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Biomedical subjects

J Moss

Publications and source records attributed to J Moss.

At least 145 records · Page 8Linked to original sources
PubMed1998

Muscle fibre characteristics and lactate responses to exercise in chronic fatigue syndrome.

OBJECTIVES: To examine the proportions of type 1 and type 2 muscle fibres and the degree of muscle fibre atrophy and hypertrophy in patients with chronic fatigue syndrome in relation to lactate responses to exercise, and to determine to what extent any abnormalities found might be due to inactivity. METHODS: Quadriceps needle muscle biopsies were obtained from 105 patients with chronic fatigue syndrome and the proportions of type 1 and 2 fibres and fibre atrophy and hypertrophy factors were determined from histochemical preparations, using a semiautomated image analysis system. Forty one randomly selected biopsies were also examined by electron microscopy. Lactate responses to exercise were measured in the subanaerobic threshold exercise test (SATET). RESULTS: Inactivity would be expected to result in a shift to type 2 fibre predominance and fibre atrophy, but type 1 predominance (23%) was more common than type 2 predominance (3%), and fibre atrophy was found in only 10.4% of cases. Patients with increased lactate responses to exercise did have significantly fewer type 1 muscle fibres (p<0.043 males, p<0.0003 females), but there was no evidence that this group was less active than the patients with normal lactate responses. No significant ultrastructural abnormalities were found. CONCLUSION: Muscle histometry in patients with chronic fatigue syndrome generally did not show the changes expected as a result of inactivity. However, patients with abnormal lactate responses to exercise had a significantly lower proportion of mitochondria rich type 1 muscle fibres.

Adult↗
PubMed1998

Effects of low-dose morphine on gastric emptying in healthy volunteers.

Appropriate preoperative pain therapy for patients undergoing surgery may be withheld due to the fear that opioids will inhibit gastric emptying and increase the risk of aspiration. Previously, doses of 5 to 10 mg of morphine have been shown to delay gastric emptying time. However, the effect of lower doses of morphine on gastric emptying in humans has not been reported. In this study, the effects of intravenous morphine 0.05 mg/kg-3.5 mg for 70-kg body weight, a dose that can cause analgesia--on gastric emptying were evaluated in a double-blind, randomized, placebo-controlled study in 15 healthy human volunteers using the acetaminophen test. Our data indicated that this low dose of morphine significantly prolonged the gastric emptying time. Thus, even small doses of morphine inhibit gastric emptying. This effect may be important in patients undergoing surgery, in patients receiving other oral medications after surgery in ambulatory settings, and in instances of patient-controlled analgesia.

Acetaminophen↗
PubMed1998

An ultrastructural study of the colocalization of biglycan and decorin with AA amyloid fibrils in human renal glomeruli.

An investigation was undertaken on paraformaldehyde-fixed, Lowicryl resin-embedded renal biopsies from patients with AA amyloidosis to study the association of two small chondroitin sulphate/dermatan sulphate proteoglycans, decorin and biglycan, with amyloid fibrils using an ultrastructural immunogold technique. Biglycan was present in glomerular endothelial cells in both normal kidney and in amyloidosis, but little biglycan or decorin was present in the normal mesangial matrix. By contrast, conspicuous amounts of both biglycan and decorin were seen to be associated with amyloid fibrils in the glomerular matrix in cases of renal AA amyloidosis. The results further emphasise the close association between amyloid and extracellular matrix components which are now considered to be an integral part of the amyloid fibrils.

Amyloidosis↗
PubMed1998

Immunohistochemical analysis of proteins of the Bcl-2 family in pulmonary lymphangioleiomyomatosis: association of Bcl-2 expression with hormone receptor status.

