摘要:

The structural features of the heterodimeric glycoprotein hormones (LH, FSH, TSH, and hCG) are briefly reviewed. Removal of carbohydrate chains does not reduce binding of the hormones to membrane receptors, but markedly reduces biological responses. The ∗∗∗glycopeptides from the hormone do not reduce binding of native hormone to receptors but do reduce biological responses. Newer data concerned with replication of different regions of the peptide chains of these molecules using synthetic peptides are reviewed and presented. These studies indicate that two regions on the common α subunit are involved with receptor binding of the LH, hCG, and TSH molecules. These regions are α26 to 46 and α75‐92. Two synthetic disulfide loop peptides from the hCGβ subunit β38‐57 and β93‐100 also block binding of hCG to its receptor. In addition, the β38‐57 peptide stimulates testosterone production by Leydig cells. These data indicate that glycoprotein hormone binding to plasma membrane receptors involves a discontinuous site on the hormone that spans both the α andβsubunits, and that the α subunit sites are similar for several hormones.—Ryan, R. J.; Charlesworth, M. C.; McCormick, D. J.; Milius, R. P.; Keutmann, H. T. The glycoprotein hormones: recent studies of structure‐function relationships.FASEB J.2: 2661‐2669; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.2456242

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

It is now accepted that many hormones and neurotransmitters exert their effects through G protein‐mediated activation of a phospholipase C, which breaks down phosphatidylinositol bisphosphate. This releases inositol trisphosphate, which mobilizes intracellular calcium, and diacylglycerol, which, in turn, activates protein kinase C. However, recent evidence indicates that other mechanisms are involved. In some cells, the increases in cytosolic calcium elicited within 1‐2 s by high concentrations of agonists or at later times by low, physiological concentrations of agonists occur without any detectable changes in inositol phosphates and calcium mobilization, and result from the opening of plasma membrane channels that are permeable to Ca2+. This response appears to be mediated more directly by G proteins. These findings question the postulated roles of inositol phosphates and calcium mobilization in the stimulation of calcium influx. Measurements of the mass and fatty acid composition of the inositol phospholipids and of the diacylglycerol and phosphatidic acid generated by agonists in several cell types indicate that phosphatidylinositol bisphosphate is probably a minor source of these lipids. On the other hand, measurements of phosphatidylcholine, choline, and phosphocholine indicate that this phospholipid is a major source, and that its breakdown involves both phospholipase C and D. These findings indicate that phosphatidylcholine breakdown may be more important than phosphoinositide hydrolysis in the regulation of protein kinase C and perhaps other cell functions.— Exton, J. H. Mechanisms of action of calcium mobilizing agonists: some variations on a young theme.FASEB J.2: 2670‐2676; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.2456243

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Protein kinases represent a diverse family of enzymes that play critical roles in regulation. The simplest and best‐understood biochemically is the catalytic (C) subunit of cAMP‐dependent protein kinase, which can serve as a framework for the entire family. The amino‐terminal portion of the C subunit constitutes a nucleotide binding site based on affinity labeling, labeling of lysines, and a conserved triad of glycines. The region beyond this nucleotide fold also contains essential residues. Modification of Asp 184 with a hydrophobic carbodiimide leads to inactivation, and this residue may function as a general base in catalysis. Despite the diversity of the kinase family, all share a homologous catalytic core, and the residues essential for nucleotide binding or catalysis in the C subunit are invariant in every protein kinase. Affinity labeling and intersubunit cross‐linking have localized a portion of the peptide binding site, and this region is variable in the kinase family. The crystal structure of the C subunit also is being solved. The C subunit is maintained in its inactive state by forming a holoenzyme complex with an inhibitory regulatory (R) subunit. This R subunit has a well‐defined domain structure that includes two tandem cAMP binding domains at the car‐boxy‐terminus, each of which is homologous to the catabolite gene activator protein inEscherichia coli.Affinity labeling with 8N3cAMP has identified residues that are in close proximity to the cAMP binding sites and is consistent with models of the cAMP binding sites based on the coordinates of the CAP crystal structure. An expression vector was constructed for the R1subunit and several mutations have been introduced. These mutations address1) the major site of photoaffinity labeling,2) a conserved arginine in the cAMP binding site, and3) the consequences of deleting the entire second cAMP binding domain.—Taylor, S. S.; Bubis, J.; Toner‐Webb, J.; Saraswat, L. D.; First, E. A.; Buechler, J. A.; Knighton, D. R.; Sowadski, J. cAMP‐dependent protein kinase: prototype for a family of enzymes.FASEB J.2: 2677‐2685; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.3294077

