| Summary: | This study has been based on a working hypothesis which proposes that the bactericidal action of ultraviolet light is attributable to an absorption of energy in the ultraviolet region by one or more essential cellular metabolites. It is further suggested that the absorption produces a molecular shift in the absorbing metabolite (in this case p-aminobenzoic acid) of such a nature that the altered compound, while structurally still quite similar to its metabolic precursor, is sufficiently different to interfere with the normal metabolic functions of the cell. Bacteriostasis then follows and ultimately death ensues.
The literature associated with the biological action of ultraviolet light and the study of p-aminobenzoic acid and sulphonamides as well as other related subjects gives circumstantial evidence to support the above hypothesis has been reviewed and is presented by sections in the thesis.
The establishment of a microbiological assay procedure for the determination of p-aminobenzoic acid was done in order to detect if ultraviolet radiation is able to produce an alteration in the p-aminobenzoic acid molecule.
A microbiological assay procedure for the determination of p-aminobenzoic acid has been recommended, as it was found necessary to modify the published assay procedures.
It was suggested that this recommendation should be followed in future work along the lines of the experimentations reported herein.
In the study of the biological action of ultraviolet irradiation it seems safe to conclude that the hypothesis upon which the present work is based is sound, at least, in part, in that it has been demonstrated that irradiation of p-aminobenzoic acid so alters the compound that it can no longer act as an "essential metabolite" for Acetobacter suboxydans, under the prevailing conditions.
Experimentations were carried out to show the effect of ultraviolet irradiation on the cells of Acetobacter suboxvdans, and the subsequent study to observe if the "essential metabolite", p-aminobenzoic acid, was able to counteract the actions of these irradiations.
A study of the chemical action of ultraviolet light on p-aminobenzoic acid was included. Determination of the absorption curves of normal and irradiated p-aminobenzoic acid were carried out with the aid of the Beckman Model DU Spectrophotometer. It was shown that the absorption curve of irradiated p-aminobenzoic acid differed markedly from that of normal p-aminobenzoic acid. Preliminary attempts to isolate the irradiation product or products of p-aminobenzoic acid were made. Various solubility tests of the new compound were carried out and recorded. It is impossible at present to state the identity of the irradiation product of p-aminobenzoic acid; however future work which is planned may be successful in isolating the compound or compounds in a pure state and with this result the identity of these compounds may be established.
The original hypothesis emphasized the likelihood that the irradiation product of p-aminobenzoic acid would act as an anti-metabolite. The work reported, does not support such a contention in entirety. It does suggest that either an anti-metabolite is formed or more likely that the "essential metabolite", p-aminobenzoic acid, is destroyed by irradiation as determinable by microbiological assay. === Land and Food Systems, Faculty of === Graduate
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