Fiberoptic bronchoscopic Nd-YAG laser therapy in obstructive airway diseases

BACKGROUND

This study reports the results of Neodymium-Yttrium-Aluminum Garnet (Nd-YAG) laser resection on benign and malignant obstructing airway diseases which has been done in our hospital for four years. The effect of this treatment on patients' arterial blood gases, during and after the process is also analyzed. The benefit of adjuvant therapy with radiotherapy and/or chemotherapy after laser vaporization is discussed.

METHODS

Fiberoptic bronchoscopic Nd-YAG laser therapy was performed in 32 cases of lung cancer (primary 27, secondary 5) and 11 cases of benign tracheobronchial diseases with total or near total airway obstruction. The therapy was performed through the oral route under local anesthesia. The result of therapy was classified as "excellent", "fair" or "poor" depending upon the degree of recanalization and clinical improvement. A cannula was inserted into the radial artery in lung cancer patients before the procedure. Samples of blood to determine arterial blood gas levels were drawn before, during and after treatment. After bronchoscopic laser therapy, radiotherapy and/or chemotherapy were given to the patients of lung cancer.

RESULTS

The effective rate (excellent and fair) was 75% in lung cancer and 81.8% in benign airway obstruction. In the lung cancer group, significant decline of PaO2 was noted during and after Nd-YAG laser therapy. Decrease of PaO2 was not recovered even 5 hours after laser vaporization. After bronchoscopic Nd-YAG laser therapy, 21 of 32 lung cancer patients received radiotherapy (at least 3000 rads) and/or chemotherapy (at least 3 times). The median survival time was 5.5 months. The other 11 patients received laser therapy only, with median survival time was 2.9 months (p < 0.05).

CONCLUSIONS

Endobronchial Nd-YAG laser therapy of obstructing lesions has been proved to be effective and relatively safe in well-trained hands. Oxygen supplementation was suggested in patients with hypoxemia before laser therapy. After endobronchial Nd-YAG laser therapy, better survival and life quality result if radiotherapy and/or chemotherapy are added for the lung cancer group.

Multiple mitochondrial DNA deletions associated with age in skeletal muscle of rhesus monkeys

We have examined skeletal muscle for the presence of age-associated mitochondrial DNA (mtDNA) deletions from 16 rhesus monkeys (age range 6-27 years). All animals over 13 years of age contained potential mtDNA deletions, whereas the presence of deletions was greatly reduced or absent in younger animals. The specific deletion patterns varied from individual to individual. Numerous mtDNA deletions accumulate with age in skeletal muscle from a nonhuman primate, indicating that the rhesus monkey may provide an excellent animal model to study mtDNA deletions. Further, the existence of multiple mtDNA deletions supports the possibility that they may contribute to geriatric muscular deficits, which are nearly universal in occurrence yet poorly understood.

Microbial reduction of sulfur dioxide with pretreated sewage sludge and elemental hydrogen as electron donors

It has been demonstrated tht heat- and alkali-pretreated-sewage sludge may serve as an electron donor and carbon source for SO2 reduction by Desulfovibrio desulfuricans. A continuous D. desulfuricans culture was operated for 6 mo with complete reduction of SO2 to H2S. The culture required only minor amounts of mineral nutrients in addition to pretreated sewage sludge. It has also been shown that the sulfate-reducing bacterium Desulfotomaculum orientis can be grown on H2 as an energy source, CO2 as a carbon source, and SO2 as a terminal electron acceptor. Complete reduction of SO2 to H2S was observed.

Reduction of nitric oxide by denitrifying bacteria

Two heterotrophic denitrifying bacteria, Paracoccus denitrificans and Pseudomonas denitrificans, have been shown to utilize nitric oxide (NO) as a terminal electron acceptor and succinate, yeast extract, and heat/alkali pretreated municipal sewage sludge as carbon and energy sources. Complete removal of NO (0.50%) from a feed gas sparged into the cultures was observed. It is suggested that reduction of NO may be a common feature of denitrifying bacteria and that a microbial process to dispose of NO(x) may be economically viable.

Case of difficult intubation overcome by the laryngeal mask airway

A case of difficult intubation is described in which the problem was overcome by use of the laryngeal mask airway (LMA). The patient had difficulty in mouth opening due to severe burn scar contracture around the mouth and limited access prevented tracheal intubation. The use of LMA is shown to have obviated the need for tracheal intubation in the case of a patient whose injuries would have made this technique difficult.

