[Antral vascular ectasia--"water-melon stomach". An overlooked cause of iron deficiency anemia?]. / Antral vaskulaer ektasi--"vandmelon-mavesaekken". En overset årsag til blødningsanoemi?

Antral vascular ectasia or "the watermelon stomach" (WS) is an endoscopically, histologically and clinically distinct entity. The term WS reflects the endoscopic appearance of longitudinal antral erythematous folds containing visible vessels radiating from the pylorus. Histological examination demonstrates characteristic features including dilated mucosal capillaries, focal thrombosis and fibromuscular hypertrophy of the lamina propria. The clinical picture is characterized by severe chronic iron deficiency anaemia, and failure to recognize WS has frequently delayed adequate treatment for several years. Antrectomy is a definitive cure. Both endoscopic laser- and sclerotherapy seem to be promising alternative methods in the treatment of WS.

[Acute uremia after renal cholesterol embolism]. / Akut uraemi efter renale kolesterolembolier.

A case of acute uraemia caused by cholesterol emboli in the kidneys in a sixty-six year old male with arteriosclerosis is presented. No effective treatment is available, but recognizing the condition may save the patient from otherwise time-consuming extensive diagnostic programmes.

Substrate specificity of aspartate transcarbamylase. Interaction of the enzyme with analogs of aspartate and succinate.

The ability of aspartate transcarbamylase from Escherichia coli to catalyze carbamylation of amino acids other than the natural substrate, L-aspartate, was examined. Cysteine, cysteate, cysteinesulfinate, and 3-nitroalanine showed kcat values at pH 7 of 0.16, 0.58, 5.2, and 62 s-1, respectively, while kcat with aspartate was 320 s-1. In a parallel study, competitive inhibition constants of 3-nitropropionate, 3-mercaptopropionate, 3-sulfopropionate, and 3-sulfinopropionate were found to be high, about 0.1 M, compared with that of succinate, 0.56 mM. Although cysteinesulfinate had low activity as a substrate, the pH dependences of kcat and kcat/Km in H2O and D2O observed with the compound closely paralleled those of aspartate. The results of these studies suggest that substrate specificity and reactivity are achieved in part by a strong, highly specific interaction of one or more active site residues with the beta-carboxylate of L-aspartate. Unlike the sigmoidal kinetics found with aspartate, saturation of native aspartate transcarbamylase by cysteine sulfinate showed a lack of cooperativity, even under conditions of activation of the reaction by ATP and inhibition by CTP. The cysteinesulfinate reaction was increased 9-fold by the bisubstrate analog N-phosphonacetyl-L-aspartate. These results were interpreted in terms of an inability of cysteinesulfinate to cause the allosteric conformational change promoted by aspartate.

Metal cation influence on activity and regulation of aspartate carbamoyltransferase.

At saturating carbamoylphosphate and nonsaturating aspartate concentrations, Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Al3+, and Gd3+ inhibit aspartate carbamoyltransferase (carbamoylphosphate:L-asparate carbamoyltransferase, EC 2.1.3.2) from EScherichia coli. When nucleotide triphosphates are present, these inhibitory effects are displaced to higher concentrations of cation. At lower levels of cation and saturating carbamoylphosphate concentration, Mg2+, Mn2+, Al3+, and Gd3+ partially relieve allosteric inhibition by GTP but have little influence on activation by ATP and inhibition by CTP. At nonsaturating carbamoylphosphate concentrations, however, Mg2+, Mn2+, Al3+, and Gd3+ increase enzymatic activity to 170% over the level when GTP alone is present. In addition, Mg2+, Mn2+, and Al3+ show enhancement of ATP activation by 120-130% but only slight relief of CTP inhibition. We suggest that three modes of action by the metal can account for the observed kinetic behavior. (i) In the absence of nucleotide, metals inhibit catalytic activity either by a direct interaction with the enzyme or indirectly by complexing carbamoylphosphate. (ii) The metal-nucleotide complex interacts allosterically with the enzyme to enhance enzymatic activity relative to that produced by the free nucleotide, as noted above. (iii) By chelating to nucleotides, the metal diminishes their tendency to bind competitively at the carbamoylphosphate portion of the active site, as shown particularly by experiments on the catalytic subunit.