THE DIAGNOSTIC VALUE OF SERUM LEUCINE AMINOPEPTIDASE

Serum leucine aminopeptidase determination was found to be a useful screening procedure for hepatobiliary disease in jaundiced and unjaundiced patients. Values under 1,000 units are of no help in the differential diagnosis of jaundice but values above 1,000 units are highly indicative of biliary obstruction. The differentiation of intra- from extrahepatic obstruction as well as of malignant from benign jaundice cannot generally be established by this single test.

THE ISOLATION OF AMINO ACIDS FROM MIXTURES AS THEIR N-2,4-DINITROPHENYL DERIVATIVES, METHIONINE, LEUCINE, PHENYLALANINE, ORNITHINE, LYSINE AND TYROSINE

1. The separation of the dinitrophenyl derivatives of methionine, leucine (together with isoleucine), phenylalanine, ornithine, lysine and tyrosine from each other, and from the dinitrophenyl derivatives of the other protein amino acids, by partition chromatography on columns is described. 2. The harmful effect on resolving power of using too close-fitting a packing tool in preparing these partition columns is indicated and the dimensions needed to obtain good resolution are given.

RESISTANCE OF ESCHERICHIA COLI TO TETRACYCLINES

1. A strain of Escherichia coli highly resistant to chlortetracycline and partially cross-resistant to tetracycline has been isolated. 2. The nitro-reductase system of the resistant cells was inhibited to a smaller extent by chlortetracycline than was the corresponding enzyme of sensitive cells. 3. The incorporation of leucine in vitro into the ribosomal protein of cell-free preparations from sensitive and resistant cells was equally inhibited by chlortetracycline. 4. Resistant cells accumulated much less chlortetracycline and tetracycline than did sensitive cells when both were cultured in the presence of these drugs. 5. The uptake of tetracycline by both sensitive and resistant E. coli was dependent on the presence of glucose in the medium. 6. Fractionation of cells cultured in medium containing [(14)C]chlortetracycline indicated that the largest proportion of radioactivity in sensitive cells was in the fraction consisting mainly of cell-wall material. There was no concentration of radioactivity in any one fraction of the resistant cells. 7. No evidence could be obtained for a specific tetracycline-excretion system in the resistant cells. 8. The significance of these results in relation to current theories of the antibiotic action of and resistance to the tetracycline drugs is discussed.