Molecular characterization of a conserved, guanine nucleotide-dependent ADP-ribosylation factor in Drosophila melanogaster

ADP-Ribosylation factors (ARFs) are ubiquitous approximately 20-kDa guanine nucleotide-binding proteins that stimulate cholera toxin-catalyzed ADP-ribosylation in vitro. Because the functional role(s) of ARF in mammalian systems is (are) elusive, we looked for ARF in Drosophila melanogaster, and report the partial purification and molecular cloning of an ARF from Drosophila. We cloned the Drosophila ARF 1 gene without library screening by a combination of 5 polymerase chain reactions (PCRs), yielding a 546-base open reading frame encoding 182 amino acids, which are > 93% identical to those of mammalian class I ARFs. This ARF gene maps to 79F3-6 in the proximal region of the left arm of Drosophila chromosome 3. The Drosophila ARF1 gene structure, including placement of introns, is highly conserved relative to mammalian class 1 ARF genes. A single ARF mRNA species of 1.8 kb was abundant in all Drosophila body segments. Recombinant Drosophila ARF 1 synthesized in Escherichia coli had biochemical and immunochemical activities similar to those of mammalian ARF. The similarities of sequence and biochemical properties between Drosophila and mammalian ARFs contrast with their differences from Drosophila arl (ARF-like protein), which does not stimulate cholera toxin-catalyzed ADP-ribosylation, and is only approximately 52-56% identical in amino acid sequence to mammalian ARFs.

Calcium antagonistic and antiarrhythmic actions of CPU-23, a substituted tetrahydroisoquinoline

1. The effects of CPU-23 (1-(1-[(6-methoxyl)-naphth-2-yl])-propyl-2-(1-piperidine)-acetyl-6 ,7- dimethyoxy-1,2,3,4-tetra-hydroisoquinoline) were studied on mechanical and electrical activities, and intracellular free calcium ([Ca2+]i) of isolated cardiac tissues in order to investigate its spectrum and mechanisms of action in the heart. Its antiarrhythmic and haemodynamic effects in pentobarbitone-anaesthetized rats subjected to coronary artery ligation were also evaluated. 2. CPU-23 at 10(-6)-10(-4) M markedly inhibited slow action potential characteristics in guinea-pig papillary muscles and pace-maker action potential of rabbit sinoatrial node. It affected fast action potential only at 10(-4) M. None of the effects of CPU-23 was reversed by washout for up to 2 h. 3. Like nifedipine and diltiazem, CPU-23 decreased the heart rate of the isolated perfused heart of the rat. However, in contrast to these two classical calcium antagonists which dose-dependently inhibited the force of contraction, CPU-23 inhibited and stimulated the force of contraction at 10(-7)-3 x 10(-6) M and 10(-5) M, respectively. 4. CPU-23 at 10(-6)-10(-5) M inhibited the KCl-induced [Ca2+]i increase in the Ca2+ medium, but did not affect the caffeine-induced [Ca2+]i increase in the Ca(2+)-free medium in isolated ventricular myocytes. 5. CPU-23 at 1-5 mg kg-1 reduced dose-dependently ventricular arrhythmias including ventricular ectopic beats, VT and VF as well as mortality during coronary artery ligation. At 2.5-5 mg kg-1 it even abolished VF, which was accompanied by 100% survival. 6. It is suggested that CPU-23 has calcium antagonistic properties in cardiac tissues. It selectively blocks the transmembrane influx of extracellular Ca2+ through Ca2+ channels, thus reducing the heart rate and developed tension, altering the slow action potential characteristics and producing antiarrhythmic effect against ischaemic arrhythmias.

Clinical norms for amplitude of accommodation in Chinese

Amplitude of accommodation was measured in 121 Hong Kong Chinese subjects between the ages of 11 and 65 years, using the 'push-up' method and the results compared with those previously obtained for Caucasian subjects. The results confirm and quantify clinical experience that Chinese people have lower amplitudes of accommodation than Caucasians. If presbyopia is considered to commence when the amplitude of accommodation declines to less than 5 D, then presbyopia in the Chinese race occurs between the ages of 36 and 40 years. By early in the second decade of life the amplitude of accommodation in the Chinese is already lower than that of Caucasians. This suggests that reduced amplitude of accommodation may be due, at least in part, to factors other than longterm environmental effects.

