Codon usage, transfer RNA availability and mistranslation in amino acid starved bacteria

The fidelity of codon reading was examined in amino acid starved Escherichia coli. In one case the level of misincorporation of methionine was measured at an isoleucine residue encoded by either the commonly used AUU codon or the rarely used AUA codon. In this situation we found the frequency of methionine misincorporation to be very low and to be unaffected by the identity of the isoleucine codon. In other experiments histidine misincorporation for glutamine was measured in glutamine starved cells with normal levels of histidine-specific tRNA and cells overproducing this tRNA. Cells overproducing the tRNA had higher levels of misincorporation.

[An analysis of 30 cases of chylothorax and chyloperitoneum]

Thirty patients diagnosed as chylothorax and chyloperitoneum (13 of chylothorax, 9 of chyloperitoneum and 8 of both) in PUMC Hospital from 1923 to 1989 were reported. Thus, the incidence rate of these two diseases is rather low. The commonest causes were iatrogenic trauma (9 cases) and malignant tumor (7 cases). Other causes were tuberculosis (5 cases), lymphangioma (2 cases), Behcet's syndrome (1 case) and non-iatrogenic trauma (1 case). The etiology was not known in 5 cases. Acute episode was observed in patients with traumatic chylous effusion; it was usually manifested as dyspnea or abdominal distention. Patients with nontraumatic chylous effusion usually run a chronic course. The characteristics of chylous effusion were analyzed. Lymphangiography and lymphoscintigraphy with 99m TC-labeled dextran play important roles in diagnosis and treatment. It has been suggested that the changes in T-cell immunocompetence is important in determining whether the treatment should be conservative or operative. If chylous effusion is due to tuberculosis, antituberculosis treatment should be instituted.

[Lymphomatoid granulomatosis. A report of 2 cases]

Two patients with lymphomatoid granulomatosis were diagnosed by postmortem autopsy or exploratory thoracotomy. The lung, skin, spleen, renal and lymph nodes were involved. The most common presenting complaints are fever, cough, expectoration shortness of breath. The radiographic manifestations are multiple, bilateral nodular shadows. The histologic features is a unique form of pulmonary angiitis and granulomatosis, which is a necrotizing angiocentric and angio-destructive infiltrative process composed of small lymphocytes and atypical lymphoreticular cells.

Impact on catalysis of secondary structural manipulation of the alpha C-helix of Escherichia coli dihydrofolate reductase

The alpha C-helix of Escherichia coli dihydrofolate reductase has been converted to its counterpart in Lactobacillus casei by a triple mutation in the helix (H45R, W47Y, and I50F). These changes result in a 2-fold increase in the steady-state reaction rate (kcat = 26 s-1) that is limited by an increased off rate for the release of tetrahydrofolate (koff = 40 s-1 versus 12 s-1). On the other hand the mutant protein exhibits a 10-fold increase in the KM value (6.8 microM) for dihydrofolate and a 10-fold decrease in the rate of hydride transfer (85 s-1) from NADPH to dihydrofolate. The elevated rate of tetrahydrofolate release upon the rebinding of NADPH, a characteristic of the wild-type enzyme-catalyzed reaction, is diminished. The intrinsic pKa (6.4) of the mutant enzyme binary complex with NADPH is similar to that of the wild type, but the pKa of the ternary complex is increased to 7.3, about on pH unit higher than the wild-type value. Further mutagenesis (G51P and an insertion of K52) was conducted to incorporate a hairpin turn unique to the C-terminus of the alpha C-helix of the L. casei enzyme in order to adjust a possible dislocation of the new helix. The resultant pentamutant enzyme shows restoration of many of the kinetic parameters, such as kcat (12 s-1), KM (1.1 microM for dihydrofolate), and khyd (526 s-1), to the wild-type values. The synergism in the product release is also largely restored. A substrate-induced conformational change responsible for the fine tuning of the catalytic process was found to be associated with the newly installed hairpin structure. The Asp27 residue of the mutant enzyme was found to be reprotonated before tetrahydrofolate release.