BACKGROUND: Pulmonary lymphangioleiomyomatosis (LAM), a disease of young women, is characterized by proliferation of abnormal smooth muscle cells (LAM cells), which often differ from normal pulmonary smooth muscle cells by frequently having estrogen and progesterone receptors. OBJECTIVE: To evaluate the relationships among several factors related to proliferation and apoptosis in LAM cells, we employed immunohistochemical methods for the localization of Bcl-2 and Mcl-1 (inhibitors of apoptosis), Bax (a promoter of apoptosis), c-Myc (an apoptosis-related oncoprotein), proliferating cell nuclear antigen (an indicator of mitotic activity), and nick end labeling (to identify apoptotic cells) in lung tissues of 9 patients with LAM. RESULTS: In all patients, most LAM cells reacted positively for Bax. The LAM cells were positive for both Bcl-2 and estrogen receptor in 5 patients, positive for only Bcl-2 in 1 patient, positive for only estrogen receptor in another patient, and negative for both in 2 patients. More than 50% of the Bcl-2-positive LAM cells were also positive for estrogen receptor. The reaction for c-Myc was positive in all patients. The immunoreactivity for Bcl-2 and Mcl-1, which inhibit apoptosis, was more intense in LAM cells than in normal vascular and bronchial smooth muscle cells. In 6 patients, more than 50% of the LAM cells were positive for proliferating cell nuclear antigen. Apoptosis was infrequent in LAM cells. CONCLUSIONS: Our results suggest that the expression of Bcl-2 in LAM cells may be related to hormonal regulation, and that by decreasing apoptosis, Bcl-2 and related proteins contribute to the imbalance between proliferation and death of LAM cells.

Adult↗
PubMed1998

Economic analysis and general practice.

At this time innovation in general practice service delivery is being extensively explored and critically examined as a means of improving efficiency. It is important that general practitioners are actively involved in the debate and utilise techniques that allow detailed, logical and robust judgments to be formulated. Economic analysis is one important tool that can contribute to these judgments. The aim of this article is to provide a brief overview of the concepts and methods used.

Costs and Cost Analysis↗
PubMed1997

Characterization of an ADP-ribosylation factor-like 1 protein in Saccharomyces cerevisiae.

ADP-ribosylation factors (ARFs) are highly conserved approximately 20-kDa guanine nucleotide-binding proteins that enhance the ADP-ribosyltransferase activity of cholera toxin and are believed to participate in vesicular transport in both exocytic and endocytic pathways. Several ARF-like proteins (ARLs) have been cloned from Drosophila, rat, and human; however, the biological functions of ARLs are unknown. We have identified a yeast gene (ARL1) encoding a protein that is structurally related (>60% identical) to human, rat, and Drosophila ARL1. Biochemical analyses of purified recombinant yeast ARL1 (yARL1) protein revealed properties similar to those ARF and ARL1 proteins, including the ability to bind and hydrolyze GTP. Like other ARLs, recombinant yARL1 protein did not stimulate cholera toxin-catalyzed auto-ADP-ribosylation. yARL1 was not recognized by antibodies against mammalian ARLs or yeast ARFs. Anti-yARL1 antibodies did not cross-react with yeast ARFs, but did react with human ARLs. On subcellular fractionation, yARL1, similar to yARF1, was localized to the soluble fraction. The amino terminus of yARL1, like that of ARF, was myristoylated. Unlike Drosophila Arl1, yeast ARL1 was not essential for cell viability. Like rat ARL1, yARL1 might be associated in part with the Golgi complex. However, yARL1 was not required for endoplasmic reticulum-to-Golgi protein transport, and it may offer an opportunity to define an ARL function in another kind of vesicular trafficking, such as the regulated secretory pathway.

ADP-Ribosylation Factors↗
PubMed1997

Cloning and expression of a cDNA encoding a bovine brain brefeldin A-sensitive guanine nucleotide-exchange protein for ADP-ribosylation factor.

