storage stability, facilitated separation of products from the incubation mixture, the ability to recover and reuse the enzyme catalyst, and in many cases, stabilization of the tertiary structure of membrane‐bound enzymes. Attachment of the protein to the solid support may be accomplished by adsorption, covalent bonding, or entrapment techniques. This methodology has been successfully utilized for studies with such enzymes as cytochrome P‐450, UDPglucuronyltransferases, glutathioneS‐transferases,S‐methyltransferases, andN‐acetyltransferases. Although often employed for the synthesis of xenobiotic metabolites, immobilized enzymes have been used for mechanistic and relative reactivity studies, limited kinetic studies, and extracorporeal detoxification. Coimmobilization of multiple drug‐metabolizing enzyme systems has made possible the sequential formation of metabolites arising from oxidation followed by conjugation. Immobilized enzymes may also be used in the prediction of species‐dependent metabolic pathways. The potential for large‐scale synthesis of drug metabolites using this methodology has been explored.— Dulik, D. M.; Fenselau, C. Use of immobilized enzymes in drug metabolism studies.FASEB J.2: 2235‐2240; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3127263

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Chronic progressive nephropathy is a spontaneous disease common among aging laboratory rats, often making it difficult to distinguish age‐related from drug‐related effects in chronic toxicity studies. Morphological changes of the kidney that occur with age include thickening of glomerular and proximal tubular basement membranes, mesangial proliferation, fusion of foot processes, and, ultimately, glomerular sclerosis. Proteinuria (specifically, albuminuria) is the most striking characteristic change in renal function of aging rats and, generally, correlates well with the severity of age‐related glomerular pathology. Changes in tubular functions also may occur with aging but have not been investigated sufficiently. The pathogenesis of chronic progressive nephropathy is not known; however, hemodynamic adaptations after ad libitum consumption of protein‐rich diets may be a contributing factor. High‐protein diets increase glomerular pressures and flows, perhaps facilitating excretion of metabolic end products. These hemodynamic adaptations may impair the permselective properties of the glomerulus, leading to: enhanced accumulation of macromolecules in the mesangium, progressive mesangial expansion, and, ultimately, glomerular sclerosis. Indeed, decreasing total food or protein intake retards or prevents the progression of age‐related nephropathy. Inasmuch as chronic toxicity studies are complicated by a high incidence of spontaneous nephropathy, implementation of a restricted dietary regimen may improve detection of drug‐induced toxicity.—Goldstein, R. S.; Tarloff, J. B.; Hook, J. B. Age‐related nephropathy in laboratory rats.FASEB J.2: 2241‐2251; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3280378

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

A symposium at the FASEB meeting in Las Vegas in May 1988 will be devoted to the role of cofactors (vitamins, coenzymes, prosthetic groups) in and as posttranslational protein modifications; the symposium is part of a thematic focus on metabolic regulation. In planning the symposium, we decided to consider metabolic regulation in its broadest context, which should include both the short‐term activity modulations in the life of contemporary organisms and the adaptations of special molecular strategies over evolutionary time. We further decided to focus the symposium context on the involvement of cofactors both as catalytic partipicantsinandassubstrates or end products of posttranslational modifications. As a preview of the actual symposium, the present discussion is an attempt to enumerate cases of cofactor involvement in these different categories:1) essential nutrients as participants in posttranslational modifications;2) cofactors as donor substrates in reversible, regulatory modifications; and3) cofactor incorporation or generation as covalent constituents of proteins. The actual symposium topics are taken from category1: vitamin C and protein hydroxylation (K. I. Karivikkio) and vitamin K and protein carboxylation (J. W. Suttie) and category3:biotinylation (H. G. Wood), phycobiliproteins (A. Glazer), and pyruvoyl enzymes (W. Dowhan).— Rucker, R. B.; Wold, F. Cofactors in and as posttranslational protein modifications.FASEB J.2: 2252‐2261; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3127264

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Human urine contains a hitherto unrecognized heparin‐dependent inhibitor of activated protein C (APC) (Mr~ 50,000) that coelutes from heparin‐Sepharose together with the only observed peak of urokinase inhibitory activity at a position (0.35mNaCl) similar to that of plasma protein C (PC) inhibitor. Based on functional assays and immunoblot studies, urokinase and APC compete for this crude inhibitor in the absence or presence of heparin. These results suggest that the same heparin‐dependent urinary inhibitor that is immunologically different from several known protease inhibitors is responsible for the observed inhibition of APC and urokinase. In the absence of heparin this inhibitor inhibits APC and urokinase with similar rates, and heparin enhances its inhibitory activity toward both enzymes with more pronounced stimulation of its PC inhibitory activity than its urokinase inhibitory acitivity. Half‐maximal stimulation of inhibition of APC occurs at about 2 mU/ml and maximal stimulation (~ 10‐fold increase of the pseudo‐first‐order rate constant) at ≥ 50 mU/ml of heparin. This is the first demonstration of competition between APC and urokinase for a heparin‐dependent inhibitor. These results may therefore represent a new link between the two major antithrombotic pathways, the PC pathway and the fibrinolytic system.—Geiger, M.; Heeb, M. J.; Binder, B. R.; Griffin, J. H. Competition of activated protein C and urokinase for a heparin‐dependent inhibitor.FASEB J.2: 2263‐2267; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3350241

