Biochemical and spectroscopic characterization of two new cytochromes isolated from Desulfuromonas acetoxidans.

The multimeric cytochromes described to date in sulfate- and sulfur-reducing bacteria are associated with diverse respiratory modes involving the use of elemental sulfur or oxidized sulfur compounds as terminal acceptors. They exhibit no structural similarity with the other cytochrome c classes and are characterized by a bis-histidinyl axial iron coordination and low redox potentials. We have purified two new cytochromes c with markedly different molecular masses (10 000 and 50 000) from the bacterium Desulfuromonas acetoxidans, which uses anaerobic sulfur respiration as its sole energy source. The characterization by electrochemistry and optical and EPR spectroscopies revealed the cytochrome c (Mr = 10 000) to be the first monohemic cytochrome c exhibiting a bis-histidinyl axial coordination and a low redox potential (-220 mV). The cytochrome c (Mr = 50 000) contains four hemes of low potential (-200, -210, -370, and -380 mV) with the same axial coordination. The N-terminal amino acid sequences were compared with that of the trihemic cytochrome c7, previously described in D. acetoxidans and which is related to tetrahemic cytochrome c3 from sulfate reducing bacteria. Some homology was found between cytochrome c (Mr = 10 000) and cytochrome c7. Both D. acetoxidans cytochromes c are located in the periplasmic space and their biochemical and spectroscopic properties indicate that they belong to the class III cytochromes.

Two young Somalians with gastric outlet obstruction as a first manifestation of gastroduodenal tuberculosis.

Gastroduodenal tuberculosis (GDTB) is an uncommon condition which can mimic other gastrointestinal disorders. It usually occurs secondary to pulmonary tuberculosis. We describe two young Somalian patients who presented with abdominal pain and gastric outlet obstruction. GDTB was diagnosed in both patients and they were successfully treated with antituberculous drugs.

High plasma antithrombin levels in acute hepatitis A.

BACKGROUND: Laboratory testing of antithrombin serves to demonstrate a decreased concentration that is indicative of a thrombotic tendency. We report unexpected high levels of antithrombin in a patient with hepatitis A. METHODS: A 37-year-old woman with a 4-week history of acute hepatitis A was studied. The diagnosis of cholestatic hepatitis A was confirmed by positive serology and liver biopsy. The patient recovered completely within 6 months. RESULTS: Antithrombin activity was increased (234%; reference range, 80-120%). This high activity was confirmed by an antithrombin antigen of 210%. On recovery antithrombin activity returned to normal. CONCLUSIONS: We are unaware of other reports of such high levels of antithrombin, in particular in patients with hepatitis A. It is not clear whether the high concentration observed in this case is due to an acute-phase reaction or to impaired clearance by the liver. The presence of a molecular variant with different secretion characteristics is unlikely, since antithrombin activity returned to normal on recovery, suggesting base-line values within the normal range.

Hepatocholedochal cysts. A rare cause of obstructive jaundice.

The case history is described of a 21-year-old woman who, after analysis because of jaundice and pain in the upper abdomen, was diagnosed as having hepatocholedochal cysts Type IV-A. Surgery was performed. In connection with this case history the literature on hepatocholedochal cysts is reviewed.

Amino-acid sequence of cytochrome c-553 from Desulfovibrio desulfuricans Norway.

The amino-acid sequence of the cytochrome c-553 from Desulfovibrio desulfuricans Norway has been determined and compared with that of two different cytochromes c-553 from D. vulgaris already described and with that cytochrome c-551 from Pseudomonas. This low-molecular-weight monohemic cytochrome comprises 80 amino acids and has the typical characteristics of small cytochromes such as mitochondrial cytochromes. Secondary-structure predictions are deduced from sequence data and are compared with X-ray three-dimensional structures of low-molecular-weight cytochrome c. The phylogenetic situation of Desulfovibrio cytochromes c-533 in the cytochrome c superfamily is discussed.

Amino-acid sequence of rusticyanin from Thiobacillus ferrooxidans and its comparison with other blue copper proteins.

Rusticyanin, a copper protein characterized by a high redox potential (+680 mV) and a high stability at acidic pH, is involved in iron oxidation in Thiobacillus ferrooxidans. It has been characterized from a new strain and its amino-acid sequence has been determined and compared to two other rusticyanin sequences isolated from different strains. It comprises 155 amino acids and the alignment of the three rusticyanins shows a high degree of homology. Comparing the rusticyanins with six blue copper proteins which have a copper-I site in common, a consensus sequence containing Cys, His and Met in the C-terminal part of the protein and His-85 is proposed to be involved in the copper coordination. Secondary structure predictions are compared to three structures of copper proteins obtained by X-ray crystallography.

Characterization in rat pancreatic juice of a protein homologous to the human pancreatic stone protein.

1. The pancreatic stone protein (PSP, Mr 15,000) which has been discovered in human calculi derives from the native glycosylated forms of the protein (Mrs 17,500-22,000) which are present in human pancreatic juice through tryptic cleavage of the Arg 11-Ile 12 bond. 2. In the present study, a homologous native form of the protein (Mr 17,000) was purified from rat pancreatic juice. 3. Its N-terminal amino acid sequence was found to display a high degree of homology with that of the human native protein forms, apart from the fact that it was not glycosylated. 4. In rat as in human, tryptic cleavage of the Arg 11-Ile 12 bond transforms a soluble protein into one which is practically insoluble at neutral pH.

Electrostatic effects and the dynamics of enzyme reactions at the surface of plant cells. 3. Interplay between limited cell-wall autolysis, pectin methyl esterase activity and electrostatic effects in soybean cell walls.

Soybean cell walls display a process of autolysis which results in the release of reducing sugars from the walls. Loosening and autolysis of cell wall are involved in the cell-wall growth process, for autolysis is maximum during both cell extension and cell-wall synthesis. Autolysis goes to completion within about 50 h and is an enzymatic process that results from the activity of cell wall exo- and endo-glycosyltransferases. The optimum pH of autolysis is about 5. Increasing the ionic strength of the bulk phase where cell-wall fragments are suspended, results in a shift of the pH profile towards low pH. This is consistent with the view that at 'low' ionic strength, the local pH in the cell wall is lower than in the bulk phase. One of the main ideas of the model proposed in a preceding paper, is that pectin methyl esterase reaction, by building up a high fixed charge density, results in proton attraction in the wall. Low pH must then activate the wall loosening enzymes involved in autolysis and cell growth. This view may be directly confirmed experimentally. The pH of a cell-wall suspension, initially equal to 5, was brought to 8 for 20 min, then back to 5. Under these conditions, the rate of cell-wall autolysis was enhanced with respect to the rate of autolysis obtained with cell-wall fragments kept at pH 5. The pH response of the multienzyme plant cell-wall system basically relies on opposite pH sensitivities of the two types of enzymes involved in the growth process. Pectin methyl esterase, which generates the cell-wall Donnan potential, is inhibited by protons, whereas the wall-loosening enzymes involved in cell growth are activated by protons.