Non-cirrhotic portal fibrosis in children

BACKGROUND AND OBJECTIVES

Non-cirrhotic portal fibrosis (NCPF) is an infrequent cause of portal hypertension in children. We report 11 children with NCPF, from among 338 with portal hypertension, seen over 6.5 years.

METHODS

The diagnosis was based on patent splenoportal axis on ultrasonography and/or splenoportal venography and liver biopsy showing no evidence of cirrhosis or other diagnosis, in children with portal hypertension. Those with variceal bleed were managed with endoscopic sclerotherapy and/or shunt surgery.

RESULTS

The median age was 11 years (range 5 to 14), and 8 were boys. Presentation was with variceal bleed in 6, lump in left upper abdomen in 5 (though all children had splenomegaly) and esophageal varices on endoscopy. The median spleen enlargement was 8.5 cm; 8 also had hepatomegaly. Hypersplenism was present in 7, and two had developed ascites after bleed. Of 6 children presenting with bleed, variceal obliteration was achieved on sclerotherapy (average 5.6 sessions) in 4 while two underwent shunt surgery for associated hypersplenism. After median follow up of 57.5 months (range 12-78) all are alive and well.

CONCLUSION

NCPF is an uncommon cause of portal hypertension in Indian children. Presentation with variceal bleed is less common than in adults; sclerotherapy is effective.

Enteropathogenic Escherichia coli isolates in paediatric diarrhoea

Enteropathogenic Escherichia coli (EPEC) are known to cause infantile enteritis. We studied the prevalence of EPEC in paediatric patients with acute and persistent diarrhoea. A total of 56 stool samples from paediatric patients were studied. There were 28 significant bacterial isolates. Of these 21 were untypable E. coli, 5 were typable E. coli, four of which belonged to members considered to be enteropathogenic. Non E. coli isolates grown in pure culture were one each of Pseudomonas aeruginosa and Citrobacter freundi. The study reveals the definitive role of EPEC in childhood diarrhoea at all age groups and emphasizes the need for characterisation of all significant E. coli isolates in this age group.

Pleural involvement by Salmonella senftenberg: a report of two cases

Non-typhoidal serovars of salmonella are an unusual cause of pleuropulmonary infections. We report two patients with empyema caused by Salmonella senftenberg. One patient had associated diabetes and gall bladder carcinoma, and infection was acquired in hospital. Both patients responded well to parenteral antibiotics.

Structure-activity relationship of piperine and its synthetic analogues for their inhibitory potentials of rat hepatic microsomal constitutive and inducible cytochrome P450 activities

Inhibitors of drug metabolism have important implications in pharmaco-toxicology and agriculture. We have reported earlier that piperine, a major alkaloid of black and long peppers inhibits both constitutive and inducible cytochrome P450 (CYP)-dependent drug metabolising enzymes. In the present study, an attempt has been made to prepare several novel synthetic analogues so as to relate various modifications in the parent molecule to the inhibition of CYP activities. Two types of mono-oxygenase reactions arylhydrocarbon hydroxylase (AHH) and 7-methoxycoumarin-O-demethylase (MOCD) have been studied. Inhibition studies were investigated in rat microsomal fraction prepared from untreated, 3MC- and PB- treated rat liver in vitro. Modifications were introduced into the piperine molecule: (i) in the phenyl nucleus, (ii) in the side chain and (iii) in the basic moiety. Thus, 38 compounds have been subjected to such studies, and simultaneously an attempt has also been made to arrive at the structure-activity relationship of synthetic analogues. In general, most of the inhibitory potential of the parent molecule is lost with modification in either of the three components of piperine. Saturation of the side chain resulted in significantly enhanced inhibition of CYP while modifications in the phenyl and basic moieties in few analogues offered maximal selectivity in inhibiting either constitutive or inducible CYP activities. Thus few novel analogues as CYP inactivators have been synthesized which may have important consequences in pharmacokinetics and bioavailability of drugs.

Diagnostic value of push-type enteroscopy: a report from India

OBJECTIVE

We sought to assess the diagnostic value of push-type enteroscopy in relation to indications.

METHODS

Ninety-nine consecutive patients (mean age, 42+/-15 yr; 65 men) with suspected small bowel disorders underwent push enteroscopy. The indications were chronic diarrhea (n = 54), obscure gastrointestinal (GI) bleeding (n = 21), abdominal pain (n = 10), abnormal radiological studies of small bowel (n = 5), iron deficiency anemia (n = 5), and others (n = 4). Push enteroscopy was performed using the Olympus SIF-10 (160-cm) enteroscope.

