Incorporation of Double-Labeled l -Cystine and dl -Valine in Penicillin

Incorporation of double-labeled L-cystine and DL-valine in penicillin.

l-[3,3'-(3)H]cystine was incorporated into penicillin with retention of one tritium. This result can be explained by beta-lactam formation through ring closure between C3 of cysteine and NH of valine. No radioactivity of dl-[2,3-(3)H]valine was incorporated into penicillin. The loss of isotope at C2 occurs during the inversion of configuration. The loss of label at C3 is discussed in terms of p...

Biosynthesis of penicillins; utilization of deuterophenylacetyl-N15-dl-valine in penicillin biosynthesis.

In Paper I in this series (2) the stimulation of penicillin production by certain compounds containing the phenylacetyl group was reported. It was realized that a stimulation of yield of this biological product following addition of a given substance to the medium may result from any one of several possible metabolic mechanisms. The stimulating substance may act as a vitamin or growth promoter,...

THE EFFECT OF dl-METHIONINE, l-CYSTINE, AND dl-ISOLEUCINE ON THE UTILIZATION OF PARENTERALLY ADMINISTERED DOG HEMOGLOBIN

1. Further observations on the utilization of parenterally administered dog hemoglobin show that oral supplements of dl-methionine and l-cystine improve the efficiency of utilization of hemoglobin N, while a fed supplement of dl-isoleucine alone is without effect. 2. When N-isoleucine is added to a fed supplement of methionine or methionine and cystine, the utilization of parenterally given hem...

Studies on analogues of L-cysteine and L-cystine. I. Some structural requirements for inhibiting the incorporation of radioactive L-cystine by leukemic leukocytes.

Incorporation of radioactive L-cystine by normal and leukemic leukocytes in vivo.

P REVIOUS STUDIES insdicate that L-cyst-eiise or related compounds may be importamst ins the metabolism of leukocytes. Thus L-cysteine, and to a lesser extent homocyst-eimse and glutathione, modify the leukopenia induced by nitrogen mustard.’ . 2 This protective effect appears to be specific in that mamsy highly reactive compoutsds w-ith structures closely related to L-cysteimse fail to prevent...