A prospective study of nosocomial infections in cardiac surgery patients in China

A prospective survey of postoperative nosocomial infections (NI) in cardiac surgery was carried out in a cardiovascular specialty hospital in Beijing, China. During the period from December 1986 to December 1987, 1208 cardiovascular surgery patients were surveyed for NI. The overall incidence of NI was found to be 7.5%. The incidence of lower respiratory tract and wound infections were 4.5% and 2.9%, respectively. These two kinds of infection accounted for 78.1% of the total infections. After effective control measures were taken at the end of the first 6 months (December 1986 to May 1987) of the study, the incidence fell from 10.6% to 5.1% in the next 7-month period (June to December 1987). The pathogens causing NI were mostly gram-negative bacteria, and they were mainly opportunistic. The contribution of fungal infection was significant in the hospitals. The majority of the pathogenic isolates were highly resistant to the antibiotics commonly used in the hospital.

[Clinical analysis of 90 cases of eosinophilia and pulmonary infiltrates with peripheral eosinophilia]

90 patients diagnosed as eosinophilia and pulmonary infiltrates with peripheral eosinophilia in PUMC Hospital from 1957 to 1986 were reported. The cause of the eosinophilia was unknown in 42% of the patients. Among these patients, hypereosinophilic syndromes (HES) were suspected in 11 patients. The most common presenting symptoms of HES were fever, skin lesions gastrointestinal symptoms and hepatosplenomegaly, the mean peripheral blood eosinophil count was as high as 25.6 x 10(9) cells/L. Biopsies of bone marrow and involved organs revealed extensive eosinophilic infiltration and severe necrosis. In the past ten years, eosinophilia and pulmonary infiltrates caused by parasitic infections obviously decreased. The most common parasites were ascaris Lumbricoides, Ancylostoma duodenale and Clonorchis sinesis. The other main causes which induced pulmonary infiltrates were allergic bronchopulmonary mycosis (ABPM) and chronic eosinophilic pneumonia. The prevalence of ABPM increased recently; early diagnosis and effective therapy could prevent the irreversible damage resulting in airways obstruction and fibrosis.

Economic effects of nosocomial infections in cardiac surgery

A study of 60 infected patients and matched controls showed that nosocomial infection in cardiac surgery cost each patient an additional 2207 yuan (pounds 290). The cost of multisite infection was much higher. Infected patients were in hospital for a mean of 14 extra days.

[Mesothelioma and mesothelial hyperplasia]

Twenty cases of pleural mesothelioma (2 localized and 18 diffuse malignant pleural mesothelioma), 6 cases of diffuse malignant peritoneal mesothelioma and 1 case of mesothelial hyperplasia were reported. The prominent clinical manifestations of malignant mesothelioma was serosal effusion. The exudate was bloody, mucinous and of high specific gravity. It contained numerous mesothelial cells. The diagnosis is difficult because mesothelial hyperplasia and other malignant tumors may mimic mesothelioma in some clinical aspects. Roentgenography, CT scan, cytology of serosal fluid and biopsy world help to establish the diagnosis of mesothelioma. Immunohistochemical features of 4 cases of mesothelioma is negative immunostaining for carcino embryonic antigen (CEA) and positive for keratin antigen. In one case ultrastructural examination showed characteristic features of epithelial mesothelioma cells. The average survival period in case of chemotherapy and/or surgical intervention in patients of this series was 31.3 months. Mesothelial hyperplasia has rather good prognosis; but the strategy of therapy may be conservative.