RESULTS

Endoscopic examination of the jejunum was successful in all the patients, except one with a distal duodenal stricture. The length of the jejunum examined ranged from 10 to 70 cm. The time taken to complete the procedure varied from 2 to 30 min. Lesions were found in nine (42.8%) patients with obscure GI bleeding; six (28.5%) had worms (Ascaris lumbricoides [n = 3], Ankylostoma duodenale [n = 3]) in the jejunum, producing multiple erosions and bleeding points. In the chronic diarrhea group, a diagnosis was made in 13 (24%) patients on enteroscopic visualization and jejunal histology: celiac disease (n = 6), tropical sprue (n = 3), Crohn's disease (n = 1), secondary lymphangiectasia (n = 1), strongyloidiasis (n = 1), and nodular lymphoid hyperplasia with giardiasis (n = 1). In patients with abdominal pain, enteroscopy provided a diagnosis in one (10%) patient. No positive diagnosis could be made on enteroscopy in patients with iron deficiency anemia and abnormal radiological studies of small bowel.

CONCLUSION

Push-type enteroscopy is a useful test in the evaluation of patients with obscure GI bleeding and chronic diarrhea. In developing countries, in patients with obscure GI bleeding, the presence of worms in the jejunum is an important finding on enteroscopy. Tropical sprue, giardiasis, and strongyloidiasis are distinct findings in patients with chronic diarrhea in the present series.

Reaction between 8-Hydroxyquinoline and Salicylic Acid in Solid State and Solution

8-Hydroxyquinoline reacts with salicylic acid both in solid state and solution forming a yellow coloured compound. Phase diagram studies have shown the formation of a 1:1 addition compound stable in solid state and dissociated in solution. Differential thermal studies have shown that the reaction products obtained from solution and solid state reaction are almost identical except that there is a possibility of entrapped solvent molecules when the product was prepared from benzene. Also the reaction product shows a thermochromic effect. X-ray diffraction studies have revealed some structural difference between the reaction product obtained from solution and solid state reaction. Spectroscopic studies show the possibility of hydrogen bonding in the reaction product.

The reaction in the solid state is slow and once a thin layer of reaction product is formed at the surface of salicylic acid crystals, the reaction rate becomes practically negligible. This may be due to the compactness of the product layer and unfavourable crystal packing in to the crystal lattice of salicylic acid. Microstructural studies have shown that there are structural changes during solid state reaction.

Diagnostic value of push-type enteroscopy: a report from India

OBJECTIVE

We sought to assess the diagnostic value of push-type enteroscopy in relation to indications.

METHODS

Ninety-nine consecutive patients (mean age, 42+/-15 yr; 65 men) with suspected small bowel disorders underwent push enteroscopy. The indications were chronic diarrhea (n = 54), obscure gastrointestinal (GI) bleeding (n = 21), abdominal pain (n = 10), abnormal radiological studies of small bowel (n = 5), iron deficiency anemia (n = 5), and others (n = 4). Push enteroscopy was performed using the Olympus SIF-10 (160-cm) enteroscope.

RESULTS

Endoscopic examination of the jejunum was successful in all the patients, except one with a distal duodenal stricture. The length of the jejunum examined ranged from 10 to 70 cm. The time taken to complete the procedure varied from 2 to 30 min. Lesions were found in nine (42.8%) patients with obscure GI bleeding; six (28.5%) had worms (Ascaris lumbricoides [n = 3], Ankylostoma duodenale [n = 3]) in the jejunum, producing multiple erosions and bleeding points. In the chronic diarrhea group, a diagnosis was made in 13 (24%) patients on enteroscopic visualization and jejunal histology: celiac disease (n = 6), tropical sprue (n = 3), Crohn's disease (n = 1), secondary lymphangiectasia (n = 1), strongyloidiasis (n = 1), and nodular lymphoid hyperplasia with giardiasis (n = 1). In patients with abdominal pain, enteroscopy provided a diagnosis in one (10%) patient. No positive diagnosis could be made on enteroscopy in patients with iron deficiency anemia and abnormal radiological studies of small bowel.

CONCLUSION

Push-type enteroscopy is a useful test in the evaluation of patients with obscure GI bleeding and chronic diarrhea. In developing countries, in patients with obscure GI bleeding, the presence of worms in the jejunum is an important finding on enteroscopy. Tropical sprue, giardiasis, and strongyloidiasis are distinct findings in patients with chronic diarrhea in the present series.