A 200-kDa guanine nucleotide-exchange protein (p200 or GEP) for ADP-ribosylation factors 1 and 3 (ARF1 and ARF3) that was inhibited by brefeldin A (BFA) was purified earlier from cytosol of bovine brain cortex. Amino acid sequences of four tryptic peptides were 47% identical to that of Sec7 from Saccharomyces cerevisiae, which is involved in vesicular trafficking in the Golgi. By using a PCR-based procedure with two degenerate primers representing sequences of these peptides, a product similar in size to Sec7 that contained the peptide sequences was generated. Two oligonucleotides based on this product were used to screen a bovine brain library, which yielded one clone that was a partial cDNA for p200. The remainder of the cDNA was obtained by 5' and 3' rapid amplification of cDNA ends (RACE). The ORF of the cDNA encodes a protein of 1,849 amino acids (approximately 208 kDa) that is 33% identical to yeast Sec7 and 50% identical in the Sec7 domain region. On Northern blot analysis of bovine tissues, a approximately 7.4-kb mRNA was identified that hybridized with a p200 probe; it was abundant in kidney, somewhat less abundant in lung, spleen, and brain, and still less abundant in heart. A six-His-tagged fusion protein synthesized in baculovirus-infected Sf9 cells demonstrated BFA-inhibited GEP activity, confirming that BFA sensitivity is an intrinsic property of this ARF GEP and not conferred by another protein component of the complex from which p200 was originally purified.

ADP-Ribosylation Factor 1↗
PubMed1997

Pertussis toxin-sensitive G proteins as mediators of the signal transduction pathways activated by cytomegalovirus infection of smooth muscle cells.

We demonstrated recently that the arachidonic acid (AA) cascade is involved in cytomegalovirus (CMV)-induced generation of reactive oxygen species (ROS) and the activation of nuclear factor (NF)-kappaB in human smooth muscle cells (SMCs). Since AA release from neutrophils is mediated by pertussis toxin (PTx)-sensitive guanine nucleotide-binding (G) proteins, we hypothesized by analogy that CMV stimulates ROS generation in SMCs and ultimately activates NF-kappaB via a PTx-sensitive G protein-coupled pathway. Our first test of this hypothesis demonstrated that PTx blocked AA release induced by CMV infection of SMCs, as well as blocked the terminal products of this reaction, ROS generation and NF-kappaB activation. More proximal components of the pathway were then examined. CMV infection increased phosphorylation and activity of cytosolic phospholipase A2 (cPLA2), an enzyme causing AA release; these effects were inhibited by PTx. CMV infection activated mitogen-activated protein (MAP) kinase, a key enzyme for cPLA2 phosphorylation, an effect also inhibited by PTx. Finally, inhibition of MAP kinase kinase (MAPKK), which phosphorylates and thereby activates MAP kinase, inhibited CMV-induced ROS generation. These data demonstrate that a PTx-sensitive G protein-dependent signaling pathway mediates cellular effects of CMV infection of SMCs. The downstream events include phosphorylation and activation of MAP kinase by MAPKK and subsequent phosphorylation and activation of cPLA2 (with its translocation to cell membranes), followed by stimulation of the AA cascade, which generates intracellular ROS and thereby activates NF-kappaB.

Aorta↗
PubMed1997

Characterization of a GDP dissociation inhibitory region of ADP-ribosylation factor domain protein ARD1.

ADP-ribosylation factors (ARFs) are approximately 20-kDa guanine nucleotide-binding proteins initially identified by their ability to stimulate cholera toxin ADP-ribosyltransferase activity and later recognized as critical components in intracellular vesicular transport and phospholipase D activation. ARF domain protein 1 (ARD1) is a member of the ARF family that differs from other ARFs by the presence of a 46-kDa amino-terminal extension. We previously reported that this extension acts as a GTPase-activating protein for the ARF domain of ARD1 (Vitale, N., Moss, J., and Vaughan, M. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 1941-1944). Both GTP binding and GTP hydrolysis are necessary for physiological function of guanine nucleotide-binding proteins, and the rates of GDP/GTP exchange and GTPase activity are critical in the activation/deactivation cycle. Dissociation of GDP from the ARF domain of ARD1 was faster than from ARD1 itself (both proteins synthesized in Escherichia coli). Using deletion mutations, it was demonstrated that the 15 amino acids directly preceding the ARF domain were responsible for decreasing the rate of GDP dissociation but not guanosine 5-[gamma-thio]triphosphate dissociation. By site-specific mutagenesis it was shown that hydrophobic amino acids in this region were particularly important in stabilizing the GDP-bound form of ARD1. It is suggested that, like the amino-terminal segment of ARF, the equivalent region in ARD1, located between the GTPase-activating protein and ARF domains, may act as a GDP dissociation inhibitor.

