Antibiotics, biosynthesis constituents

Different lines, each with Insect resistance, may possess different ratios of antibiotic compounds. Thus, It may be possible to Increase resistance by crossing lines where each contributes genes for biosynthesis of different antibiotic compounds. The tobacco budworm was selected for study In preference to the cotton bollworm because It Is easier to rear and use In the laboratory, Is more resistant to Insecticides In the field, and It Is approximately as susceptible to cotton constituents Incorporated In laboratory diets (14). This present study was carried out to Identify and analyze for cotton constituents that were toxic In laboratory feeding tests, and to determine whether there were positive correlations of their content In leaves and/or other tissue with field resistance. From this Information, the generation of lines with multiple factors for resistance could be Initiated. 

A large number of a, 3-didehydro-a-amino acids have been identified as constituents of relatively low molecular weight cyclic compounds from microbial sources. However, the presence of a,p-didehydroalanine in bacterial as well as in mammalian histidine ammonia lyase and in phenylalanine ammonia lyase shows that the occurrence of a,p-didehydro-a-amino acids is not limited to small molecules alone 8 These residues are incorporated in natural sequences by posttranslation modification. a,p-Didehydro-a-amino acids have also been postulated to be precursors in the biosynthesis of several heterocyclic metabolites including penicillin and cephalosporin 9 Other well-known compounds containing ,( -di-dehydro-a-amino acids are nisin 10,11 (a food preservative112 ), subtilin (a broad spectrum antibiotic) 13 and some of the metabolites isolated from Streptomyces strains such as gri-seoviridin 14 ... 

Biosynthesis of (S)-/ -Tyrosine in Bacillus brevis Vm4 //-Tyrosine 43 is a constituent of the peptide antibiotics edeine A and B [60] obtained from cultures of BaciUus brevis Vm4. //-Tyrosine is derived from a-tyrosine 42 by use of a tyrosine 2,3-aminomutase [61]. The purified enzyme has properties fundamentally different from those of all other aminomutases so far mentioned. It requires ATP and Mg2+ ions, but no other cofactors. 

As a model system we would like to describe the biosynthesis of bacitracin, a commercially important peptide antibiotic. Its mechanism of formation has been studied in our laboratory as well as by others. A cell free system for bacitracin production by B. Hcheniformis ATCC 10716 was reported by Ishihara et al.(29). The methods used were modified (Ref. 31) and a partially purified enzyme complex which performed de novo synthesis of bacitracin from the L-isomers of the constituent amino acids, ATP and Mg2 was isolated (Ref. 31 - 34). D-glutamic acid and D-phenylala-nine which occur in bacitracin support its synthesis (Ref. 31). This was also the case for D-aspartic acid (unpublished results). 

A generalized biosynthetic the tics envisages that the formation of involves the insertion of amino acid e.g., diketopiperazines and postulat D-amino acid constituents takes plac after their incorporation into stere mediates.There seems to be gene biosynthesis of peptide antibiotics, a purely enzymatic process and does RKA participation required in protei... 

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