Masters Theses
Date of Award
3-1966
Degree Type
Thesis
Degree Name
Master of Science
Major
Nutrition
Major Professor
Jane R. Savage
Committee Members
Mary Nelle Traylor, Claire Gilbert
Abstract
(From the Introduction): The quest for the cause of pellagra which started in the early eighteenth century is surrounded with many fascinating theories. According to Harris (1)*, the many early theories advanced for the causation of pellagra may be classified into four groups: toxins, infections, food deficiencies of quantity and quality, and vitamin deficiencies. Maize consumption was associated with pellagra as early as 1735 by Casal but its relationship to the disease was not exactly understood at that time.
The first unreserved claim that pellagra results solely from the use of corn in the diet was made by Franzoni in 1807. Pellagra was defined as "a food poisoning generally due to the use of spoiled corn, having the characteristics of endemicity in the countries where spoiled corn is consumed as food, and seasons in which the corn crop is most seriously damaged" (2).
Goldberger et al. (3) in 1916 made the observation that the diet of pellagrous patients was unbalanced, being low in protein. Later work in 1924 showed that zein, the major protein in corn, was low in tryptophan. When it was finally established that pellagra was caused by a deficiency of niacin and its precursor tryptophan, a possible explanation offered for the association between diets high in corn and pellagra was the low tryptophan content in zein.
In 1945 Krehl et al. (4) made the observation that the addition of tryptophan-deficient proteins, such as gelatin and zein, to low-protein niacin-free diets resulted in the retardation of growth and the development of niacin-deficiency symptoms in rats. These symptoms were alleviated by the addition of tryptophan or niacin to the diets. The inhibition of growth which resulted from the inclusion of corn in the ration used by Krehl and his associates and the apparent dual role of niacin and tryptophan in counteracting this growth depression have resulted in considerable study on the mechanism of these relationships.
In a study by Goldsmith et al. (5) human subjects fed corn diets developed clinical signs of a niacin deficiency within 50 days, whereas subjects fed a wheat diet containing the same amounts of niacin and tryptophan as the corn diet did not show any niacin deficiency symptoms until they had been on the diet for 80 days or more. These studies suggested that some component of corn interferes with the utilization of tryptophan and/or niacin. It was theorized that the development of niacin-deficiency symptoms resulting from ingestion of corn diets might be due to an amino acid imbalance.
The ability of the rat to convert tryptophan to niacin has made it difficult to resolve the question of whether the substances causing such imbalances affect tryptophan utilization, or niacin utilization or the pathway in the conversion of niacin from tryptophan.
In 1964 Coulter (6) studied the utilization of tryptophan for pyridine nucleotide synthesis in rats fed low-protein niacin-free diets containing either corn, zein, mixtures of the indispensable amino acids as found in zein with and without leucine, or a mixture of the dispensable amino acids as found in zein. The pyridine nucleotides are the metabolically-active form of niacin in the body. She found that zein, leucine, and one or more of the dispensable amino acids of zein interfered with the ability of the rat to synthesize pyridine nucleotides from tryptophan.
In 1965 Ellis (7) studied the effect of the stepwise addition of the dispensable amino acids of zein on the utilization of L-tryptophan for pyridine nucleotide synthesis in rats fed low-protein niacin-free diets. Her findings indicated that glutamic acid and possibly tyrosine inhibited the utilization of tryptophan.
The occurrence of certain intermediate products of tryptophan metabolism in the urine of mammals has provided important clues toward unraveling the metabolic pathway for the conversion of tryptophan to niacin. From the cumulative evidence obtained in studies with different organisms it appears that the initial steps in the major pathway of tryptophan metabolism are: tryptophan→ formylkynurenine → kynurenine → 3-hydroxykynurenine→ 3-hydroxyanthranilic acid (8). Recent studies have shown that 3-hydroxyanthranilic acid is further metabolized to niacin ribonucleotide (9). Many of the metabolites along the tryptophan-niacin pathway have been detected in urine of rats and humans. Estimation of the quantities of these metabolites in the urine under various experimental conditions has been helpful in assessing the metabolic use of tryptophan and in diagnosing certain diseases.
In view of these considerations, this study was designed to determine the effect of zein, leucine, and glutamic acid on the urinary excretion of kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid in the rat. An interference in any of the steps in the pathway of tryptophan metabolism (indicated above) would be expected to cause an increase in the urinary excretion of the specific metabolite formed in the preceding step. For example, an interference in the conversion of 3-hydroxykynurenine to 3-hydroxyanthranilic acid would be expected to cause an increase in the urinary excretion of 3-hydroxykynurenine.
Recommended Citation
Acacio, Florecita B., "The Effect of Zein, Leucine, and Glutamic Acid on the Urinary Excretion of Kynurenine, 3-Hydroxykynurenine, and 3-Hydroxyanthranilic Acid in the Rat. " Master's Thesis, University of Tennessee, 1966.
https://trace.tennessee.edu/utk_gradthes/3938