ADP-Ribosylation Factors↗
PubMed1997

Expression in BALB/c and C57BL/6 mice of Rt6-1 and Rt6-2 ADP-ribosyltransferases that differ in enzymatic activity: C57BL/6 Rt6-1 is a natural transferase knockout.

Several proteins with NAD+:arginine ADP-ribosyltransferase (ART) activity are expressed in T cells and affect their function. Rat T cells that express the ART designated RT6 are determinants of the expression of autoimmune diabetes. In the mouse, a 35-kDa ecto-ART modulates the proliferation and functional activity of CTL. Here we report on mouse ARTs designated Rt6-1 and Rt6-2 in BALB/c and C57BL/6 mice. mRNAs for Rt6-1 and Rt6-2 were found in spleen, thymus, and intestinal tissue of both strains, but Rt6-1 mRNA in C57BL/6 mice was detected only at low levels. Rt6-1 and Rt6-2 cDNAs from both strains were cloned and sequenced. Predicted amino acid sequences of Rt6-2 were identical in both strains, but there was an in-frame stop codon in the sequence of Rt6-1 in C57BL/6 mice not present in BALB/c mice. Recombinant C57BL/6 Rt6-2 and BALB/c Rt6-1 proteins expressed in COS1 cells exhibited ART activity and were documented to be glycosylphosphatidylinositol-linked membrane proteins. COS-1 cells transfected with a C57BL/6 Rt6-1 cDNA construct expressed a truncated protein consistent in size with that predicted by the presence of the stop codon. This approximately 21-kDa protein appeared not to be glycosylphosphatidylinositol linked to the cell surface and lacked ART activity. C57BL/6 Rt6-1 therefore appears to be a naturally occurring ART knockout. The expression of Rt6-1 and Rt6-2 mRNAs in lymphoid tissues suggests that these ARTs may regulate immune system functions. Expression of Rt6-2 or another redundant ART may compensate for the lack of enzymatically active Rt6-1 in C57BL/6 mice.

ADP Ribose Transferases↗
PubMed1997

An 18-kDa domain of a glycosylphosphatidylinositol-linked NAD:arginine ADP-ribosyltransferase possesses NAD glycohydrolase activity.

Transfection of NMU (rat mammary adenocarcinoma) cells with NAD:arginine ADP-ribosyltransferase cDNAs from Yac-1 murine lymphoma cells or rabbit muscle increased NAD glycohydrolase and ADP-ribosyltransferase activities. The ADP-ribosyltransferase activity was released from transformed NMU cells by phosphatidylinositol-specific phospholipase C (PI-PLC) and hence glycosylphosphatidylinositol (GPI)-anchored, whereas the NAD glycohydrolase (NADase) activity remained cell-associated. By gel permeation chromatography, the size of the PI-PLC-released transferase was approximately 40 kDa and that of the detergent-solubilized NADase was approximately 100 kDa. Using polyclonal antibodies against rabbit muscle transferase on Western blots, approximately 18- and approximately 30-kDa band were visualized among proteins from the NADase fractions and 38-40-kDa bands with protein from the transferase fractions. Incubation of blots with [32P]NAD led to the incorporation of radioactivity into the immunoreactive transferase bands of 38 kDa and the immunoreactive NADase band of approximately 18 kDa. These data suggest that proteolysis of ADP-ribosyltransferase synthesized in transformed NMU cells might result in the formation of aggregates of an 18-kDa NAD glycohydrolase. A fusion protein with glutathione S-transferase linked to the amino terminus of Yac-1 transferase, from which the amino-terminal 121 amino acids had been deleted (GST-Yac-1-delta121), exhibited NADase, but not transferase, activity. The size of the recombinant fusion protein was similar to that of the proteolytic fragment seen in NMU cells transformed with transferase cDNA. These results are compatible with the conclusion that the NAD glycohydrolase activity was generated in NMU cells by proteolysis of ADP-ribosyltransferase, with release of a carboxyl-terminal fragment that possesses glycohydrolase but not transferase activity, i.e. the carboxyl-terminal portion of the transferase can exist as a catalytically active NADase.