Congenital hepatic fibrosis in Indian children

BACKGROUND

Congenital hepatic fibrosis (CHF) is an uncommon cause of portal hypertension in children. So far, there is no report of this from the subcontinent. We have studied the clinical spectrum of CHF in North Indian children.

METHODS

Fifteen children were diagnosed with CHF on the basis of their liver histology over a period of 6.5 years. Their clinical details were recorded. Oesophagogastroduodenoscopy and abdominal ultrasonography were performed in all cases. All siblings were examined clinically; and ultrasonography, endoscopy and liver biopsy were performed if there was firm hepatomegaly. Children with variceal bleeding were managed by endoscopic sclerotherapy. The median age of these children was 8 years with a male to female ratio of 1.5:1.

RESULTS

Only one sibling (of 33) was diagnosed as having CHF. The predominant presentations were variceal bleeding in six, abdominal distension in seven and incidental detection of organomegaly in two. Hepatomegaly was present in all patients and splenomegaly in all but one. Liver function and renal function tests were normal in all children, except for a raised serum alkaline phosphatase in six. Two children had associated renal cysts, two had choledochal cysts, one each had Caroli's disease and biliary atresia and two children had portal vein thrombosis. Variceal obliteration was achieved in five children after an average 4.8 sclerotherapy sessions and one required a mesocaval shunt. On follow up (median 41 months, range 1-80 months) all are doing well.

CONCLUSIONS

Congenital hepatic fibrosis is mainly sporadic in India and associated renal lesions are uncommon. Endoscopic sclerotherapy is effective in controlling variceal bleed and the prognosis is universally good in the absence of renal diseases.

Fine-needle aspiration biopsy of orbital meningioma

Fine-needle aspiration was performed on an orbital mass in a 53-yr-old woman. The cytologic diagnosis was meningioma, which was later confirmed by histologic study of biopsy material. The cytologic features of the aspirated material (nuclear pseudoinclusions, psammoma bodies, and cells arranged in syncytial sheets and whorls) allowed a rapid, reliable, outpatient diagnosis to be formulated. The cytologic features are discussed and the literature is reviewed. Diagn. Cytopathol. 1999;21:402-404.

Opposing effects of beta(1)- and beta(2)-adrenergic receptors on cardiac myocyte apoptosis : role of a pertussis toxin-sensitive G protein

BACKGROUND

beta-Adrenergic receptor (beta-AR) stimulation increases apoptosis in adult rat cardiac (ventricular) myocytes (ARVMs) via activation of adenylyl cyclase. beta(2)-ARs may couple to a G(i)-mediated signaling pathway that can oppose the actions of adenylyl cyclase.

METHODS AND RESULTS

In ARVMs, beta-AR stimulation for 24 hours increased the number of apoptotic cells as measured by flow cytometry. beta-AR-stimulated apoptosis was abolished by the beta(1)-AR-selective antagonist CGP 20712A (P<0.05 versus beta-AR stimulation alone) but was potentiated by the beta(2)-AR-selective antagonist ICI 118,551 (P<0.05 versus beta-AR stimulation alone). The muscarinic agonist carbachol also prevented beta-AR-stimulated apoptosis (P<0.05 versus beta-AR stimulation alone), whereas pertussis toxin potentiated the apoptotic action of beta-AR stimulation (P<0.05 versus beta-AR stimulation alone) and prevented the antiapoptotic action of carbachol.

CONCLUSIONS

In ARVMs, stimulation of beta(1)-ARs increases apoptosis via a cAMP-dependent mechanism, whereas stimulation of beta(2)-ARs inhibits apoptosis via a G(i)-coupled pathway. These findings have implications for the pathophysiology and treatment of myocardial failure.

A lack of evidence for down-modulation of CD3 zeta expression in colorectal carcinoma and pregnancy using multiple detection methods

Loss of the T cell receptor-associated CD3 zeta chain has been proposed as a possible mechanism of the acquired immunosuppression in both tumour-bearing hosts, and in symptomatic patients with HIV infection. However, other reports suggest that the zeta-chain loss may in part be caused by protease activity of contaminating phagocytes ex vivo. Using flow cytometry and Western blot analysis on highly purified T cells, and ensuring adequate addition of protease inhibitors, we have studied the expression of CD3zeta on peripheral blood T cells from patients with colorectal carcinoma, and compared these with normal controls, and pregnant donors, as a further example of an immunocompromised state. Immunohistochemistry was performed on tumour sections from patients with colorectal carcinoma to measure CD3zeta expression in tumour infiltrating T cells, and compared with normal mucosa and tonsil. Using these three approaches, our data provide no evidence for downregulation of CD3zeta chain expression either in colorectal carcinoma or pregnancy and suggest that this explanation is unlikely to fully account for the reduced T cell function associated with these conditions in all patients.