Hip fracture incidence in Malaysia 1981-1989

The age-corrected incidence of hip fracture in the city of Kuala Lumpur and the surrounding districts has increased from 1981 to 0.7 per 1,000 population in 1989. Women dominated by a factor of 1.3. The mean age was 73 (50-103) years. The increased rate observed was attributed solely to trochanteric fractures among those 70 years and above. There were differences in the various parameters among the different races. The fracture incidence and woman/man ratio were substantially lower than has been reported from developed countries.

The management of complicated hepatolithiasis with intrahepatic biliary stricture by the combination of T-tube tract dilation and endoscopic electrohydraulic lithotripsy

Hepatolithiasis with intrahepatic biliary strictures, more common in Southeast Asia than elsewhere, remains a difficult problem to manage. Retention of stones behind strictures after surgery is a frequent and troublesome complication. Post-operative duct dilation with percutaneous transhepatic cholangioscopy tube stenting through a matured T-tube tract was performed in 15 patients. Choledochoscopic electrohydraulic lithotripsy was applied in six patients when impacted or large stones were encountered. Complete clearance of stones was achieved in 12 patients (80%). Two patients had fevers develop after ductal dilation and recovered after conservative treatment. These 12 successfully treated patients remain well, with a mean follow-up of 18 months. Post-operative T-tube tract dilation, selectively combined with endoscopic electrohydraulic lithotripsy, is an effective and safe method for complicated hepatolithiasis with biliary strictures.

Conformational study of two substance P hexapeptides by two-dimensional NMR

The conformation of two substance P (SP) related hexapeptides. Glp-Phe-Phe-(L-Pro)-Leu-Met.NH2 (I) and Glp-Phe-Phe-(D-Pro)-Leu-Met.NH2 (II), in two solvents, chloroform-d and trifluoroethanol(TFE)-d3/H2O, was studied by two-dimensional NMR methods, including COSY, TOCSY, ROESY and HMQC. The study shows that these two peptides exist predominantly in the extended form in TFE/H2O, but in general exhibit a reverse-turn structure in chloroform. I is clearly less ordered than II in both solvents. Furthermore, extensive Phe3-Pro4 cis<==>trans isomerization was found in I but not in II. The differences in the conformational behavior of these two peptides, which are selective agonists for neurokinin NK1 and NK2 receptors, respectively, are discussed.

Eosinophilic gastroenteritis: 10 years experience

Eight patients (five men, three women), mean age 36.9 +/- 13.5 (17-60) yr, were diagnosed to have eosinophilic gastroenteritis. The condition was proved in five patients by biopsies through endoscope, and in three, by operation. All had hypereosinophilia (absolute eosinophil count of 1,337-21,787/cm3). According to Klein classification, two had mucosal disease, three had muscle layer disease, and three, subserosal disease. The most common symptoms were abdominal pain (100%), diarrhea (62.5%), vomiting (62.5%), and nausea (50%). Four patients (50%) had symptoms for more than 1 yr before diagnosis. Barium studies revealed mucosal edema and/or thickening of the small intestinal wall in three cases (including one case with ulceration), partial gastric outlet obstruction in one case, and narrowing of lumen of the terminal ileum in one case. Hypotonic duodenogram revealed double contour in one case. Ultrasound examination revealed thickening of the intestinal wall in two cases; computer tomography revealed thickening of the intestinal wall in one case. All patients were treated with steroid (40 mg/day for initial dose and relapse; 5-10 mg/day for maintenance). The symptoms subsided and the eosinophil counts returned to normal within 2 wk in seven patients and 1 month in one. Of six patients being followed up for 2-10 yr, one had remission, four needed small maintenance dose of steroid, and one suffered from relapse with intestinal perforation.

Lithospermic acid B as an antioxidant-based protector of cultured ventricular myocytes and aortic endothelial cells of rabbits

Lithospermic acid B, an active principle found in a Chinese herbal medicine for treating various heart ailments, was recently isolated, purified and demonstrated by us to salvage the postischemic rabbit heart from reperfusion injury. In this work, we further report that lithospermate B is able to protect each of two types of rabbit cardiocytes, namely ventricular myocytes and aortic endothelial cells against necrosis inflicted by oxyradicals generated pharmacologically with xanthine oxidase and hypoxanthine. Biochemically, the lithospermate B also inhibits the reduction of cytochrome c by superoxide radical anion. Thus, our in vitro data here are in concord with our earlier in vivo finding that lithospermic acid B is most likely an effective antioxidant-based myocardial protector.