ADP Ribose Transferases↗
PubMed1997

Cytohesin-1, a cytosolic guanine nucleotide-exchange protein for ADP-ribosylation factor.

Cytohesin-1, a protein abundant in cells of the immune system, has been proposed to be a human homolog of the Saccharomyces cerevisiae Sec7 gene product, which is crucial in protein transport. More recently, the same protein has been reported to be a regulatory factor for the alphaLbeta2 integrin in lymphocytes. Overexpression of human or yeast ADP-ribosylation factor (ARF) genes rescues yeast with Sec7 defects, restoring secretory pathway function. ARFs, 20-kDa guanine nucleotide-binding proteins initially identified by their ability to stimulate cholera toxin ADP-ribosyltransferase activity and now recognized as critical components in intracellular vesicular transport, exist in an inactive cytosolic form with GDP bound (ARF-GDP). Interaction with a guanine nucleotide-exchange protein (GEP) accelerates exchange of GDP for GTP, producing the active ARF-GTP. Both soluble and particulate GEPs have been described. To define better the interaction between ARF and Sec7-related proteins, effects of cytohesin-1, synthesized in Escherichia coli, on ARF activity were evaluated. Cytohesin-1 enhanced binding of 35S-labeled guanosine 5'-[gamma-thio]triphosphate [35S]GTP[gammaS] or [3H]GDP to ARF purified from bovine brain (i.e., it appeared to function as an ARF-GEP). Addition of cytohesin-1 to ARF3 with [35S]GTP[gammaS] bound, accelerated [35S]GTP[gammaS] release to a similar degree in the presence of unlabeled GDP or GTP[gammaS] and to a lesser degree with GDP[betaS]; release was negligible without added nucleotide. Cytohesin-1 also increased ARF1 binding to a Golgi fraction, but its effect was not inhibited by brefeldin A (BFA), a drug that reversibly inhibits Golgi function. In this regard, it differs from a recently reported BFA-sensitive ARF-GEP that contains a Sec7 domain.

ADP-Ribosylation Factor 1↗
PubMed1997

Interaction of the GTP-binding and GTPase-activating domains of ARD1 involves the effector region of the ADP-ribosylation factor domain.

ADP-ribosylation factors (ARFs) are a family of approximately 20-kDa guanine nucleotide-binding proteins and members of the Ras superfamily, originally identified and purified by their ability to enhance the ADP-ribosyltransferase activity of cholera toxin and more recently recognized as critical participants in vesicular trafficking pathways and phospholipase D activation. ARD1 is a 64-kDa protein with an 18-kDa carboxyl-terminal ARF domain (p3) and a 46-kDa amino-terminal extension (p5) that is widely expressed in mammalian tissues. Using recombinant proteins, we showed that p5, the amino-terminal domain of ARD1, stimulates the GTPase activity of p3, the ARF domain, and appears to be the GTPase-activating protein (GAP) component of this bifunctional protein, whereas in other members of the Ras superfamily a separate GAP molecule interacts with the effector region of the GTP-binding protein. p5 stimulated the GTPase activity of p3 but not of ARF1, which differs from p3 in several amino acids in the effector domain. After substitution of 7 amino acids from p3 in the appropriate position in ARF1, the chimeric protein ARF1(39-45p3) bound to p5, which increased its GTPase activity. Specifically, after Gly40 and Thr45 in the putative effector domain of ARF1 were replaced with the equivalent Asp and Pro, respectively, from p3, functional interaction of the chimeric ARF1 with p5 was increased. Thus, Asp25 and Pro30 of the ARF domain (p3) of ARD1 are involved in its functional and physical interaction with the GTPase-activating (p5) domain of ARD1. After deletion of the amino-terminal 15 amino acids from ARF1(39-45p3), its interaction with p5 was essentially equivalent to that of p3, suggesting that the amino terminus of ARF1(39-45p3) may interfere with binding to p5. These results are consistent with the conclusion that the GAP domain of ARD1 interacts with the effector region of the ARF domain and thereby stimulates GTP hydrolysis.

