Functional incorporation and preferred orientation of phytohemagglutinin receptor glycoproteins in phospholipid vesicles

Porcine lymphocyte Phaseolus vulgaris phytohemagglutinin (PHA) receptor glycoproteins purified by affinity chromatography have been reassembled into vesicles made of phosphatidylcholine and phosphatidylserine by detergent (dodecyltrimethylammonium bromide) dialysis. The receptor glycoproteins were incorporated into the lipid vesicles in a nonselective manner with a yield of 65-70%. Vesicles containing the glycoproteins were sealed as evidenced by their impermeability to calcium ions, using quin 2 trapped inside the vesicles. The vesicles were agglutinated by PHA, suggesting that the saccharidic moiety of the reconstituted glycoproteins was, at least in part, oriented towards the extravesicular medium. This observation was further supported by the fact that the vesicles bound 125I-labeled PHA in a specific and saturable manner. At maximum amount of lectin bound, a ratio of 1.01 +/- 0.05 microgram of PHA per microgram glycoprotein incorporated was measured. When the binding data were analyzed by Scatchard plot, a downward concave profile was observed, suggestive of a positive cooperativity at low concentrations of lectin. The orientation of the reconstituted lectin receptor glycoproteins was determined by proteolytic treatments of labeled glycoproteins. The combined action of trypsin and chymotrypsin released, in the 120,000 X g supernatant, approximately 80% of label when 125I-tagged PHA receptor glycoproteins were incorporated into the vesicles. When the oligosaccharidic moieties of the receptor glycoproteins were specifically labeled, the simultaneous action of the two enzymes released approximately 70% of tritium labeling present in the reconstituted system. Taken together, these results suggest that the reconstituted PHA receptors are preferentially oriented into the phospholipid vesicles. The reconstituted PHA receptor glycoproteins competed effectively with cellular receptors in the assay of PHA-induced porcine lymphocyte activation. A 50% inhibition of [3H]thymidine incorporation was observed when 1 microgram of glycoproteins in vesicles was added to the cultured cells, whereas vesicles alone had no effect at this (equivalent) concentration.     

Amino acid sequence of the nonsecretory ribonuclease of human urine

The amino acid sequence of a nonsecretory ribonuclease isolated from human urine was determined except for the identity of the residue at position 7. Sequence information indicates that the ribonucleases of human liver and spleen and an eosinophil-derived neurotoxin are identical or very closely related gene products. The sequence is identical at about 30% of the amino acid positions with those of all of the secreted mammalian ribonucleases for which information is available. Identical residues include active-site residues histidine-12, histidine-119, and lysine-41, other residues known to be important for substrate binding and catalytic activity, and all eight half-cystine residues common to these enzymes. Major differences include a deletion of six residues in the (so-called) S-peptide loop, insertions of two, and nine residues, respectively, in three other external loops of the molecule, and an addition of three residues at the amino terminus. The sequence shows the human nonsecretory ribonuclease to belong to the same ribonuclease superfamily as the mammalian secretory ribonucleases, turtle pancreatic ribonuclease, and human angiogenin. Sequence data suggest that a gene duplication occurred in an ancient vertebrate ancestor; one branch led to the nonsecretory ribonuclease, while the other branch led to a second duplication, with one line leading to the secretory ribonucleases (in mammals) and the second line leading to pancreatic ribonuclease in turtle and an angiogenic factor in mammals (human angiogenin). The nonsecretory ribonuclease has five short carbohydrate chains attached via asparagine residues at the surface of the molecule; these chains may have been shortened by exoglycosidase action.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of lidocaine and pyromecaine on the size of an experimental myocardial infarct

The experiments on rats with a 3-day myocardial infarction caused by the left coronary artery ligation have shown that multiple lidocaine and pyromecaine injections according to a given scheme decrease the size of the necrosis area. Drug effects were not related to their action on the blood supply of the ischemic area.     

Poly(ADP-ribose) polymerase forms loops with DNA

The interaction between highly purified poly(ADP-ribose) polymerase from calf thymus and different topological forms of pBR322 DNA has been studied by gel retardation electrophoresis and electron microscopy. We show that: (i) in the absence of nicks on DNA the enzyme has a marked affinity for supercoiled (form I) DNA, (ii) in the presence of single stranded breaks poly(ADP-ribose) polymerase preferentially binds to form II, (iii) in all cases enzyme molecules are frequently located at DNA intersections, (iv) a cooperative binding of the enzyme on DNA occurs.     

Human endothelin converting enzyme-2 (ECE2): characterization of mRNA species and chromosomal localization.

