Studies on terpenes

The problem of bacterial diarrhoea

The reported incidence of "pathogenic" bacteria, as judged by serotype, in the stools of children with acute diarrhoea has varied from 4 to 33% over the last twenty years. Techniques such as tissue culture provide a means for detecting enterotoxin-producing strains of bacteria, strains which often do not possess "pathogenic" serotypes. "Pathogenicity" requires redefinition, and the aetiological importance of bacteria in diarrhoea is probably considerably greater than previous reports have indicated. Colonization of the bowel by a pathogen will result in structural and/or mucosal abnormalities, and will depend on a series of complex interactions between the external environment, the pathogen, and the host and its resident bacterial flora. Enteropathogenic bacteria may be broadly classified as (i) invasive (e.g. Shigella, Salmonella and some Escherichia coli) which predominantly affect the distal bowel, or (ii) non-invasive (e.g. Vibrio cholerae and E. coli) which affect the proximal bowel. V. cholerae and E. coli elaborate heat-labile enterotoxins which activate adenylate cyclase and induce small intestinal secretion; the secretory effects of heat-stable E. coli and heat-labile Shigella dysenteriae enterotoxins are not accompanied by cyclase activation. The two major complications of acute diarrhoea are (i) hypernatraemic dehydration with its attendant neurological, renal and vascular lesions, and (ii) protracted diarrhoea which may lead to severe malnutrition. Deconjugation of bile salts and colonization of the small bowel with toxigenic strains of E. coli may be important in the pathophysiology of the protracted diarrhoea syndrome. The control of bacterial diarrhoea requires a corrdinated political, educational, social, public health and scientific attack. Bacterial diarrhoea is a major health problem throughout the world, and carries an appreciable morbidity and mortality. This is particularly the case during infancy, and in those developing parts of the world where malnutrition is common. This paper is concerned mainly with acute bacterial diarrhoea, and reviews the problem as a whole.

Monoterpene cyclases: use of the noncyclizable substrate analog 6,7-dihydrogeranyl pyrophosphate to uncouple the isomerization step of the coupled isomerization-cyclization reaction

Enzymes from Salvia officinalis capable of catalyzing the isomerization and subsequent cyclization of geranyl pyrophosphate to the monoterpenes (+)-alpha-pinene and (+)-bornyl pyrophosphate were examined with the noncyclizable substrate analog 6,7-dihydrogeranyl pyrophosphate in an attempt to dissect the cryptic isomerization step from the normally coupled reaction sequence. The analog inhibited the cyclization of geranyl pyrophosphate and was itself catalytically active, affording acyclic terpene olefins and alcohols as products. The enzymatic products generated from 6,7-dihydrogeranyl pyrophosphate qualitatively resembled the solvolysis products of 6,7-dihydrolinalyl pyrophosphate, yet they constituted a far higher proportion of olefins, suggesting that enzymatic product formation occurs in an environment relatively inaccessible to water. Since the normal cyclization of geranyl pyrophosphate is considered to proceed via preliminary isomerization to the bound tertiary intermediate (3R)-linalyl pyrophosphate, the results suggest that the analog undergoes the normal pyrophosphate ionization-migration step, giving rise in this case to (3R)-6,7-dihydrolinalyl pyrophosphate which is reionized, and because the subsequent cyclizations are precluded, the resulting cation is either deprotonated or captured by water. In divalent metal ion requirement, pH optimum, and other characteristics, the enzymatic transformation of the analog resembles the normal monoterpene cyclase reaction.