ADP-Ribosylation Factor 1↗
PubMed1997

Characterization of mouse Rt6.1 NAD:arginine ADP-ribosyltransferase.

Rat RT6 proteins, and perhaps mouse Rt6, identify a set of immunoregulatory T lymphocytes. Rat RT6.1 (RT6.1) and rat RT6.2 (RT6. 2) are NAD glycohydrolases, which catalyze auto-ADP-ribosylation, but not ADP-ribosylation of exogenous proteins. Mouse Rt6.1 (mRt6.1) also catalyzes auto-ADP-ribosylation. The activity of mouse cytotoxic T lymphocytes is reportedly inhibited by ADP-ribosylation of surface proteins, raising the possibility that mRt6 may participate in this process. The reactions catalyzed by mRt6, would, however, need to be more diverse than those of the rat homologues and include the ADP-ribosylation of acceptors other than itself. To test this hypothesis, mRt6.1 and rat RT6.2 were synthesized in Sf9 insect cells and rat mammary adenocarcinoma (NMU) cells. mRt6.1, but not rat RT6.2, catalyzed the ADP-ribosylation of guanidino-containing compounds (e.g. agmatine). Unlike RT6.2, mRt6.1 was a weak NAD glycohydrolase. In the presence of agmatine, however, the ratio of [adenine-14C]ADP-ribosylagmatine formation from [adenine-14C]NAD to [carbonyl-14C]nicotinamide formation from [carbonyl-14C]NAD was approximately 1.0, demonstrating that mRt6.1 is primarily a transferase. ADP-ribosylarginine hydrolase, which preferentially hydrolyzes the alpha-anomer of ADP-ribosylarginine, released [U-14C]arginine from ADP-ribosyl[U-14C]arginine synthesized by mRT6.1, consistent with the conclusion that mRt6.1 catalyzes a stereospecific Sn2-like reaction. Thus, mRt6.1 is an NAD:arginine ADP-ribosyltransferase capable of catalyzing a multiple turnover, stereospecific Sn2-like reaction.

ADP Ribose Transferases↗
PubMed1997

Administration of H1 and H2 antagonists for chemoprophylaxis: a double-blind, placebo-controlled study in healthy volunteers.

A double-blind, placebo-controlled trial was performed to establish the duration of action of antihistamines and their ability to attenuate the adverse affects associated with histamine release. Thirty volunteers were assigned randomly to receive either placebo or a combination of the H1 blocker dimetindene maleate (0.1 mg/kg) and the H2 blocker cimetidine (5 mg/kg). A bolus dose of histamine (450 ng/kg) was given 15 minutes after antihistamine or placebo treatment and repeated after 2, 4, and 6 hours. Cardiovascular variables, plasma histamine levels, cutaneous manifestations, and objective and subjective signs and symptoms associated with histamine release were determined before and after each histamine injection. Although many of the signs of histamine release, including erythema and metallic taste, could be attenuated effectively for 6 hours with antihistamine treatment, the protection against histamine-induced flush and headache diminished after 2 hours. Statistically significant protection against histamine-mediated tachycardia persisted for only 2 hours. Antihistamine treatment significantly reduced the increase in plasma histamine levels after the first histamine injection but did not alter the levels after subsequent histamine injections. The currently recommended administration regimen for prophylaxis with antihistamines is insufficient to prevent histamine-mediated side effects, and additional doses may be required after 4 hours to achieve appropriate chemoprophylaxis.

Adult↗
PubMed1997

Molecular cloning and characterization of lymphocyte and muscle ADP-ribosyltransferases.