[Diagnosis of cyanosis and digital clubbing caused by liver cirrhosis]

Six cases of cyanosis and digital clubbing caused by liver cirrhosis were reported. The mean levels of PaO2 and PaCO2 were 6.4 +/- 0.8 kPa (48.3 +/- 6.2 mmHg) and 3.9 +/- 0.8 kPa (29.5 +/- 6.1 mmHg) respectively. The cause of cyanosis and digital clubbing in liver cirrhosis was discussed. Abnormal intrapulmonary shunting (IPS), which was proved in 4 cases by whole-body radionuclide scanning with 99mTc-MAA, is suggested as the major cause of cyanosis in liver cirrhosis. Clinically IPS is usually associated with debilitating conditions characterized by hyperventilation, abnormality of lung diffusion and orthodeoxia or platypnea. The authors suggest that whole-body radionuclide scanning with 99mTc-MAA may be performed for establishing IPS if liver cirrhosis is highly suspected to be the cause of severe hypoxemia.

[Congenital pulmonary arteriovenous fistula. A report of 8 cases]

In 8 cases of A-V fistula the clinical manifestations were found to be exertional cyanosis, dyspnea and digital clubbing. Those patients might also have chest pain, tachycardia, telangiectases, polycythemia and severe hypoxemia. Murmur might be found over the surface area of the lesion. Chest X-ray examination revealed solitary circumscribed lesion in five of them and multiple lesions in two. X-ray findings were similar to bronchiectasis in one. The diagnosis and differential diagnosis of this lesion were discussed. Lung scan with technetium macroaggregated albumin was used to detect the A-V fistulae. Six cases were operated on and successful resections of the lesions were carried out in 4. One died right after the operation. In one case the larger fistula was resected, but some smaller fistulae remained and finally therapeutic embolization was carried out. No complication was encountered.

Pharmacological study of an irreversible partial agonist of opiate receptors, A-alpha-CAO

A-alpha-CAO induces weak analgesia with very short duration in mice and is able to antagonize the analgesic effect of morphine (Mor) up to 3-4 days after a single injection. No tendency of dependence has been observed. It acts as a partial agonist on MVD with Ke value of 9 X 10(-9) mol/L. Its antagonist effect remains after several washes and its agonist effect cannot be reversed by naloxone (Nx), provided the incubation time or the concentration of the agent is sufficient. On isolated GPI, A-alpha-CAO is a pure agonist with IC50 of 5.7 X 10(-10) mol/L; this agonist effect cannot be removed by washing but can be reversed by Nx. On RVD and RbVD, it has antagonist effect against beta-endorphine (beta-end) and U50488H, which cannot be washed out easily, and the pA2 are 7.5 and 7.6 respectively. A-alpha-CAO also inhibits the specific binding of 3H-etorphine (3H-Etor) to the P2 fraction of the mouse brain membrane with an IC50 of 3.2 X 10(-9) mol/L. The inhibition on the high affinity binding sites of 3H-Etor remains 95% even after 6 washes.

[Irreversible action of the opioid agonist alpha-CAM and its reaction with SH groups at opioid receptor binding sites]

7 alpha-Bis (beta-chloroethyl)amino-methyl-6,14-endoethenotetrahydrooripavine (alpha-CAM) was found to bind to opioid receptors irreversibly and react directly with sulfhydryl (SH) groups in P2 preparations of rat brain. The P2 preparations were pretreated as follows: protection of the SH groups at the opioid receptor binding sites by morphine or etorphine, and inactivation of the SH groups outside the binding sites by N-ethylmaleimide (NEM), followed by removal of the morphine or etorphine by washing. alpha-CAM was still able to bind the pretreated P2 preparations in an irreversible manner. The results indicate that the formation of covalent bonds between alpha-CAM and the SH groups of opioid receptor binding sites is possibly one of the biochemical mechanisms of the irreversible action of alpha-CAM.