Demonstration of the myocardial salvage effect of lithospermic acid B isolated from the aqueous extract of Salvia miltiorrhiza

Lithospermic acid B has been isolated to > 95% purity by high performance liquid chromatography from the aqueous extract of the roots of Salvia miltiorrhiza. When infused at 5.5 mumoles/kg into the post-ischemic rabbit heart, it reduced by 62 +/- 10% (n = 8) the myocardial damage found in the saline control in a rabbit ischemia-reperfusion model.

Sequential invasions of pancreatic pseudocysts in pancreatic tail, hepatic left lobe, caudate lobe, and spleen

A 66-year-old male patient without a history of risk factors for pancreatitis suffered from pancreatitis and developed pseudocyst. During the course of treatment and follow-up, the pseudocyst was found to have migrated through the pancreatic tail, left hepatic lobe, caudate lobe, and spleen on abdominal sonography and computed tomography scan. Finally, emergent laparotomy was done for splenic abscess and removal of infected pseudocyst in the spleen and lesser sac of the abdomen. The patient made a full recovery after operation.

Serum-ascites albumin concentration gradient and ascites fibronectin in the diagnosis of malignant ascites

BACKGROUND

The differential diagnosis between malignant and nonmalignant ascites by using laboratory parameters has not been completely achieved so far.

METHODS

The authors studied serum-ascites albumin concentration gradients ([albumin]s - [albumin]a), ascites fibronectin and various parameters in 149 consecutive patients with ascites (including Group 1: 22 patients with intraabdominal malignant lesions; Group 2: 81 patients with chronic liver disease; and Group 3: 46 patients with hepatocellular carcinoma [HCC]).

RESULTS

The concentrations of fibronectin, albumin, protein, lactate dehydrogenase, and carcinoembryonic antigen in ascites were significantly higher in Group 1 than in Group 2 (P < 0.001). By contrast, the [albumin]s - [albumin]a was significantly lower in Group 1 than in Group 2 (P < 0.001). None of these parameters was useful in differentiating the ascites of chronic liver disease from that of HCC. In this study, to differentiate malignant ascites from the ascites caused by liver diseases, [albumin]s - [albumin]a (< 1.5 g/dl) and the fibronectin level in the ascites (> 100 micrograms/ml) provided diagnostic accuracy (96.8% and 95.9%, respectively) as precise as those of the levels of albumin (> 1.6 g/dl), protein (> 2.5 g/dl), and lactate dehydrogenase (> 60 U/l; 97.9%, 96.7%, and 94.8%, respectively) in ascites. These results were better than that of carcinoembryonic antigen level (> 1.5 ng/ml, 80.9%).

CONCLUSIONS

The authors concluded that [albumin]s - [albumin]a offered the best method to survey malignant ascites because of its sensitivity (100%).

Various sonographic patterns of smooth muscle tumors of the gastrointestinal tract: a comparison with computed tomography

To evaluate the sonographic patterns of smooth muscle tumors of the gastrointestinal tract, we analyzed 25 patients with histologically confirmed smooth muscle tumors. Sonography revealed no abdominal mass in seven patients (sonogram-negative), and abdominal masses in 18 patients (sonogram-positive). The mean size of tumors in the sonogram-negative group (4.5 +/- 1.5 cm) was smaller than that in the sonogram-positive group (11.4 +/- 3.5 cm). We classified the various sonograms into three patterns. Comparing the sonograms with the computed tomographic pictures of each pattern, we theorized that the different patterns on sonograms may be caused by tumor necroses of different sizes with or without gas in the necrotic cavity. For the necrotic tumors, the size of the necrotic area did not correspond to the size of the tumor. However, the tumors with necroses were significantly larger than those without necroses. A central necrosis was found in cases exhibiting both leiomyosarcoma and leiomyoma. On comparing the sonogram-positive and sonogram-negative groups, we found that the size and location of a tumor may affect the detection rate of that tumor by sonography.

