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At least 559 records · Page 31Linked to original sources
PubMed1982

Peptide transport in rabbit kidney. Studies with L-carnosine.

L-Carnosine was shown to be transported into rabbit renal brush-border membrane vesicles by an Na+ -independent mechanism. The transport was competitively inhibited by glycyl-L-proline. Various di- and tripeptides inhibited L-carnosine transport, whereas free amino acids did not. Inhibition studies showed that blocking the free amino and carboxyl groups of the peptide reduced its affinity for the transport carrier. Under the conditions in which there was no detectable hydrolysis of L-carnosine in the medium, intravesicular contents showed a 30% hydrolysis of the peptide within the vesicles. Disruption of membrane vesicles with deoxycholate resulted in a 3-fold increase in L-carnosine hydrolyzing activity over untreated intact vesicles. Based on these observations, a model for peptide transport is proposed in which transport of the intact peptide across the membrane is followed by its partial or complete hydrolysis by a membrane peptidase whose active site is on the cytoplasmic side of the membrane.

Animals↗
PubMed1975

Macrophage esterase: identification, purification and properties of a chymotrypsin-like esterase from lung that hydrolyses and transfers nonpolar amino acid esters.

A chymotrypsin-like esterase was purified from beef lung. This lysosomal enzyme, not previously characterized, seemed to be composed of two or more forms with molecular weights of about 52 000. It hydrolysed N-benzoyl-DL-phenylalanine beta-naphthol ester at acid and neutral pH; it polymerized L-phenylalanine methyl ester(Phe-OMe) at neutral pH; and it transferred the Phe-residue from Phe-OMe to hydroxylamine at neutral pH. Phenylmethanesulfonyl fluoride, an inhibitor of hydrolytic enzymes with serine in their catalytic site, inhibited this enzyme, but pepstatin, the cathepsin D (EC 3.4.4.23) inhibitor, did not. Sulfhydryl reagents were not required for activity. Macrophages, especially pulmonary alveolar macrophages, were a rich source of this esterase, so it is likely that the enzyme purified from lung came from its macrophages. The esterase hydrolysed and transferred monoamino acid esters, especially those of the aromatic type. Cathepsin C, the dipeptidyl peptide hydrolase (EC 3.4.14.1), acted only on dipeptide esters and amides. Pancreatic chymotrypsin acted on both monoamino acid and dipeptide esters. The chymotrypsin-like esterase did not hydrolyse hemoglobin, casein, or plasma albumin. Thus its proteolytic activity, if present, must be limited to specific substrates, as yet unknown.

Amino Acids↗
PubMed1976

Activation of proenzyme of acidic protease from human seminal plasma.

The kinetics and the extent of the conversion of the proenzyme into the active acidic protease (EC 3.4.23.--) of human seminal plasma were dependent on acidic pH. Between pH 2 and 4, the initial rate of the activation was first-order with respect to the proenzyme. Between pH 4.5 and 5, the rate deviated from the first-order with an initial lag period which can be abolished by adding an excess amount of the acidic protease or pepsin. The extent of the activation was complete between pH 2 and 3 and became incomplete between pH 4 and 5. Addition of the acidic protease or pepsin did not alter the extent of the activation at the high pH values. According to the chromatographic profile on a Sephadex G-75 column, the activation products (namely active acidic protease and an activation peptide) obtained at pH 3 and those obtained at pH 4.5 were identical. The molecular weight of the activation peptide obtained at pH 3 was 6900; its amino acid composition was analyzed and compared with those of the proenzyme and the acidic protease. Remarkable similarity between the amino acid composition of the acidic protease and that of human pepsin was observed. In the presence of an excess amount of hemoglobin, the conversion of the proenzyme was self-activated and showed an initial lag period. Addition of acidic protease did not change the rate of self activation or the lag period.

Amino Acids↗
PubMed1977

Arylamidases of rat liver and chemically induced hepatomas. II. Preparation and characterization of monospecific antisera against two distinct arylamidase-active antigens.

Monospecific antisera were prepared against the most prominent arylamidase (alpha-aminoacyl-peptide hydrolase (microsomal), EC 3.4.11.2) active antigen in plasma membranes (the plasma membrane arylamidase) and lysomal content (the lysosomal content arylamidase), respectively. Plasma membrane extract and lysosomal content were allowed to react in crossed immunoelectrophoresis against their homologous antisera. The electrophoretic plates were washed extensively, dried and subsequently stained for arylamidase activity. The particular immunoprecipitates were thus identified and could be excised to be used for immunizations. The two resulting antisera precipitated the arylamidase used for immunization, but failed to be monospecific as they precipitated additional antigens. These antisera with restricted specificity against some plasma membrane and lysosomal content antigens, respectively, were used to produce immunoprecipitates intended for new attempts to prepare monospecific antisera by a second cycle of immunizations. A monospecific antiserum against the plasma membrane arylamidase was thus obtained, while a third cycle of immunizations was needed to get a monospecific anti-lysosomal content antiserum. The plasma membrane arylamidase showed ATPase activity also after precipitation with the monospecific antiserum, thus still retaining its characteristics as a multienzyme complex.

Aminopeptidases↗
PubMed1981

Purification and substrate characterization of a human enkephalin-degrading aminopeptidase.

A 5000-fold purification of the enzyme responsible for the rapid inactivation of enkephalin in human blood has been achieved: this enzyme cleaves the N-terminal tyrosine from enkephalin and from short peptides provided their first amino acid is aromatic. The enzyme, an enkephalin-degrading aminopeptidase (alpha-aminoacyl-peptide hydrolase, EC 3.4.11.11), requires a free amino group on the substrate and has a maximum activity around pH 8. Its appearance molecular weight is in the range of 80 000-90 000 and an apparent Michaelis constant of 0.4 mM was determined.

Aminopeptidases↗