Yeast colonisation & fungaemia in preterm neonates in a tertiary care centre

Seventy consecutive preterm neonates who stayed in the hospital for more than seven days between March and October 1996, were studied for colonisation at oral, umbilical, groin, and rectal areas and for fungaemia. Overall, 71.4 per cent of the neonates were colonised and colonisation occurred within 24 h in 38 per cent preterm neonates. Neonates weighing less than 1500 g were colonised more frequently at more than one site and had higher load of yeast. Candida albicans (19%), Pichia (Hansenula) anomala (17.5%), C. tropicalis (13.2%), C. parapsilosis (12.3%) and Trichosporon cutaneum (10.0%) were the predominant colonising yeasts. Fungaemia was detected in 22.8 per cent of preterm neonates with predominance of P. anomala fungaemia (62.5%). Prematurity, male sex, broad spectrum antibiotic therapy, intubation and higher colonising rate were identified as significant risk factors for development of fungaemia. Except one strain of C. tropicalis, all yeast strains were sensitive to commonly used systemic antifungal agents. Study highlights the importance of routine surveillance of yeast colonisation of preterm neonates with identifying possible risk factors.

Epidemiology, presentation and management of congenital muscular torticollis

AIM OF STUDY

Congenital muscular torticollis is a condition of debatable aetiology and management. Untreated, cervical function and facial cosmesis may be severely compromised. The aim of this study was to establish the epidemiology, presentation and management of congenital muscular torticollis in Singapore.

PATIENTS

Ninety-one patients with torticollis were seen at the National University Hospital (NUH) from January 1994 to December 1997. Torticollis was first noted at a median age of 2 months with the median age of presentation being 6 months. At presentation, a sternomastoid tumour was noted in 33 patients and 62 patients had facial asymmetry. Thirteen of 22 patients with neonatal records available had mandibular hypoplasia at birth on the side where the sternomastoid was affected. Half of the patients (45) had a right sided lesion, with 46 being left sided. The rates of assisted breech delivery, instrumental deliveries (forceps and vacuum) and Caesarean section were higher in the study group. Nine (59.1%) of 13 patients with vertex presentation, had a lesion on the side of the presenting shoulder. Forty-eight of 72 patients responded well to therapy with improvement; 20 underwent surgery and the median age of presentation of 19.5 months in this group was significantly later than that of 4 months in the group which responded to physiotherapy alone.

CONCLUSION

Birth trauma appears to be the main aetiological factor in congenital muscular torticollis. Patients generally respond well to physiotherapy. This study revealed 2 findings hitherto unreported: (1) mandibular hypoplasia may be an useful early sign of this condition, and (2) the side affected may depend on the side of shoulder delivered first. More studies, however, are required to confirm these findings.

Factors explaining the use of psychiatric services by general practices

BACKGROUND

Referral rates from general practitioners to hospital services vary up to 25-fold, and several studies have sought reasons for this apparent inconsistency in clinical practice. However, few studies have concentrated on, or indeed included, psychiatric patients or psychiatric referral rates.

AIM

To determine the effect of population, general practice, and mental health service factors on use of specialist mental health services by general practices.

METHOD

Cross-sectional data from computerized records used in managing clinical care on all patients aged 16 to 64 years who had been in contact with any mental health service staff over a two-year period. Twenty-three practices in Huntingdon Health District were studied, with a list population of 87,643 patients aged 16 to 64 years, served by one inpatient ward and three community mental health teams. The main outcome measures were the relation between age-standardized utilization ratio and markers of morbidity, deprivation, community mental health provision, and practice prescribing.

RESULTS

Variation between practices in the use of mental health services was relatively limited, especially compared with the use of other secondary medical and surgical services. Three factors together explained 60.8% of the variance in use between practices: a census-based index of long-term limiting illness in females registered with the practice, use of one of the three community mental health teams, and average quarterly defined daily doses of hypnotics prescribed per practice population. Relatively high prescribing of hypnotics was associated with lower service use.

