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Studies on the structure of the phytopathogenic toxin of Pseudomonas tabaci.

D. Woolley,G. Schaffner,A. C. Braun

Published 1955 in Journal of Biological Chemistry

ABSTRACT

A pathogenic factor in wildfire disease of tobacco, the toxin of Pseudomonas tabaci, which has been shown to be an antagonist of methionine (l), has recently been isolated in pure form (2). A major constituent of this toxin has been identified as the new amino acid tabtoxinine, or cy , e-diamino,&hydroxypimelic acid (3). The object of the present study was to determine the entire structure of the toxin. The results indicated that the structure is that shown in Fig. 1. The following kinds of evidence led to the proposal of this formula: (a) Elementary analysis of the toxin gave values which would correspond to %1&-06Nz. Because no satisfactory method for the determination of molecular weight could be applied, this empirical formula was the minimal one possible. There was some doubt about the reliability of the analytical figures because of the inauspicious properties of the isolated toxin (2). (b) After hydrolysis, at least 55 per cent of the dry weight of the toxin could be isolated as tabtoxinine (3). Clearly, then, this amino acid represented a major part of the toxin. (c) One-half of the total nitrogen of the toxin was a-amino nitrogen (2). This suggested that one of the amino groups of tabtoxinine was free and the other was combined. Acid hydrolysis rendered almost all of the nitrogen in a form determinable as a-amino nitrogen. (d) The products of complete hydrolysis with acid were isolated and found to be tabtoxinine and lactic acid. Small amounts of formic acid were also identified, but these were considered to have arisen from decomposition of the major components. Diligent search failed to reveal any other constituent. For example, no evidence for a volatile alcohol was found in the methoxyl determination. Similarly, no other acidic components could be detected. (e) Different hydrolytic procedures gave two different ninhydrinpositive substances. The one produced by strong acid was tabtoxinine. The other was formed when the toxin was inactivated by very weak alkali (2). This latter substance, called the alkali-inactivated toxin, was converted to tabtoxinine by either strong acid or strong alkali. It was thus a product of partial cleavage (see Fig. 1).

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