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Many hormones and neurotransmitters attenuate cyclic AMP (cAMP) accumulation in intact cells by virtue of their ability to inhibit adenylate cyclase activity via the GTP‐binding protein denoted as Gi. Nonetheless, a number of physiological findings suggest that attenuation of cAMP production is not sufficient to serve as the only signal for eliciting the diverse physiological effects provoked by these various receptor populations. Additional biochemical and electrophysiological changes are known to occur after occupancy of receptors linked to inhibition of adenylate cyclase, including acceleration of Na+/H+exchange, activation of K+conductances, and inhibition of voltage‐sensitive Ca2+channels. This review summarizes the current understanding of how these receptors are coupled to their multiple potential effector mechanisms and offers some speculation about the possible interplay between the biochemical and electrophysiological sequels of receptor occupancy. It is hoped that future studies will establish which constellation of possible signaling mechanisms actually brings about changes in metabolic, secretory, or contractile events in different target cells.— Limbird, L. E. Receptors linked to inhibition of adenylate cyclase: additional signaling mechanisms.FASEB J.2: 2686‐2695; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.2840317

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Ultraviolet light‐induced pyrimidine dimers in DNA are recognized and repaired by a number of unique cellular surveillance systems. The most direct biochemical mechanism responding to this kind of geno‐toxicity involves direct photoreversal by flavin enzymes that specifically monomerize pyrimidine:pyrimidine dimers monophotonically in the presence of visible light. Incision reactions are catalyzed by a combined pyrimidine dimer DNA‐glycosylase:apyrimidinic en‐donuclease found in some highly UV‐resistant organisms. At a higher level of complexity,Escherichia colihas auvrDNA repair system comprising the UvrA, UvrB, and UvrC proteins responsible for incision. There are several preincision steps governed by this pathway, which includes an ATP‐dependent UvrA dimerization reaction required for UvrAB nucleoprotein formation. This complex formation driven by ATP binding is associated with localized topological unwinding of DNA. This same protein complex can catalyze an ATPase‐dependent 5‘ å 3‘‐directed strand displacement of D‐loop DNA or short single strands annealed to a single‐stranded circular or linear DNA. This putative translocational process is arrested when damaged sites are encountered. The complex is now primed for dual incision catalyzed by UvrC. The remainder of the repair process involves UvrD (helicase II) and DNA polymerase I for a coordinately controlled excision‐resynthesis step accompanied by UvrABC turnover. Furthermore, it is proposed that levels of repair proteins can be regulated by proteolysis. UvrB is converted to truncated UvrB∗ by a stress‐induced protease that also acts at similar sites on theE. coliAda protein. Although UvrB∗ can bind with UvrA to DNA, it cannot participate in helicase or incision reactions. It is also a DNA‐dependent ATPase.—Grossman, L.; Caron, P. R.; Mazur, S. J.; Oh, E. Y. Repair of DNA‐containing pyrimidine dimers.FASEB J.2: 2696‐2701; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.3294078

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

The rise in cytosolic free Ca2+, shape change, superoxide formation, and granule exocytosis induced in human neutrophils by N‐formyl‐Met‐Leu‐Phe (fMLP) and by a newly discovered activating peptide, neutrophil‐activating factor, termed NAF, were compared. NAF was effective in the concentration range of 0.1‐10 nM and was 10‐to 100‐fold more potent than fMLP. In qualitative terms, the single responses to either stimulus were remarkably similar: they showed virtually identical onset and initial kinetics, and were all inhibited by pretreatment of the neutrophils withBordetella pertussistoxin. In addition, the respiratory burst elicited by either stimulus was inhibited by 17‐hydroxywortmannin and staurosporine. Two conclusions are drawn from these results:1)neutrophil activation by NAF (as by fMLP) is dependent on a GTP‐binding protein and on protein kinase C;2) a similar, or even identical, mechanism of signal transduction must be assumed on stimulation of human neutrophils with NAF, fMLP, and other chemotactic agonists. Human monocytes, lymphocytes, and platelets did not show cytosolic free Ca2+changes when exposed to NAF, which suggests that NAF is selective for the neutrophils.— Thelen, M.; Peveri, P.; Kernen, P.;vonTscharner, V; Walz, A.; Baggiolini, M. Mechanisms of neutrophil activation by NAF, a novel monocyte‐derived peptide agonist.FASEB J.2: 2702‐2706; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.2840318

