It has been shown that washed disks of turnip storage tissue accumulate S-adenosylmethionine when incubated with L-methionine. This accumulation of S-adenosylmethionine is correlated with the inhibition of respiration and amino-acid uptake. The inhibition can be reversed by either adenosine or adenosine phosphates but it has been demonstrated that the phosphates are nine has the effect of reducing the amount of adenosine phosphates present in the turnips slices. Feeding with both adenosine and methionine further increases the accumulation of S-adenosylmethionine which is metabolically inactive. It is concluded that methionine inhibits tissue respiration by trapping adenosine as s-adenosylmethionine and so limiting the rate of oxidative phosphorylation.