Study of the 5-oxoprolinase reaction by 13C NMR

5-Oxoprolinase catalyzes the ATP-dependent decyclization of 5-oxo-L-proline to L-glutamate. Previous studies provided evidence for the intermediate formation of a phosphorylated form of 5-oxoproline (Seddon, A. P., and Meister, A. (1986) J. Biol. Chem. 261, 11538-11541) and of a tetrahedral intermediate (Li, L., Seddon, A. P., and Meister, A. (1987) J. Biol. Chem. 262, 11020-11025). A new approach to the study of the reaction mechanism using the 18O isotope effect on the 13C NMR signals for 5-oxoproline and glutamate is reported here. The 13C chemical shifts induced by 18O substitution for the carbonyl group of 5-oxoproline and the gamma-carboxyl group of glutamate are about 0.03 ppm with respect to the corresponding 16O-compounds. Using 5-[18O]oxo[5-13C]proline (97 and 79.5 atom % excess, 13C and 18O, respectively), the disappearance of the 18O-labeled and unlabeled 5-oxoproline and formation of the corresponding glutamate species were followed in the reactions catalyzed by purified preparations of 5-oxoprolinase isolated from Pseudomonas putida and from rat kidney. This procedure permits simultaneous determinations of the rates of 18O exchange and of the overall decyclization reaction. The ratios of 18O exchange rates to the overall reaction rates for the bacterial and kidney enzyme catalyzed-reactions were 0.28 and 0.14, respectively. The findings support the view that the coupling of ATP hydrolysis to 5-oxoproline decyclization involves formation of a phosphorylated tetrahedal intermediate. Although the exchange phenomena are consistent with the mechanistic interpretations, they seem not to be required for catalysis.

[Nonmalignant lymphoid disorders of the chest: a report of 4 cases with a review of literature]

The lung parenchyma, the mediastinal or hilar lymph nodes were involved by several nonmalignant lymphoid disorders which are not specific infections or malignant neoplasm. The etiology of these disorders remains unknown. They may be the outcome of viral-autoimmune causes or some chronic stimulation of the reticuloendothelial system by unknown antigens. Pulmonary pseudolymphoma is a localized pulmonary disease, generally not accompanied by lymph node enlargement or pleural effusion. However, lymph nodes of the mediastinum and hilum are involved in case of giant lymph node hyperplasia and angioimmunoblastic lymphadenopathy. An awareness of the differentiation of these reactive disorders from lymphoma is important because the radiological, clinical and laboratory manifestations may be similar. Final diagnosis must be based on the histological findings, Pulmonary biopsy or lymph node biopsy is always necessary. Adequate amount of biopsied tissue is required for better identification. Immunoperoxidase staining has been proposed to help the study of these conditions.

Spermatogenic cell-somatic cell interactions are required for maintenance of spermatogenic cell glutathione

Sertoli cells play a major role in the regulation of spermatogenic cell energy metabolism and differentiation. This study demonstrates that Sertoli cells are essential for the maintenance of spermatogenic cell glutathione (GSH), an important intracellular reductant and detoxicant. Primary spermatocytes and round spermatids isolated from Xenopus laevis contained 1.5 +/- 0.1 mM GSH, but sperm lacked detectable GSH. During a 5-day culture period, isolated spermatocytes and spermatids lost 80% of the initial GSH (t 1/2 = 55 h). The levels of GSH were unaffected by L-buthionine-SR-sulfoximine (BSO), a selective inhibitor of GSH synthesis. Cultures of testicular lobules and spermatocysts (composed of germ cells and Sertoli cells) depleted of interstitial tissue lost only 30% of their initial GSH in 4.5 days; the GSH levels decreased during treatment with BSO. Spermatogenic cells in cultured testes maintained their GSH levels for 7 days by a BSO-sensitive mechanism. These results demonstrate that the intracellular GSH levels of spermatogenic cells are dependent upon germ cell-somatic cell interactions. Spermatogenic cells were shown to possess gamma-glutamyl transpeptidase, glutathione synthetase, 5-oxoprolinase, and gamma-glutamylcysteine synthetase activities. [35S] Cysteine incorporation and distribution as analyzed by high performance liquid chromatography (HPLC) showed that isolated spermatogenic cells are capable of GSH synthesis. The rate of GSH synthesis, however, was insufficient to compensate for GSH turnover. These results demonstrate that production of spermatogenic cell GSH is dependent upon Sertoli cells. To our knowledge, this is the first evidence that interactions between different cell types may be of significance in GSH metabolism.

