The following possibilities present themselves as an explanation for the more effective utilization of the asparagine peptides and aspartic acid as compared to that of asparagine : (a) asparagine peptides may be deamidated with greater ease than asparagine, and the resulting pep tide split into the diearboxylic acid and glycine by peptidases ; (b) the peptides and aspartic acid may be taken up by the microbial cell at a more rapid rate than the free amide ; (c) the asparagine peptides fulfil a need of this organism for naturally-occurring asparagine peptides, or meet the conditions under which the peptides themselves or the asparaginyl radical may most readily be utilized. In an attempt to explore these possibilities, the deamidation of the peptides by chemical means was studied. Upon acid hydrolysis, the asparagine peptides, very surprisingly, proved to be more labile than the free amide. The finding that glycylglutamine is more stable than glutaminylglycine or glutamine was confirmed (see table, col. 3)5.When the glutamine or asparagine peptides were incubated with resting cells of L. mesenteroides, considerable liberation of ammonia occurred. No ammonia beyond the blank values was found in the case of the unsubstituted amides (see table, col. 1). AMMONIA LIBERATED (AS PER CENT OP TOTAL AMIDE) FROMASPARAGINE, GLOTAMira AND THEIR PEPTIDES BY INCUBATION WITH L. mesenteroides AND BY ACID HYDROLYSISCompound L. mesenteroides 1 o per cent Trichloroacetic acid Asparagine G lycyJasparagine AsparaginylglycineGlutamine Glycylglutamine Glutanjinylglycine 0 14 34 96 26 900 6 12 85 39 76 8 25 2092 3798(1)liesting cells (washed twice with saline) of L. mesenteroides (approx. 5 mgm. dry weight) incubated with 4 micromoles of compound in 4 ml. of 31/15 phosphate buffer (pH 6-5), 35?, for 2 hr. (2)Same as (?) \th 5 mgm. of glucose added. (3)Compounds in 10 per cent trichloroacetic acid for 1 hr. at 70?. Ammonia determined titrimetrically after aeration.It has been found previously that resting cells of Strep, hcerholyticus (Richard's)8 and L. arabinosus1 are only able to liberate ammonia from glutamine when they are permitted to glycolyse. Therefore, the degradation of glutamine and asparagine and their peptides was studied with resting cells of L, mesenteroides in the presence of glucose. While some ammonia developed from the free amides under these conditions, practically all the amide nitrogen was liberated from the peptides, if it can be assumed that the ammonia evolved results from deamidation (see table, col. 2). Although the metabolic pathway of the compounds has not been established under these particular conditions, the results clearly indicate that the glutamine and asparagine peptides are metabolized at a much more rapid rate than the corresponding free amides by resting cells of L. mesenteroides, both in the presence and absence of glucose. Similar results for asparagine and its peptides were obtained with resting cells of L. arabinosus. The preferential degradation of the asparagine peptides when compared with that of asparagine is in accord with the previously observed differences in ability of these compounds to support the growth of L. mesenteroides2 The effect of differences in the rate of uptake of the peptides and the free amides by the cells on their metabolic degradation cannot be assessed at present. The enzyme systems of the micro-organisms studied may be better adapted for dealing with the peptides than with the free amide. The possibility should be considered that the effect of simultaneous glucose metabolism might consist in the transformation of the free amides and possibly the peptides themselves into intermediates (specific peptides?) susceptible to rapid metabolic utilization. Considerable clarification of this problem may be expected from a study of the enzyme systems in cell-free extracts.We are indebted to the Rockefeller Foundation and the National Vitamin Foundation for the support of this work.