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Benzodiazepines, a class of drugs widely employed as anxiolytics and anticonvulsants, can induce impairments of learning and memory. The purpose of the present investigation was to determine if a benzodiazepine receptor antagonist, flumazenil (Ro 15‐1788), could enhance learning and memory. Pretraining injection of flumazenil (2.5 to 40.0 mg/kg) was found to enhance both learning and memory in a test requiring young mice to discriminate the correct arm of a T‐maze to escape mild electric shock. In a second test, which required mice to passively avoid a dark chamber after shock, flumazenil pretreatment prevented the occurrence of amnesia induced by the cholinergic receptor antagonist scopolamine. It is hypothesized that flumazenil may facilitate learning or memory processes by reversing a negative modulatory influence of endogenous diazepam‐like ligands for benzodiazepine receptors.— Lal, H.; Kumar, B.; Forster, M. J. Enhancement of learning and memory in mice by a benzodiazepine antagonist.FASEB J.2: 2707‐2711; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.3135223

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Human and rabbit plasma contains a lipid transfer protein that transfers cholesteryl esters and triglycerides among the plasma lipoproteins and may also have a role in the movement of lipids into and out of cells. Little is known about the regulation of the activity of the lipid transfer protein, but in the rabbit, hypercholesterolemia is associated with increased plasma lipid transfer activity (LTA). Perfused rabbit livers secrete LTA, and hepatic cholesterol secretion is increased in rabbits with diet‐induced hypercholesterolemia. Thus, experiments were performed with rabbits to determine if LIA is regulated by a concerted hepatic secretion of lipoprotein cholesterol and LTA. Rabbits were fed chow or chow plus coconut oil (14% wt/wt), and plasma lipids, LTA, and the rate of secretion of cholesterol into plasma were determined. Coconut oil feeding increased plasma cholesterol by 68%, LTA by 42%, and hepatic cholesterol secretion by 69%. Mevinolin (75 mg/day), an inhibitor of cholesterol biosynthesis, lowered LTA and plasma cholesterol without affecting the rate of secretion of cholesterol into plasma. These studies provide further evidence that, in the rabbit, plasma cholesterol and LTA are closely related, and the association is not likely to be caused by a concerted hepatic secretion of cholesterol and LTA.—Quig, D. W.; Zilversmit, D. B. Dissociation between cholesterol secretion and plasma lipid transfer activity in rabbits.FASEB J.2: 2712‐2716; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.3396808

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

Monolayer cultures of human mesothelial cells made quiescent by serum deprivation are induced to undergo one round of DNA synthesis by platelet‐derived growth factor (PDGF), epidermal growth factor (EGF), or transforming growth factor type β1 (TGF‐β1). This onetime stimulation is independent of other serum components. The kinetics for induction of DNA synthesis observed for PDGF, EGF, and TGF‐β1 are all similar to one another, with a peak of DNA synthesis occurring 24‐36 h after the addition of the growth factors. Repetitive rounds of DNA synthesis and cell division do not ensue after addition of PDGF, EGF, or TGF‐β1 alone or in combination; however, in media supplemented with chemically denatured serum, each of these factors is capable of sustaining continuous replication of mesothelial cells. Stimulation of growth by PDGF and TGF‐β1 is unusual for an epithelial cell type, and indicates that mesothelial cells have growth regulatory properties similar to connective tissue cells.— Gabrielson, E. W.; Gerwin, B. I.; Harris, C. C.; Roberts, A. B.; Sporn, M. B.; Lechner,j. F. Stimulation of DNA synthesis in cultured primary human mesothelial cells by specific growth factors.FASEB J.2: 2717‐2721; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.3260881

出版商:Wiley    

年代:1988

数据来源: WILEY

摘要:

A corticosteroid with mixed glucocorticoid‐mineralo‐corticoid actions was previously shown to improve neuromuscular function in muscular dystrophic chickens. The significance of that finding was recently underscored by reports that a mixed‐action corticosteroid improved muscle function in Duchenne dystrophy patients, albeit at high doses. In the present study a pure glucocorticoid improved function and retarded muscle histopathology in the chicken, but a pure mineralocorticoid did not. These observations suggest that elucidation of mechanisms by which glucocorticoids beneficially affect dystrophic muscle could lead to development of more effective therapies.— Entrikin, R. K.; Abresch, R. T; Bradford, D. P.; Larson, D. B.; Longley, K.J.; Wilson, B. W. Glucocorticoids in muscular dystrophy: beneficial effects of dexamethasone on avian myopathy.FASEB J.2: 2722‐2725; 1988.

ISSN:0892-6638    

DOI:10.1096/fasebj.2.11.3396809

出版商:Wiley    

年代:1988

数据来源: WILEY