Structural analysis of a rat renal kallikrein gene

A renal kallikrein gene has been isolated, sequenced and characterized from a rat genomic library using a kallikrein cDNA probe. The kallikrein gene is 4160 bases in length and consists of 5 exons and 4 introns. The deduced sequence of the gene encodes an 18 amino acid (a.a.) signal peptide, a 6 a.a. propeptide and a 237 a.a. active enzyme with an N-terminal valine. A sequence comparison of this and tissue kallikrein (pancreatic kallikrein) indicates the key a.a. residues for serine protease activity (HIS-ASP-SER) and cleavage specificity at basic a.a. Northern blot analysis using a specific oligonucleotide probe reveals that this gene is expressed specifically in the kidney but not in the pancreas. This gene is also expressed non-specifically in the submandibular gland which expresses all kallikrein family genes. The expression of this kidney-specific kallikrein gene is regulated by steroid hormones.

Interaction of the protein components of 5-oxoprolinase. Substrate-dependent enzyme complex formation

5-Oxo-L-prolinase from Pseudomonas putida is composed of two reversibly dissociable proteins: Component A catalyzes 5-oxoproline-dependent cleavage of ATP, but does not catalyze the decyclization of 5-oxoproline; Component B is required for the coupling of ATP cleavage to ring-opening of 5-oxoproline to form glutamate (Seddon, A. P., Li, L., and Meister, A. (1984) J. Biol. Chem. 259, 8091-8094). We describe here the purifications of Components A and B to apparent homogeneity and the interactions between these two proteins. The cellular content of Component B activity is significantly greater than that of Component A. By gel filtration, Component A is a hexamer; but in the presence of substrates, it is a dimer. Component B can exist as an aggregate, an octamer, or a tetramer, depending upon the conditions used. Gel filtration of a mixture of Components A and B in the presence of substrates gives a unique protein species that exhibits 5-oxoprolinase activity. The Mr of this Component A-Component B complex indicates that it probably has an A2-B2 structure. The molar ratio of Component A to Component B in the complex was determined to be 1:1 by the continuous variation method (Job). Titrations of each component by the other suggest that phosphorylated 5-oxoproline-bound Component A is the entity that interacts with Component B. These studies indicate that the binding of phosphorylated 5-oxoproline-bound Component A to Component B to form a complex proceeds by a cooperative type mechanism. This is supported by the observed shifts of the intersection points of the Job curves (see Appendix).

18O studies on the 5-oxoprolinase reaction. Evidence for a phosphorylated tetrahedral intermediate

5-Oxoprolinase catalyzes a reaction in which the cleavage of ATP to ADP and Pi and the decyclization of 5-oxoproline to form glutamate are coupled. When the reaction catalyzed by 5-oxoprolinase of Pseudomonas putida was carried out to 90% completion in H2(18)O, the residual 5-oxoproline was found to contain 18O in the amide carbonyl oxygen atom. Such isotopic incorporation was not observed in similar studies with a subunit of the enzyme which catalyzes 5-oxoproline-dependent ATPase and formation of a phosphorylated 5-oxoproline intermediate (Seddon, A.P., and Meister, A. (1986) J. Biol. Chem. 261, 11538-11543). When the complete reaction was carried out in H2(18)O, the products glutamate (gamma-carboxyl) and inorganic phosphate were mono- and di-labeled with 18O. Studies with 5-[18O]oxo-L-proline confirmed such replacement of the oxygen atoms of the gamma-carboxyl group of glutamate and the carbonyl oxygen of 5-oxoproline. Oxygen was not transferred from 5-oxoproline to inorganic phosphate. Studies with analogs of 5-oxoproline showed that di-labeling of inorganic phosphate occurred only when ATP hydrolysis was coupled or partially coupled with the decyclization of the substrate. Studies with 5-oxoprolinase from rat kidney gave similar results. These observations are in accord with the view that the reaction involves enzyme-bound phosphorylated intermediates and provide evidence for a phosphorylated tetrahedral intermediate, whose formation is required for coupling.