Mono-ADP-ribosylation, catalyzed by ADP-ribosyltransferases, is a posttranslational modification of proteins in which the ADP-ribose moiety of NAD is transferred to an acceptor protein(arginine). Several of the bacterial toxin ADP-ribosyltransferases have been well characterized in their ability to alter cellular metabolism. It has been postulated that these bacterial toxins mimic the actions of transferases from mammalian cells. We have cloned and characterized ADP-ribosyltransferases from rabbit and human skeletal muscle, and mouse lymphocytes. The muscle transferases are glycosylphosphatidylinositol (GPI)-anchored proteins that are conserved among species. Two distinct transferases, termed Yac-1 and Yac-2 were cloned from mouse lymphoma (Yac-1) cells. The Yac-1 transferase, like the muscle enzymes, is a GPI-linked exoenzyme. The Yac-2 transferase, on the other hand, is membrane-associated but appears not to be GPI-linked. In contrast to Yac-1, the Yac-2 enzyme had significant NAD glycohydrolase activity and may preferentially hydrolyze NAD. The bacterial toxin ADP-ribosyltransferases contain three noncontiguous regions of sequence similarity, which are involved in formation of the catalytic site. Alignment of the deduced amino acid sequences of the mammalian transferases and the rodent RT6 enzymes, along with results from site-directed mutagenesis of the muscle enzyme, are consistent with the notion of a common mechanism of NAD binding and catalysis among ADP-ribosyltransferases.

ADP Ribose Transferases↗
PubMed1997

ADP-ribosylarginine hydrolases and ADP-ribosyltransferases. Partners in ADP-ribosylation cycles.

Mono-ADP-ribosylation is a reversible modification of arginine residues in proteins, with NAD:arginine ADP-ribosyltransferases and ADP-ribosylarginine hydrolases constituting opposing arms of a putative ADP-ribosylation cycle. The enzymatic components of an ADP-ribosylation cycle have been identified in both prokaryotic and eukaryotic systems. The regulatory significance of the cycle has been best documented in prokaryotes. As shown by Ludden and coworkers, ADP-ribosylation controls the activity of dinitrogenase reductase in the phototropic bacterium Rhodospirillum rubrum. ADP-ribosylation of other amino acids, such as cysteine, has also been demonstrated, lending credence to the hypothesis that this modification is heterogeneous. In eukaryotes, the functional relationship between ADP-ribosyltransferases and ADP-ribosylarginine hydrolases is less well documented. The transferase-catalyzed reaction results in sterospecific formation of alpha-ADP-ribosylarginine from beta-NAD; ADP-ribosylarginine hydrolases specifically cleave the alpha-anomer, leading to release of ADP-ribose and regeneration of the free guanidino group of arginine. The two reactions can thus be coupled in vitro. Coupling in vivo is dependent on cellular localization. The deduced amino acid sequences of ADP-ribosyltransferases from avian and mammalian tissues have common consensus sequences involved in catalytic activity but, in some instances, enzyme-specific cellular localization signals. The presence of amino- and carboxy-terminal signal sequences is consistent with the glycosylphosphatidylinositol(GPI)-anchoring to the cell surface. The muscle and lymphocyte transferases ADP-ribosylate integrins. Some transferases lack the carboxy- terminal signal sequence needed for GPI-anchoring. Most ADP-ribosylarginine hydrolase activity is cytosolic, although perhaps some is located at the cell surface. Deduced amino acid sequences of hydrolases from a number of mammalian species are consistent with their cytoplasmic localization. Katada and coworkers have determined, however, that auto-ADP-ribosylated RT6, a GPI-linked protein, is metabolized by a hydrolase-like activity, consistent with the existence of an ADP-ribosylation cycle. ADP-ribosyl RT6 may be internalized, thereby coming in contact with the cytosolic hydrolase; alternatively, a novel form of the hydrolase may be located at the surface. The mechanism of coupling of ADP-ribosyltransferases and hydrolases in eukaryotic ADP-ribosylation cycles has yet to be clarified.

ADP Ribose Transferases↗