Interaction of natriuretic peptides and cGMP production via the same receptor in mouse astrocytes

Atrial and brain natriuretic peptides have been found previously to bind to specific receptors on cultured mouse astrocytes and to stimulate cyclic guanosine 5-monophosphate (cGMP) production with similar dose dependency although brain natriuretic peptide (BNP) shows a greater maximal stimulatory effect. The present study provides evidence that both peptides work through the same pathway. No additive or synergistic effect was observed when astrocytes were exposed to both peptides. However, human ANF(99-126) at high concentrations partially inhibited porcine BNP induced cGMP production to the level seen with ANF alone. ANF could be viewed as a partial agonist of pBNP competing for the same effector sites. Differences in structure between human ANF(99-126) and porcine BNP may account for the difference in cGMP response. The interaction between the two peptides and the cGMP response does not reflect receptor binding affinities and is likely to be a post-binding event.

Cardiovascular effects of substituted tetrahydroisoquinolines in rats

1. A series of substituted tetrahydroisoquinolins derived from the cleavage products of tetrandrine were found to inhibit [3H]-nitrendipine binding to rat cerebral cortical membranes. Those compounds which displaced [3H]-nitrendipine binding were also able to inhibit high KCl-induced contraction of rat aorta in vitro. 2. There was a significant correlation between the ability of these tetrahydroisoquinolines to inhibit [3H]-nitrendipine binding and KCl-induced contraction (r = 0.99, P less than 0.001). 3. CPU-23 (1-(1-[(6-methoxy)-naphth-2-yl])-propyl-2-(1-piperidine)-acetyl- 6,7- dimethoxy-1,2,3,4-tetrahydroisoquinoline), one of the most potent compounds identified in this series, behaved as a simple competitive inhibitor at the [3H]-nitrendipine binding site and reduced the apparent affinity but not the maximal number of binding sites in saturation analysis. 4. In contrast to nifedipine which caused hypotension and tachycardia, CPU-23 induced both hypotension and bradycardia in a dose-dependent manner in pentobarbitone-anaesthetized Sprague-Dawley rats, spontaneously hypertensive and age-matched normotensive WKY rats. 5. It is suggested that CPU-23 may exert its cardiovascular effects via interaction with the dihydropyridine binding site on the L-type calcium channel.

Activation of protein kinase C attenuates the cyclic GMP responses to C-type natriuretic peptide in cultured mouse astrocytes

C-type natriuretic peptide (CNP), a recently discovered natriuretic peptide, has a potent stimulatory effect on cyclic GMP (cGMP) formation in cultured mouse astrocytes. Pretreatment of astrocytes with phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), attenuated CNP-induced cGMP responses in a dose-dependent manner, with a half-maximal inhibitory concentration of 6 nM, whereas the inactive phorbol ester analog, 4 alpha-phorbol 12,13-didecanoate, was without effect. In the presence of staurosporine, a PKC inhibitor, the inhibitory effect of PMA on CNP-stimulated cGMP production was reversed. These results suggest that PKC is an inhibitory modulator of CNP-stimulated cGMP responses in astrocytes and that CNP may interact with neuropeptides which stimulate PKC.

Tachykinin-stimulated inositol phospholipid hydrolysis and taurine release from human astrocytoma cells

The activation of NK1 receptors on U373 MG human astrocytoma cells by substance P (SP) and related tachykinins was accompanied by an increase in taurine release and an accumulation of inositol phosphates. Both of these effects could be inhibited by spantide, a SP receptor antagonist. The relative potency of tachykinins in stimulating 3H-inositol phosphate accumulation correlated very well with their effects in stimulating the release of [3H]-taurine and inhibition 125I-Bolton-Hunter reagent-conjugated SP binding. The effect on [3H]taurine release was mimicked by a protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA). The inactive phorbol ester analogue 4-alpha-phorbol 12,13-didecanoate, however, was without effect. Both SP- and PMA-induced releases of [3H]-taurine were markedly inhibited by staurosporine, a potent PKC inhibitor. Pretreatment of U373 MG cells with 10 microM PMA for 19 h to down-regulate PKC activity also markedly inhibited both SP- and PMA-induced releases of [3H]-taurine. Treatment of cells with 100 nM SP induced a time-dependent translocation of PKC from the cytosolic fraction to the membrane fraction. These findings are consistent with the hypothesis that an activation of NK1 receptors on U373 MG cells results in the release of inositol phosphates and activation of PKC, which in turn may regulate the release of taurine.