Generation of the functionally pleiotropic members of the endothelin vasoactive peptide family is critically catalyzed by unique type II metalloproteases, termed endothelin converting enzymes (ECE). Isolation of human ECE-2 (EC 3.4.24.71) cDNAs revealed deduced open reading frames of 787 and 765 amino acids with approximately 60% identity with human ECE-1. Characterization of mRNA variants revealed mRNA structural diversity at the 5'-terminus. Two mRNA species exist containing distinct first and second exons. Furthermore, in one of these species, an in-frame deletion of the intracytoplasmic domain removed 29 amino acids. Because of the previously reported human genetic diseases ascribed to germline mutations of member genes of the endothelin family, ECE2 was localized in human chromosomes with fluorescence in situ hybridization and radiation hybrid mapping to 3q28-q29 and SHGC-20171/D3S1571, respectively.     

Cytosolic protein phosphotyrosine phosphatases from rabbit kidney. Purification of two distinct enzymes that bind to Zn2+-iminodiacetate agarose

Cytosolic protein phosphotyrosine (PPT) phosphatase was measured using a new substrate, Tyr(32P)-labeled bovine serum albumin. Kidney was found as a particularly rich tissue source of PPT-phosphatase activity, containing twice as much as liver and over 10-fold more than brain, heart, lung, or skeletal muscle. An affinity column of Zn2+-iminodiacetate agarose adsorbed up to 60% of the PPT-phosphatase present in kidney extracts. Subsequent chromatography on DEAE-Sepharose separated the phosphatase into two peaks, labeled I and II, that had Mr = 34,000 and 37,000, respectively, upon gel filtration with Sephadex G-75 Superfine. Overall purification of 850- and 1100-fold was achieved with a net 4% yield. Both phosphatases hydrolyzed p-nitrophenylphosphate as well as the protein substrate in the presence of EDTA. Peak I phosphatase activity displayed a neutral pH optimum, had an absolute requirement for sulfhydryl compounds, and was sensitive to trypsin, whereas Peak II activity had an acidic pH optimum and was active without mercaptans. The two proteins also gave different fragmentation patterns by gel electrophoresis after digestion with S. aureus V8 protease. The results show that multiple forms of PPT phosphatase specifically interact with Zn2+ and provide a basis for further structural and functional comparisons among different members of the phosphoprotein phosphatase family.     

Tryptic cleavage and substructure of bovine cardiac myosin subfragment 1

The method of limited tryptic proteolysis has been used to compare and contrast the substructure of bovine cardiac myosin subfragment 1 (S-1) to that of skeletal myosin S-1. While tryptic cleavage of cardiac S-1, like that of skeletal S-1, yields three fragments, the 25K, 50K, and 20K peptides, the digestion of cardiac S-1 proceeds at a 2-fold faster rate. The increased rate of cleavage is due entirely to an order of magnitude faster rate of cleavage at the 25K/50K junction of cardiac S-1 compared to that of skeletal, with approximately equal rates of cleavage at the 50K/20K junctions. Actin inhibits the tryptic attack at this latter junction, but its effect is an order of magnitude smaller for the cardiac than for the skeletal S-1. Furthermore, the tryptic susceptibility of the 50K/20K junction of cardiac S-1 in the acto-S-1 complex is increased in the presence of 2 mM MgADP. This effect is not due to partial dissociation of the cardiac acto-S-1 complex by MgADP. Our results indicate that in analogy to skeletal S-1, the cardiac myosin head is organized into three protease-resistant fragments connected by open linker peptides. However, the much faster rate of tryptic cleavage of the 25K/50K junction and also the greater accessibility of the 50K/20K junction in the cardiac acto-S-1 complex indicate substructural differences between cardiac and skeletal S-1.     

Studies on functional domains of the regulatory subunit of bovine heart adenosine 3':5'-monophosphate-dependent protein kinase

The functional domains of the regulatory subunit of isozyme II of cAMP-dependent protein kinase were studied. It was shown using Edman degradation that the regulatory subunit contained a phosphorylated residue which was very close in primary sequence to the site most sensitive to hydrolysis by low trypsin concentrations as postulated previously (Corbin, J.D., Sugden, P.H., West, L., Flockhart, D.A., Lincoln, T.M., and McCarthy, D. (1978) J. Biol. Chem. 253, 3997-4003). Catalytic subunit incorporated 0.9 mol of 32P from [gamma-32P]ATP into a preparation of regulatory subunit that contained 1.1 mol of endogenous phosphate. After phosphorylation by the catalytic subunit, the regulatory subunit contained 2.2 mol of chemical phosphate. The effects of heat denaturation upon the rate and extent of phosphorylation of the regulatory subunit were compared with the effects of these treatments upon the cAMP binding and inhibitory domains. These data suggested that the regulatory subunit required factors in addition to an intact phosphorylatable primary sequence in order for inhibitory activity to be expressed. Such factors might be part of the secondary or tertiary structure of the protein. These studies are discussed with respect to the mechanism of inhibition of catalytic activity, and a model of the regulatory subunit structure is proposed.