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Effect of Excess Dietary Methionine on the Catabolism of Cysteine in Rats¹

Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853

The effect of excess methionine (MET) on cysteine (CYS) catabolism was investigated in rats prefed either a control (10% casein + 0.3% L-MET) or high-MET (10% casein + 3.0% L-MET) diet for 5 or 20 days. The activities of cysteine dioxygenase, cysteine desulfhydrase and cystathionase were increased in high-MET rats to levels 5.9, 2.7 and 2.7 times, respectively, those of control rats after 5 days and to 2.9, 20 and 2.7 times control levels after 20 days. Cysteine aminotransferase and cystathionine synthase activities were increased to 1.5 and 1.7 times control values after 5 days but were not significantly different from control values at 20 days. Following gastric intubation of 5 g of an L-amino acid diet containing 0.2% L-[³⁵S]CYS, the 24-hour urinary excretion of ³⁵SO₄, [³⁵S]taurine and total ³⁵S (% of administered dose) and the [³⁵S]taurine: ³⁵S and [³⁵S]taurine:³⁵SO₄ ratios were increased in rats prefed excess MET for 5 or 20 days. When 2.6% L-[³⁵S]CYS was administered similarly, no significant differences between high-MET and control rats were observed. However, the [³⁵S]taurine:³⁵S and [³⁵S]taurine: ³⁵SO₄ ratios were elevated in both high-MET and control rats given 2.6% L-[³⁵S]CYS over those for control rats fed 0.2% L-[³⁵S]CYS. The increase in cysteine dioxygenase activity and the increase in [³⁵S]taurine:³⁵SO₄ ratio in rats fed excess MET or given a load dose of CYS suggest that the cysteine sulfinic acid pathway plays a major role in the regulation of CYS degradation.

KEY WORDS: • cysteine • methionine • sulfate • taurine • cysteine dioxygenase

¹ This research was supported in part by funds made available through the State University of New York and in part by New York State Hatch Funds.

Manuscript received 12 April 1979.

This article has been cited by other articles:

				M. H. Stipanuk, J. E. Dominy Jr., J.-I. Lee, and R. M. Coloso Mammalian Cysteine Metabolism: New Insights into Regulation of Cysteine Metabolism J. Nutr., June 1, 2006; 136(6): 1652S - 1659S. [Abstract] [Full Text] [PDF]