CONCLUSION

Population morbidity and factors in the mental health service explain a substantial part of the variation in the use of mental health services between practices. Further work is needed to replicate these findings and explore why team factors and prescribing patterns influence utilization ratios. This study underlines the importance of examining population, practice, and specialist service factors in explaining variation in the use of secondary care by general practices.

Hepatoprotective activity of ellagic acid against carbon tetrachloride induced hepatotoxicity in rats

Administration of CCl4 to normal rats and consequent oral feeding with ellagic acid (50 mg/kg) provided a significant protection against the biochemical alterations in serum and liver produced by CCl4. In vitro experiments showed that liver microsomes from animals treated with ellagic acid and CCl4, decreased lipid peroxidation compared to microsome prepared from rats exposed to CCl4 alone.

Evacuation interval after vaginal misoprostol for preabortion cervical priming: a randomized trial

OBJECTIVE

To determine the optimal interval for evacuation after preabortion cervical priming with vaginal misoprostol.

METHODS

One hundred eighty healthy nulliparas requesting legal termination of pregnancy between 6 and 11 weeks' gestation were assigned randomly to receive 400, 600, or 800 microg of intravaginal misoprostol. Vacuum aspiration was done after 3 hours in the 400-microg group and after 2 hours in the 600- and 800-microg groups. The degree of cervical dilatation before operation was measured with a Hegar dilator. Preoperative and intraoperative blood loss and associated side effects were also assessed.

RESULTS

Eleven (18.3%) and 15 (25.0%) women in the 600-and 800-microg groups, respectively, had cervical dilatation of at least 8 mm after an interval of 2 hours; 55 (91.7%) women who received 400 microg for a 3-hour interval had similar cervical dilatation. Using 400 microg as a baseline, the odds ratio (OR) was 0.02; 95% confidence interval (CI) was 0.01, 0.06 for 600 microg and OR 0.03; 95% CI 0.01, 0.09 for 800 microg for achieving successful preabortion cervical dilatation of at least 8 mm. The mean cervical dilatation of 6.7 mm and 6.8 mm for the higher doses was also significantly less than that of 8.1 for the 400-microg dose (P<.001). The mean preoperative and intraoperative blood loss was only statistically different when the 400- and 800-microg groups were compared (P = .03). There were also significantly more side effects, namely abdominal pain and fever above 38.0 C, in the 600- and 800-microg groups (P<.001), compared with the 400-microg group. When the 600- and 800-microg groups were compared, there were still significantly more women complaining of abdominal pain (P<.001). None of the women in the study required analgesics for pain or antipyretics for fever.

CONCLUSION

The minimal evacuation interval should be at least 3 hours for successful preabortion cervical priming.

Medical treatment of a grossly enlarged adenomyotic uterus with the levonorgestrel-releasing intrauterine system

Adenomyosis is an important cause of menorrhagia. Besides hysterectomy, the treatment options for adenomyosis have been limited. Presented here is the successful treatment of adenomyosis in a woman presenting with menorrhagia, dysmenorrhea, and an enlarging uterus, for whom conservative therapy initiated with mefenamic acid was unsatisfactory. The patient had insertion of the levonorgestrel-releasing intrauterine system (LNG-IUS). A marked decrease in uterine size occurred within 12 months of insertion accompanied by resolution of the menorrhagia and dysmenorrhea. Thus, the LNG-IUS is a viable option and represents a real advance in the treatment of adenomyosis.

Protective effect of ellagic acid on t-butyl hydroperoxide induced lipid peroxidation in isolated rat hepatocytes

Ellagic acid, a plant polyphenol, showed protective effect on isolated rat hepatocytes against destruction due to lipid peroxide formation induced by t-butyl hydroperoxide in vitro. Ellagic acid inhibited the generation of superoxide anions and hydroxyl radicals both in enzymic and non enzymic systems, thus providing protection against oxidative damage.

Characterization of SiO2-Na2O-Fe2O3-CaO-P2O5-B2O3 glass ceramics

Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO2-Na2O-Fe2O3-CaO-P2O5-B2O3 system to find their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body fluids. The glass ceramic samples exhibit Na3CaSi3O8 and Na3-XFeXPO4 phases. After dipping the glass ceramic samples in simulated body fluids silica hydrogel first forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.

Effect of rotavirus infection on small gut pathophysiology in a mouse model

AIM

To study the effect of rotavirus infection on amino acid uptake in the small intestine in an experimental mouse model.

