Solventogenic enzymes of Clostridium acetobutylicum: catalytic properties, genetic organization, and transcriptional regulation

The enzymes acetoacetate decarboxylase and coenzyme A transferase catalyse acetone production from acetoacetyl-CoA in Clostridium acetobutylicum. The adc gene encoding the former enzyme is organized in a monocistronic operon, while the ctf genes form a common transcription unit with the gene (adhE) encoding a probable polyfunctional aldehyde/alcohol dehydrogenase. This genetic arrangement could reflect physiological requirements at the onset of solventogenesis. In addition to AdhE, two butanol dehydrogenase isozymes and a thiolase are involved in butanol synthesis. RNA analyses showed a sequential order of induction for the different butanol dehydrogenase genes, indicating an in vivo function of BdhI in low level butanol formation. The physiological roles of AdhE and BdhII most likely involve high level butanol formation, with AdhE being responsible for the onset of solventogenesis and BdhII ensuring continued butanol production. Addition of methyl viologen results in artificially induced butanol synthesis which seems to be mediated by a still unknown set of enzymes. Although the signal that triggers the shift to solventogenesis has not yet been elucidated, recent investigations suggest a possible function of DNA supercoiling as a transcriptional sensor of the respective environmental stimuli.

Solventogenic enzymes of Clostridium acetobutylicum: catalytic properties, genetic organization, and transcriptional regulation

The enzymes acetoacetate decarboxylase and coenzyme A transferase catalyse acetone production from acetoacetyl-CoA in Clostridium acetobutylicum. The adc gene encoding the former enzyme is organized in a monocistronic operon, while the ctf genes form a common transcription unit with the gene (adhE) encoding a probable polyfunctional aldehyde/alcohol dehydrogenase. This genetic arrangement could reflect physiological requirements at the onset of solventogenesis. In addition to AdhE, two butanol dehydrogenase isozymes and a thiolase are involved in butanol synthesis. RNA analyses showed a sequential order of induction for the different butanol dehydrogenase genes, indicating an in vivo function of BdhI in low level butanol formation. The physiological roles of AdhE and BdhII most likely involve high level butanol formation, with AdhE being responsible for the onset of solventogenesis and BdhII ensuring continued butanol production. Addition of methyl viologen results in artificially induced butanol synthesis which seems to be mediated by a still unknown set of enzymes. Although the signal that triggers the shift to solventogenesis has not yet been elucidated, recent investigations suggest a possible function of DNA supercoiling as a transcriptional sensor of the respective environmental stimuli.

Tryptase and histamine release due to a sting challenge in bee venom allergic patients treated successfully or unsuccessfully with hyposensitization

BACKGROUND

Hyposensitization with been venom leads to full protection in most, but not all patients with IgE-mediated systemic reactions to bee stings.

OBJECTIVE

To determine the relationship of clinical reactivity to the release of mediators and to changes of antibody concentrations in the peripheral circulation at a bee sting challenge test.

METHODS

Blood was sampled before (1 min) and at 15, 60 and 180 min after a sting challenge from 19 patients on hyposensitization. Of these six still reacted and 13 were protected. Histamine, mast cell tryptase, bee venom-specific IgE and IgG in the serum, and histamine release from peripheral blood leucocytes (PBL) upon exposure to bee venom were determined.

RESULTS

Tryptase above the detection level was found only at 15 (60) min in 4/6 (1/6) patients who reacted. After the sting challenge there was a significant increase of the histamine levels in patients who reacted at 15 min (P < 0.05) and in patients who did react at 60 and 180 min (P < 0.01). The total histamine content of PBL was significantly decreased after 15 and 60 min in patients who reacted (P < 0.01) and in those that did not (P < 0.05). Bee venom-induced histamine release was significantly reduced in patients reacting and those that did not at 15 min (P < 0.05), and was significantly decreased in reactors also at 60 and 180 min (P < 0.05/0.01). Specific IgG antibodies showed a minor decrease (P < 0.05) after the sting challenge in both groups, whereas specific IgE did not change significantly.

CONCLUSION

These results indicate that bee venom anaphylaxis is associated with the release of mediators from both mast cells as well as basophils. Successful hyposensitization does not induce a state of immunological non-reactivity, but rather alters the magnitude and the pattern of mediator release.

Increased thrombin generation during fibrinogen and platelet recovery as an explanation for hypercoagulability in children with L-asparaginase therapy for ALL or NHL: a preliminary report

Three out of 21 patients treated at the Children's Hospital of Eastern Switzerland for ALL or NHL with the respective BFM-90 protocols experienced thrombotic complications during Erwinia L-asparaginase therapy. We therefore investigated the development of the haemostatic imbalance in six children during the induction phase of both protocols. In the average, elevated thrombin generation was found simultaneously to an increase in fibrinogen, cross-linked fibrin degradation products and platelet counts between protocol days 28 to 35. This period thus seems to harbour an increased potential of hypercoagulability which could explain the accumulation of thrombotic complications described by Sutor et al. Moreover, day to day investigations just before and one day after L-asparaginase administration did not show any relevant change in the above named parameters, thus rather indicating a cumulative than a single dose effect of Erwinia L-asparaginase therapy on the coagulation system. These findings lead to the question if the prophylactic use of anticoagulants might reduce the hypercoagulability seen during L-asparaginase therapy, which is currently under investigation in our institutions.

[Dyskeratosis congenita in monozygous twins]

Dyskeratosis congenita (DC) is a very rare form of genodermatosis with variable manifestations, which mainly affects male patients. The main clinical symptoms are poikilodermia, nail dystrophy and leucoplakia; there are many other cutaneous and systemic symptoms. To avoid complications and improve the prognosis early diagnosis and regular close surveillance of the patients are important. We report on 13-year-old monozygotic twin brothers who, in addition to the typical symptoms, had increased vulnerability of the skin, scarring of the hands and atrophy of the oral mucosa as well as splenomegaly, pancytopenia with severe aplasia of bone marrow and aseptic necrosis of the hip. The two brothers had nearly synchronous clinical manifestation and progression. This paper reviews the clinical symptoms, pathogenesis, differential diagnosis and genetic aspects of DC.