Cyclic polypeptide complex antibiotic

Capreomycin is a cyclic polypeptide complex antibiotic having a structure very much similar to viomycin, and produced by Streptomyces capreolus as a mixture of about four different components. It exerts its bacteriostatie aetion against certain mycobacterial strains, such as M. tuberculosis M. bovis M. kansasii, andM. avium by an unknown mechanism of action. However, its pharmacological and antibacterial activities are quite akin to the aminoglycosides. 

Albomycin an antibiotic synthesized by Actinomyces subtropicus. A. is a cyclic polypeptide containing a pyrimidine base (cytosine) and 4.16% Fe in the form of a hydroxamate-Fe(IIl) complex (Fig.). It is one of the sideromycins (similar to, and possibly identical to, grisein), and it interferes with iron metabolism as an antimetabolite of the sideramines. A. is effective against both Gram-positive and Gram-negative bacteria, and inhibits the aerobic metabolism of Staphylococcus aureus and E. colt... 

The study of the conformational behavior of polypeptides has intrinsic interest in a complex and challenging theoretical and experimental problem. There are also strong biological implications inasmuch as there are many known naturally occurring polypeptides, both linear and cyclic, with potent effects as hormones, toxins, antibiotics, and ionophores. It is very probable that these functions are closely related to the polymer chain conformations. Investigations of model polypepetides have been extremely useful for the interpretation of conformational behavior and for the elucidation of the interaction between proteins and other macromolecules. The conformational structures of polyproline and related compounds have been of particular interest due to the important role L-proline plays in effecting protein structure. 

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