The host-specific toxin of Helminthosporium carbonum (C32HsoNoO,o) was hydrolyzed by 6 N HCI to yield a number of a-amino acids. The common amino acids, proline and alanine, occurred in a ratio of 1 :2. Two other unstable a-amino acids that produced lower color values with ninhydrin were also produced. One of these was tentatively identified as 2-amino-2,3-dehydro-3-methylpentanoic acid by electrolytic reduction to isoleucine. Additional ninhydrin-reacting substances were produced in low yield and probably represented secondary hydrolysis products of the unstable amino acids. (4,5,8,9,16,17 The most recent studies have been concerned with the hostspecific toxin of Helminthosporium carbonum Ullstrup, which is toxic to susceptible inbred dent corn (Zea inays L.) (3,6,7,14,15,19).Although each of these host-specific toxins has been isolated and crystallized in milligram quantities, because of the difficulty of isolation and their great instability only HC2 toxin has been characterized to any extent (5, 6, 7). It was shown to have a molecular formula approximating C32H.NMO,O by analysis of crystalline material and by analysis of a crystalline hydrochloride derivative. The molecular weight was determined by bioassay of the eluate of a Sephadex G-10 chromatography column and shown to be slightly less than 700. The toxin appeared to be a cyclic peptide, because, although it did not react with ninhydrin or fluorodinitrobenzene, after acid hydrolysis it yielded compounds which reacted to these reagents. The ultraviolet absorption spectrum of freshly lyophilized toxin dissolved in freshly distilled ethanol showed a single, well defined maximum at 230 nm. The molar absorptivity of a 1.4 X 10' M solution (assuming a molecular weight of 679) was approximately 5000. The position of the maximum and its relatively high intensity suggested a double bond in the vicinity of a carbonyl group, possibly an a , fl-unsaturated amide. Because the presence of such a function in HC toxin would explain the relative instability of the molecule, further work was done in characterizing the ninhydrin-reacting products of acid hydrolysis.
MATERIAL AND METHODS