The presence of glutamate dehydrogenase is a selective advantage for the Cyanobacterium synechocystis sp. strain PCC 6803 under nonexponential growth conditions

The unicellular cyanobacterium Synechocystis sp. strain PCC 6803 has two putative pathways for ammonium assimilation: the glutamine synthetase-glutamate synthase cycle, which is the main one and is finely regulated by the nitrogen source; and a high NADP-dependent glutamate dehydrogenase activity (NADP-GDH) whose contribution to glutamate synthesis is uncertain. To investigate the role of the latter, we used two engineered mutants, one lacking and another overproducing NADP-GDH. No major disturbances in the regulation of nitrogen-assimilating enzymes or in amino acids pools were detected in the null mutant, but phycobiline content, a sensitive indicator of the nutritional state of cyanobacterial cells, was significantly reduced, indicating that NADP-GDH plays an auxiliary role in ammonium assimilation. This effect was already prominent in the initial phase of growth, although differences in growth rate between the wild type and the mutants were observed at this stage only at low light intensities. However, the null mutant was unable to sustain growth at the late stage of the culture at the point when the wild type showed the maximum NADP-GDH activity, and died faster in ammonium-containing medium. Overexpression of NADP-GDH improved culture proliferation under moderate ammonium concentrations. Competition experiments between the wild type and the null mutant confirmed that the presence of NADP-GDH confers a selective advantage to Synechocystis sp. strain PCC 6803 in late stages of growth.     

Abstinence is not the only answer

Familial inheritance of congenital diaphragmatic hernia is uncommon. We report two siblings with identical bilateral diaphragmatic defects.     

Markedly altered colchicine kinetics in a fatal intoxication: examination of contributing factors

1. Colchicine poisoning, which is relatively rare, is associated with significant morbidity and mortality. Whilst a new treatment modality, in the form of colchicine-specific Fab fragments is on the horizon, currently available therapy is largely supportive. 2. The elimination of colchicine occurs primarily by hepatic metabolism, following a first-order process, with significant enterohepatic circulation. Renal extraction is responsible for approximately 20% of colchicine elimination. 3. We report a case of colchicine intoxication, complicated by the presence of co-ingestants, in which serum colchicine concentrations remained quasi-constant over the 3 days of the patient's survival, consistent with marked alterations both in metabolism and excretion. The initial presentation was relatively benign but the subsequent course was one of severe colchicine poisoning, resulting in death. 4. Severe colchicine toxicity appears to have resulted in a vicious cycle of progressive organ dysfunction and impaired elimination. 5. Josamycin, one of the co-ingestants and an inhibitor of P-glycoprotein, the membrane pump responsible for multidrug resistance, may have played a significant role in impeding the cellular and biliary elimination of colchicine. Co-ingested opioid and anticholinergic compounds may have altered colchicine absorption and gastrointestinal transit. 6. This case serves as a reminder of the need for attention to co-ingested drugs, to early aggressive therapy, and if available, to consideration of immunotherapy.     

Computerized tomographic assessment of the composition of gallstones

We present the results of an in vitro study of biliary lithiasis (n = 106) with computerized tomography (CT). We analyzed the correlation between composition of gallstones (crystallographic analysis of thin sections and atomic absorption spectrophotometric analysis of total calcium content) with CT patterns (densitometry) and their corresponding attenuations. Six main CT patterns were distinguished: hypodense (homogeneous and heterogeneous), dense, homogeneous hyperdense, ringed hyperdense and irregular hyperdense. Statistically significant differences (p < 0.05) were found between attenuations for cholesterol (mixed and pure) and pigmentary stones. We found a good inverse correlation between attenuations and cholesterol content; the contents of pigment, inorganic calcic salts and total calcium content also showed significant direct correlations (p < or = 0.01). Of the samples classified as pure cholesterol type stones, 86.4% showed hypodense patterns, and the remaining 13.6% showed irregular hyperdense patterns. Of the pigmentary stones, 80% showed homogeneous hyperdense images. All stones that contained more than 3% calcium produced hyperdense patterns, whereas 72.4% of the stones that contained less calcium produced hypodense images. Tomodensitometric measurements provided more information than simple radiography, and made it possible to distinguish a greater variety of gallstone types based on structural complexity.     

Interaction of the two proteins of the methoxylation system involved in cephamycin C biosynthesis. Immunoaffinity, protein cross-linking, and fluorescence spectroscopy studies

Cephamycin C-producing microorganisms contain a two-protein enzyme system that converts cephalosporins to 7-methoxycephalosporins. Interaction between the two component proteins P7 (Mr 27,000) and P8 (Mr 32,000) has been studied by immunoaffinity chromatography using anti-P7 and anti-P8 antibodies, cross-linking with glutaraldehyde, and fluorescence spectroscopy analysis. Co-renaturation of the P7 and P8 polypeptides resulted in the formation of a protein complex with a molecular mass of 59 kDa, which corresponds to a heterodimer of P7 and P8. Glutaraldehyde cross-linking of the polypeptides after assembly of the protein complex showed the presence of a single heterodimer form that reacted with antibodies against P7 and P8. Each separate protein did not associate with itself into multimers. The P7.P8 complex co-purified by immunoaffinity chromatography from extracts of Nocardia lactamdurans and Streptomyces clavuligerus, suggesting that both proteins are present as an aggregate in vivo. Fluorescence spectroscopy studies of 5-methylaminonaphthalene-1-sulfonyl-P7 in response to increasing concentrations of P8 showed a blue shift in the fluorophore emission, indicating a conformational change of P7 in response to the interaction of P8 with an apparent dissociation constant of 47 microM. NADH showed affinity for the P7 component. The P7.P8 complex interacted strongly with the substrates S-adenosylmethionine and cephalosporin C, differently from that occurring with the separate P7 or P8 components, resulting in a strong blue shift in the fluorescence emission spectra of the complex.     

Healing in the gastrointestinal tract

Healing in the GI tract is rapid when free of complications: Unlike cutaneous healing, in which progress can be observed on a daily basis and intervention instituted early if necessary, healing of the intestinal anastomosis is anatomically obscured from inspection, allowing the surgeon only the patient's parameters of general well-being to judge the success of the operation. For the same reason, complications usually require re-operation, with the associated morbidity of a laparotomy and additional general anesthetic. This places a great responsibility on the surgeon to be cognizant of all the preoperative, intraoperative, and postoperative factors relating to anastomotic healing that might compromise the healing process. Bearing these in mind, along with attention to technical detail, should limit complications to an acceptable level. Patients most at risk are (1) those who perioperatively develop physiologic problems that lead to shock, hypoxia, and resultant anastomotic ischemia, (2) those with radiation-induced tissue injury, (3) those with sepsis, and (4) those with preoperative bowel obstruction. Malnourishment, malignancy, diabetes, steroids, and age also influence outcome to varying degrees. Future advancement in the field of GI healing lies in our ability to manipulate the early struggle between collagen synthesis and collagen breakdown. A profound understanding of the molecular and biochemical pathways and the factors that control them will bring us closer to this goal. Clinically, this may be accomplished by the introduction of wound healing enhancers into the anastomotic site, possibly by incorporating them into suture materials, biofragmentable anastomotic rings, or staple materials. Already much is known about the influence of different cytokines and growth factors on collagen regulation, knowledge that will help resolve many of the long-standing problems associated with GI surgery.