QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Everett, G. B. Articles by Benevenga, N. J. Search for Related Content PubMed PubMed Citation Articles by Everett, G. B. Articles by Benevenga, N. J.

Methionine Transamination and Catabolism in Vitamin B-6 Deficient Rats¹

Departments of Nutritional Sciences and Meat and Animal Science, University of Wisconsin, Madison, Wisconsin 53706

Methionine (Met) transamination and oxidation of the Met or -keto--methiolbutyrate (KMB) carboxyl and methyl carbons were studied in weanling rats fed control or vitamin B₆ deficient diets containing 18 or 60% casein for a period of 21 days. In homogenates prepared from the livers of B₆ deficient rats, transamination of Met was reduced to 8 to 16% of controls. Transamination was partially restored by addition of pyridoxal phosphate (PALP) to the homogenates. Vitamin B₆ deficiency resulted in a 61 to 76% reduction in oxidation of the Met carboxyl carbon which was also partially restored by the addition or PALP. The high protein diet stimulated transamination of Met and oxidation of the carboxyl carbons of both Met and KMB. Oxidation of the methyl carbon was relatively unaffected by either B₆ deficiency or high protein diet. In vivo, the oxidation of the Met carboxyl carbon was not influenced by either B₆ deficiency or high protein diet, however, oxidation of the methyl carbon increased 32 to 53% in rats fed the B₆ deficient diets. It appears that transamination was not rate limiting in vivo, even with a B₆ deficiency, however, in vitro with greater substrate loading transamination may become rate limiting for oxidation of the carboxyl carbon of Met. In vivo the B₆ deficiency may have resulted in a shift of Met metabolism from the transsulfuration pathway, which conserves the methyl carbon and partially conserves the carboxyl carbon depending on the fraction of homocysteine remethylated, to the transaminative pathway which results in extensive oxidation of both carbons.

KEY WORDS: • methionine • transamination • pyridoxine • -keto--methiolbutyrate • rat

¹ This research was supported by funds from the College of Agricultural and Life Sciences, University of Wisconsin and by U.S. Public Health Service Research Grant AM 15227.

² Present address: Department of Physiological Chemistry, University of California, School of Veterinary Medicine, Davis, California 95616.

³ Present address: Department of Pathology, Medical School, University of Wisconsin, Madison, Wisconsin 53706.

Manuscript received 25 November 1978.