C-type natriuretic peptide is a potent stimulator of cyclic GMP production in cultured mouse astrocytes

The effect of C-type natriuretic peptide (CNP), a novel member of the natriuretic peptide family, on cyclic GMP (cGMP) generation was studied in primary cultures of mouse astrocytes. CNP stimulated cGMP production by mouse astrocytes in a dose-dependent fashion, with an EC50 of 32 nM and a maximal stimulatory concentration of greater than 1 microM, which induced a rise of cGMP level from a baseline of 1.0 +/- 0.1 pmol/mg of protein to 196.2 +/- 22.0 pmol/mg of protein. Compared with our previously reported atrial and brain natriuretic peptide-induced cGMP responses, CNP had a lower EC50 and was 10-20 times more efficacious in its maximal effect on cGMP stimulation. These data lend support to the concept of a significant role of CNP in neuromodulation/neurotransmission.

Surgical management of subfoveal choroidal neovascularization

BACKGROUND

Subfoveal choroidal neovascularization (CNV) usually is associated with a poor visual prognosis. Laser photocoagulation of certain subfoveal membranes secondary to age-related macular degeneration (ARMD) appears preferable to observation based on recent Macular Photocoagulation Study (MPS) findings but is associated with decreased vision. The authors explored the use of vitreoretinal surgical techniques as an alternative method of eradicating subfoveal CNV.

METHODS

After vitrectomy, a small retinotomy technique was used to extract or disconnect from the choroidal circulation subfoveal CNV in 58 eyes. There were 33 eyes with ARMD, 20 eyes with presumed ocular histoplasmosis, and 5 eyes with miscellaneous etiologies. Five eyes also received subfoveal RPE patches.

RESULTS

With limited follow-up, significant improvement in vision (defined as 2 Snellen lines) was achieved in 7 of 22 eyes with ARMD CNV removal (1 eye 20/20), 0 of 4 eyes with ARMD CNV removal and RPE patches, and 1 of 7 eyes with ARMD CNV disconnection. Significant improvement was achieved in 6 of 16 eyes with presumed ocular histoplasmosis removal and 0 of 4 eyes with presumed ocular histoplasmosis CNV disconnection. In 5 eyes with miscellaneous CNV, 2 improved (20/20 and 20/40). CNV recurred in 29%.

CONCLUSIONS

Some patients with subfoveal CNV appear to benefit from surgical removal. Only rarely do eyes with ARMD improve. Longer-term follow-up and refined case selection are required before this approach can be widely recommended.

Guanine nucleotide-binding proteins in the intestinal parasite Giardia lamblia. Isolation of a gene encoding an approximately 20-kDa ADP-ribosylation factor

Giardia lamblia is a protozoan intestinal parasite that has characteristics of both eukaryotes and prokaryotes. To determine whether genes for guanine nucleotide-binding proteins are present in Giardia, genomic DNA and cDNA libraries were screened by polymerase chain reaction and by hybridization with mixed oligonucleotide probes complementary to sequences encoding conserved GTP-binding domains. A gene with a high degree of sequence identity with mammalian ADP-ribosylation factors (ARFs), believed to be important in vesicular transport, was identified. The Giardia ARF gene had a 573-base open reading frame encoding 191 amino acids which are 63-70% identical with known mammalian and yeast ARFs. Sequence conservation among ARFs was greatest in putative GTP-binding domains. A single ARF mRNA species of approximately 750 bases was found in two different Giardia isolates. Primer extension and RNA sequencing of the Giardia ARF transcript revealed a short (6-base) 5'-untranslated region similar in size to those found in other Giardia transcripts. Giardia extracts contained ARF activity, as shown by stimulation of cholera toxin-catalyzed ADP-ribosylation and a Giardia ARF expressed in Escherichia coli as a fusion protein likewise exhibited biochemical activity. Its presence in Giardia is consistent with the view that ARF emerged before the divergence of this protozoan from other eukaryotes (approximately 1.5 billion years ago), and that an ARF-like protein may have been the ancestor of several other classes of signal-transducing guanine nucleotide-binding proteins, including the alpha subunits of the heterotrimeric G proteins.