METHODS

Infant mice (7-8 days of age) were orally infected with the EB serotype 3 strain of rotavirus and animals (both infected and control) were killed on days 0, 1, 3, 5, 7 and 10 post inoculation (PI) after recording their bodyweights. Gamma-glutamyltranspeptidase (GGT), leucine amino peptidase (LAP), glutathione (GSH) and leucine amino acid uptake in the jejunum and ileum were assessed.

RESULTS

Infected animals showed significant reduction in their bodyweights and intestinal lengths on the third day PI compared with controls. Leucine amino peptidase, GGT, GSH and leucine uptake were significantly reduced in the ileum on the third and fifth day PI compared with controls while uptake in the jejunum was only reduced on third day PI. The LAP, GGTP, GSH and leucine uptake attained normal levels on the seventh day when diarrhoea stopped. Histology showed damage to the villi in the jejunum and prominent cytoplasmic vacuolation in the ileum of infected animals on the third and fifth day PI.

CONCLUSION

Rotavirus affects amino acid uptake in the small intestine at the time of peak infection.

Mandibulo-acral dysplasia: Indian patient with severe bony changes

We report an Indian patient with mandibulo-acral dysplasia. This patient had absence of spinous processes of 4th and 5th cervical vertebrae and very severe bony changes but no loss of teeth.

Inhibition of copper-zinc superoxide dismutase induces cell growth, hypertrophic phenotype, and apoptosis in neonatal rat cardiac myocytes in vitro

Oxidative stress has been implicated in the pathophysiology of myocardial failure. We tested the hypothesis that inhibition of endogenous antioxidant enzymes can regulate the phenotype of cardiac myocytes. Neonatal rat ventricular myocytes in vitro were exposed to diethyldithiocarbamic acid (DDC), an inhibitor of cytosolic (Cu, Zn) and extracellular superoxide dismutase (SOD). DDC inhibited SOD activity and increased intracellular superoxide in a concentration-dependent manner. A low concentration (1 micromol/L) of DDC stimulated myocyte growth, as demonstrated by increases in protein synthesis, cellular protein, prepro-atrial natriuretic peptide, and c-fos mRNAs and decreased sarcoplasmic reticulum Ca(2+)ATPase mRNA. These actions were all inhibited by the superoxide scavenger Tiron (4,5-dihydroxy-1,3-benzene disulfonic acid). Higher concentrations of DDC (100 micromol/L) stimulated myocyte apoptosis, as evidenced by DNA laddering, characteristic nuclear morphology, in situ terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL), and increased bax mRNA expression. DDC-stimulated apoptosis was inhibited by the SOD/catalase mimetic EUK-8. The growth and apoptotic effects of DDC were mimicked by superoxide generation with xanthine plus xanthine oxidase. Thus, increased intracellular superoxide resulting from inhibition of SOD causes activation of a growth program and apoptosis in cardiac myocytes. These findings support a role for oxidative stress in the pathogenesis of myocardial remodeling and failure.

Analysis of the role of glutamine 190 in the catalytic mechanism of murine leukemia virus reverse transcriptase

To determine the catalytic role of Gln(190), a member of the highly conserved LPQG motif in Moloney murine leukemia virus reverse transcriptase, we carried out site-directed mutagenesis of this residue to generate Q190N and Q190A. Both mutant proteins exhibited a significant loss in their polymerase and pyrophosphorolysis activities with a more pronounced effect noted with the Gln --> Asn substitution. The catalytic efficiencies of the mutants exhibited a 40-70-fold reduction with poly(rC) and poly(dC) templates in the presence of Mg(2+) and a 10-20-fold reduction with poly(rA) template in the presence of Mn(2+). Interestingly, the K(m) for NTP exhibited only a moderate 3-10-fold increase irrespective of the template-primer and the metal ion. Photoaffinity labeling of both the mutant and the WT enzymes exhibited an identical affinity for RNA.DNA and DNA.DNA template-primers. However, unlike the WT enzyme, the mutant enzymes exhibited a significantly reduced ability to catalyze the nucleotidyltransferase reaction on the covalently immobilized template-primer. An examination of the rate constants for the first and the second nucleotide for the mutant enzymes indicated dissimilar rates, indicating that Gln(190) may be involved in a rate-limiting, conformational change step both before and after the phosphodiester bond formation. Furthermore, the processivity of DNA synthesis by the mutant enzymes was decreased severely, which may result from the lower catalytic efficiency as well as translocation defect.