ELECTROPHORETIC EVIDENCE FOR ISOZYMES OF ARYLAMIDASE ("AMINOPEPTIDASE") IN THE RAT. I. RENAL, SERUM AND URINARY ENZYMES SPLITTING DL-ALANYL-2-NAPHTHYLAMIDE AND L-LEUCYL-2-NAPHTHYLAMIDE

Bilateral nephrectomy elicited no changes of serum blood levels of arylamidase assayed with two chromogenic substrates (l-leucyl-2-naphthylamide and dl-alanyl-2-naphthylamide) two days after the operation. Since rat urine contains similar enzymes it was postulated that the urinary enzyme is of renal origin and distinct from serum arylamidase. For this purpose, electrophoretic studies were undertaken. Starch block (for quantitative determinations) and starch gel for zymograms of arylamidase were used. It was shown that both procedures demonstrated the identity of urinary and renal arylamidase, which was distinct from the serum enzyme. The renal and urinary enzyme showed two distinct isozymes: one remaining at the origin and the other migrating somewhat less than the isozyme in serum. It is postulated that the isozyme remaining at the origin corresponds to a membrane-bound form, whereas the electrophoretically-mobile isozyme is found in the cellular supernatant fraction. The arylamidase from serum was represented by a single enzyme which migrated farthest towards the anode.

Histochemical procedures for the demonstration of arylamidase activity in tissues at the light microscopic level permit the localization of enzyme(s) that can hydrolyze synthetic chromogenic naphthylamides containing l-leucyl and dl-alanyl groups (1).

Rat kidneys have a high concentration of histochemically demonstrable arylamidase in the proximal convoluted tubules (2). Blood levels of arylamidase in the normal adult rat vary within a narrow range (3). The observation of arylamidase activity in rat urine raised several questions that led to the studies which are the basis of the present report.

The relationship of serum and urinary arylamidase was the starting point of this investigation. It was speculated that if the urinary enzyme had its origin in the serum, bilateral nephrectomy should alter blood levels of the enzyme. If no such changes occurred, this would suggest that the urinary enzyme was released from the proximal convoluted tubule. In fact, total renal ablation led to no significant variation of serum arylamidase activity.

It was therefore postulated that urinary arylamidase originated in the kidneys and that both are distinct from serum arylamidase. To test this hypothesis, zone electrophoretic studies were undertaken using two different supporting media. It will be shown that distinct molecular forms or isozymes of arylamidase can be separated from rat tissues and fluids by differential electrophoretic mobility. The electrophoretic identity of urinary and renal arylamidase, both of which are distinct from the serum arylamidase, is demonstrated in this study.

TRANSFER OF EPISOMIC ELEMENTS TO PROTEUS. II. NATURE OF LAC+ PROTEUS STRAINS ISOLATED FROM CLINICAL SPECIMENS

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.), J. A. Wohlhieter, R. V. Citarella, and L. S. Baron. Transfer of episomic elements to Proteus. II. Nature of lac(+)Proteus strains isolated from clinical specimens. J. Bacteriol. 88:1598-1601. 1964.-Strains of Proteus mirabilis exhibiting the unusual property of utilizing lactose (lac(+)) have been reported in clinical material. A genetic examination discloses that the lac(+) determinants in these Proteus strains are associated with an infectious element, P, which is distinct from the sex factor of Escherichia coli K-12. The composite genetic element, P-lac, is readily transmissible to other enteric species and possesses properties which conform to those of an episomic element of the transfer variety. CsCl density-gradient studies of deoxyribonucleic acid (DNA) extracted from lac(+)P. mirabilis indicate that the P-lac(+) element did not arise in this species, but was acquired from an organism possessing a markedly different DNA base composition.

PEPTIDE SYNTHESIS FROM AMINO ACIDS IN AQUEOUS SOLUTION

Four dipeptides and a tripeptide were formed when an aqueous solution of glycine and leucine was exposed to ultraviolet light in the presence of cyanamide.

THE RELATION BETWEEN THE INTRACELLULAR RIBONUCLEIC ACID DISTRIBUTION AND AMINO ACID INCORPORATION IN THE LIVER OF THE DEVELOPING CHICK EMBRYO

The RNA-P and DNA-P content of the nucleus and the RNA-P content of the whole cell of the livers of 8- to 20-day chick embryos and of adult fowls have been determined. The DNA-P content of the liver nuclei was slightly higher in the 8- and 10-day embryo than in all the other stages examined. A significant decrease in the RNA content of the cell occurred during embryonic development. The RNA content of the adult cell was the same as that of the 14- to 16-day embryo. The proportion of the cellular RNA contributed by the nucleus also decreased during development. In respect to both nuclear RNA content and distribution of RNA between nucleus and cytoplasm, the adult resembled the 8- to 12-day embryo. Examination of the fine structure of the cell showed that, as development progressed, free ribosomes decreased in number and the rough membranes increased. Slices of 8-, 14-, and 20-day embryonic livers and of adult livers were incubated with ¹⁴C-leucine, and the amount of labeled amino acid incorporated into whole tissue protein and into the proteins of the subcellular fractions was measured. Embryonic liver incorporated ¹⁴C-leucine 15 to 30 times more rapidly than adult liver. The microsomal protein was always more highly labelled than the protein in any other subcellular fraction; however, in the 8-day embryonic and the adult liver the proportion of total counts found in the nuclear fraction was considerably higher than in the 14- or 20-day embryonic liver. The significance of an apparent correlation between the proportion of the cell's RNA contributed by the nucleus and the proportion of total counts in the nuclear fraction is discussed.