The tricarboxylic acid cycle of Helicobacter pylori

The composition and properties of the tricarboxylic acid cycle of the micro aerophilic human pathogen Helicobacter pylori were investigated in situ and in cell extracts using [H-1] and [C-13]-NMR spectroscopy and spectrophotom etry. NR LR spectroscopy assays enabled highly specific measurements of som e enzyme activities, previously not possible using spectrophotometry, in in situ studies with PI. pylori, thus providing the first accurate picture of the complete tricarboxylic acid cycle of the bacterium. The presence, cell ular location and kinetic parameters of citrate synthase, aconitase, isocit rate dehydrogenase, alpha-ketoglutarate oxidase, fumarate reductase, fumara se, malate dehydrogenase. and malate synthase activities in H. pylori are d escribed. The absence of other enzyme activities of the cycle including alp ha-ketoglutarate dehydrogmase, succinyl-CoA synthetase, and succinate dehyd rogenase also are shown. The H. pylori tricarboxylic acid cycle appears to be a noncyclic, branched pathway, characteristic of anaerobic metabolism, d irected towards the production of succinnte in the reductive dicarboxylic a cid branch and alpha-ketoglutarate in the oxidative tricarboxylic acid bran ch. Both branches were metabolically linked by the presence of or-ketogluta rate oxidase activity. Under the growth conditions employed, H. pylori did not possess an operational glyoxylate bypass, owing to the absence of isoci trate lyase activity: nor a gamma-aminobutyrate shunt, swing to the absence of both gamma-aminobutyrate transaminase and succinic semialdehyde dehydro genase activities. The catalytic and regulatory properties of the H. pylori tricarboxylic acid cycle enzymes are discussed by comparing their amino ac id sequences with those of other, more extensively studied enzymes.