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

We hypothesized that an individual's state of health affects its response to stress.Totest this, we used the natural history of inherited heart disease in hamsters as a sliding scale of organ vulnerability on which we superimposed a constant set of stressors. When the animal was stressed at an early point in its disease, heart failure did not develop. Later, after cardiac compensatory changes had developed, stress precipitated overt heart failure. Finally, stress administered when the animal was in overt heart failure further amplified the medical consequences of stress, and some animals succumbed.—Tapp, W. N.; Natelson, B. H. Consequences of stress: a multiplicative function of health status.FASEB J.2: 2268‐2271; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3350242

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Rat alveolar macrophages secrete a growth factor that renders rat lung fibroblasts competent to initiate DNA synthesis in vitro in the presence of platelet‐poor plasma. This biological activity resembles that of platelet‐derived growth factor (PDGF). After separation from putative associated binding proteins by chromatography under acidic conditions, the macrophage‐derived factor exhibited a relative molecular weight similar to that of highly purified human PDGF. The factor bound to a monospecific antibody to human PDGF and thus could be quantitated in an enzyme immunoassay for PDGF. It competed with radiolabeled human PDGF for receptor sites for PDGF on rat lung fibroblasts, and binding to these receptor sites could be specifically inhibited by anti‐PDGF. These data strongly support the view that the factor derived from rat alveolar macrophages is homologous to human PDGF and is similar to human macrophage‐derived PDGF‐like growth factor. Furthermore, we have demonstrated that the lung contains both an effector cell (pulmonary macrophage) and a potential target cell (interstitial fibroblast) for this cytokine. Therefore the rat appears to be an appropriate animal model in which to study macrophage‐derived PDGF‐like growth factors as mediators of proliferation in pulmonary fibrogenesis.— Kumar, R. K.; Bennett, R. A.; Brody, A. R. A homologue of platelet‐derived growth factor produced by rat alveolar macrophages.FASEB J.2: 2272‐2277; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3280379

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

A marked increase in cellular ATP consumption was induced by verapamil in the multidrug‐resistant (MDR) cell line 2780ad, but not in the drug‐sensitive parental cell line A2780. A group of structurally unrelated drugs in concentrations known to reverse MDR, but not the verapamil analog tiapamil, a weak modulator of MDR, had similar effects. This effect was saturated at verapamil concentrations of about 1 μM.These data demonstrate that verapamil concentrations in MDR cells are maintained at a low level at the expense of ATP hydrolysis, and provide a first indication of the amount of metabolic energy used in this process.— Broxterman, H. J.; Pinedo, H. M.; Kuiper, C. M.; Kaptein, L. C. M.; Schuurhuis, G. J.; Lankelma,j. Induction by verapamil of a rapid increase in ATP consumption in multidrug‐resistant tumor cells.FASEB J.2: 2278‐2282; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3350243

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The neural control system for generation of locomotion is an important system for analysis of neural mechanisms underlying complex motor acts. In these studies, a novel experimental model using neonatal rat brain stem and spinal cord in vitro was developed for investigation of the locomotor system in mammals. The in vitro brain stem and spinal cord system was shown to retain functional circuitry for locomotor command generation, motor pattern generation, and sensorimotor integration. This system was exploited to investigate neurochemical mechanisms involved in neurogenesis of locomotion. Evidence was obtained for peptidergic and γ‐aminobutyric acid‐mediated mechanisms in brain‐stem circuits generating locomotor commands. Cholinergic, dopaminergic, and excitatory amino acid‐mediated mechanisms were shown to activate spinal cord circuits for locomotor pattern generation. EndogenousN‐methyl‐d‐aspartic acid receptors in spinal networks were found to play a central role in the generation of locomotion. The chemically induced patterns of motor activity and rhythmic membrane potential oscillations of spinal motoneurons were characteristic of those during locomotion in other mammals in vivo. The in vitro brain stem and spinal cord model provides a versatile and powerful experimental system with potentially broad application for investigation of diverse aspects of the neurobiology of mammalian motor control systems.— Smith, J. C.; Feldman, J. L.; Schmidt, B.J. Neural mechanisms generating locomotion studied in mammalian brain stem‐spinal cord in vitro.FASEB J.2: 2283‐2288; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.2450802

出版商:Wiley    

年代:1988

数据来源: WILEY

ISSN:0892-6638    

DOI:10.1096/fasebj.2.7.3350244

出版商:Wiley    

年代:1988

数据来源: WILEY