Document Type

Dissertation - Open Access

Award Date

1973

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry

First Advisor

Oscar E. Olson

Abstract

The primary structure of the antifungal peptide nifungin was studied. Amino acid analysis of nifungin before and after performic acid oxidation revealed 51 amino acids and the presence of an unidentified ninhydrin positive material. The unidentified material constituted approximately ten per cent of nifungin by weight. It contains nitrogen but, as reported by others (2), did not contain phosphate or reducing sugars. It was not hydrolyzed into smaller compounds by strong mineral acids. Carboxyl terminal analysis was conducted utilizing carboxy-peptidase A and B on both the oxidized and unoxidized nifungin. Tyrosine appeared to be released most rapidly followed by lysine, however, the results were not conclusive and the interpretation must await further studies. Comparing the elution of nifungin from a column of sephadex to the elution from the same column of proteins having known molecular weights showed that the nifungin molecule is a monomer containing the 51 amino acid residues and the unknown compound. Based upon the moles of amino acids recovered from a known amount of nifungin a molecular weight of 6810 was determined for unoxidized nifungin. Oxidized nifungin was digested with trypsin and the resulting peptides separated using Aminex AG 50W X 2 resin. The complete amino acid sequence of six tryptic peptides and partial sequence of five other peptides was determined. Combination of peptides indicated the sequence of CySO3H-Tyr-Val-Lys-Thr- CySO3H-Ala-Ile-Lys-(Lys, CySO3H, CySO3H) and Asp-Asn- CySO3H-Ile-Lys-Lys accounting for 18 of the 51 amino acids found in nifungin. The nifungin molecule appeared to be quite complex as revealed by the presence of numerous 1/2 cystine residues, no free sulfhydryl groups and high resistance to carboxypeptidase enzymes.

Library of Congress Subject Headings

Amino acids
Peptides

Format

application/pdf

Publisher

South Dakota State University

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Included in

Chemistry Commons

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