A " N NMR Study on D - Lysine Metabolism in Neurospora cmssa

The metabolic relationship of D-lysine, L-lysine, and L-pipecolic acid has been investigated in Neurospora c m s s a Kinetic experiments show that radioactivity from D-lysine is efficiently incorporated into L-pipecolic acid and that this metabolite is converted to L-lysine. The a-amino group from D-[cu-"N]lysine is lost in the course of its conversion to L-pipecolic acid and is trapped by pyruvate and a-keto glutarate to give ~-[a"N]alanine and L-[a-"NIglutamic acid. These amino acids are devoid of any label, however, when D-[e-'6N]lysine is applied to the fungus. As determined by mass and "N NMR spectrometry the label from D-[€-"N]lySine migrate via L-pipecolic acid into the a position of L-lysine, Le. D-[e-"NJlysine is converted to L-[a-'%Jlysine. L-Pipecolic acid functions as an intermediate in this conversion. which then gives rise to L-pipecolic acid (Fig. 2). This reaction sequence has been postulated as part of a scheme which is "peculiar to and generalized among yeasts and fungi" (24). In an attempt to distinguish between these two schemes we have prepared ~-[a-"N]lysine and ~-[~'~N]lysine a d applied each substrate to our N. crassa wild type strain. If the scheme depicted in Fig. 1 were operative, I5N from the a position of D-lysine would be removed (step 1 + 2) during the conversion to L-lysine, whereas if the scheme shown in Fig. 2 were operative, the 15N should be retained in the a position of Llysine (step 1 7) (25). 15N label from the E position of Dlysine, however, should migrate into the a position of L-lysine in the first case (Fig. l), whereas in the second case (Fig. 2) it should be found in the E position of L-lysine. Since I5N NMR spectrometry of amino acids became available recently (26), this technique was used to investigate this problem.