Since reactive ammonia is not available under physiological conditions, glutamine is used as a source for the incorporation of nitrogen in a number of metabolic pathway intermediates. The heterodimeric ImGP synthase that links histidine and purine biosynthesis belongs to the family of glutamine amidotransferases in which the glutaminase activity is coupled with a subsequent synthase activity specific for each member of the enzyme family. Its X-ray structure from the hyperthermophile Thermotoga maritima shows that the glutaminase subunit is associated with the N-terminal face of the (beta alpha)(8) barrel cyclase subunit. The complex reveals a putative tunnel for the transfer of ammonia over a distance of 25 A. Although ammonia tunneling has been reported for glutamine amidotransferases, the ImGP synthase has evolved a novel mechanism, which extends the known functional properties of the versatile (beta alpha)(8) barrel fold.

Two novel angucyclinone-type antibiotics, simocyclinones D4 and D8, were detected in the mycelium extract of Streptomyces antibioticus Tii 6040 by HFLC-diode-array and HPLCelectrospray-mass-spectrometry screening. The compoundsshowantibiotic activities against Gram-positive bacteria and cytostatic effects on various tumor cell lines.

An unusual type I polyketide defined in a unique hexacyclic skeleton was determined as the structure of hexacyclinic acid (1). The structure was elucidated by X‐ray analysis in connection with chemical–spectroscopic methods, and the biosynthesis was explored through feeding experiments with 13C‐labeled precursors. The compound was isolated by application of the OSMAC approach to Streptomyces cellulosae S 1013.

Variation of the culture conditions − static surface cultures in particular − of the fungus Sphaeropsidales sp. (strain F-24Ј707), which produces cladospirone bisepoxide (1), led to the isolation of eight new spirobisnaphthalenes − the cladospirones B to I (8−15) − together with seven known representatives of this class of secondary metabolites. Cladospirones C (9) and D (11) show antibiotic activity against bacteria and algae. The structures of cladospirone B (8) and E (12) were confirmed by X-ray structure analysis. Cladospirones C (9)[ ‡] Part 41: Ref. [1] [a]

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