Generation of multiple forms of methionyl-tRNA synthetase from the multi-enzyme complex of mammalian aminoacyl-tRNA synthetases by endogenous proteolysis

Methionyl-tRNA synthetase occurs free and as high-molecular-weight multi-enzyme complexes in rat liver. The free form is purified to near homogeneity by conventional column chromatography and affinity chromatography on tRNA-Sepharose. The native molecular weight of free methionyl-tRNA synthetase is 64 500, based on its sedimentation coefficient of 4.5 S and Stokes radius of 33 A. The free methionyl-tRNA synthetase apparently belongs to alpha-type subunit structure, since the subunit molecular weight is 68 000, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Methionyl-tRNA synthetase is dissociated from the high-molecular-weight synthetase complex by controlled trypsinization, according to Kellermann, O., Viel, C. and Waller, J.P. (Eur. J. Biochem. 88 (1978) 197-204). The dissociated, free methionyl-tRNA synthetase is subsequently purified to near homogeneity. The subunit structure of dissociated methionyl-tRNA synthetase is identical to that of endogenous free methionyl-tRNA synthetase. Anti-serum raised against Mr 104 000 protein in the synthetase complex, specifically inhibited methionyl-tRNA synthetase in both the free and the high-molecular-weight forms to the same extent. These results suggest that the occurrence of multiple forms of methionyl-tRNA synthetases in mammalian cells may, in part, be due to proteolytic cleavage.

Rat liver histidyl-tRNA synthetase. Purification and inhibition by the myositis-specific anti-Jo-1 autoantibody

Myositis is an autoimmune inflammatory muscle disease of unknown etiology. We demonstrate directly that the antigen to the myositis-specific anti-Jo-1 antibody is histidyl-tRNA synthetase. The anti-Jo-1 antibody inhibits human HeLa and rat liver histidyl-tRNA synthetase. Using conventional and immunoaffinity chromatography with immobilized anti-Jo-1 antibody, we have purified rat liver histidyl-tRNA synthetase which has a subunit Mr 64,000 and an estimated native Mr suggesting an alpha 2 structure. The evidence indicates that the Jo-1 antigen is histidyl-tRNA synthetase, and that some of the histidyl-tRNA synthetase structure are conserved across species.

Association of methionyl-tRNA synthetase with detergent-insoluble components of the rough endoplasmic reticulum

Using fluorescent antibody staining, we have established the association of methionyl-tRNA synthetase with the endoplasmic reticulum in PtK2 cells. After Triton X-100 extraction, 70% of the recovered aminoacyl-tRNA synthetase activity was found in the detergent-insoluble fraction. This fraction of the enzyme remained localized with insoluble endoplasmic reticulum antigens and with ribosomes, which were stained with acridine orange. By both fluorescence microscopy and electron microscopy the organization of the detergent-insoluble residue was found to depend on the composition of the extracting solution. After extraction with a microtubule-stabilizing buffer containing EGTA, Triton X-100, and polyethylene glycol (Osburn, M., and K. Weber, 1977, Cell, 12:561-571) the ribosomes were aggregated in large clusters with remnants of membranes. After extraction with a buffer containing Triton X-100, sucrose, and CaCl2 (Fulton, A. B., K. M. Wang, and S. Penman, 1980, Cell, 20:849-857), the ribosomes were in small clusters and there were few morphologically recognizable membranes. In both cases the methionyl-tRNA synthetase and some endoplasmic reticulum antigens retained approximately their normal distribution in the cell. Double fluorochrome staining showed no morphological association of methionyl-tRNA synthetase with the microtubule, actin, or cytokeratin fiber systems of PtK2 cells. These observations demonstrate that detergent-insoluble cellular components, sometimes referred to as "cytoskeletal" preparations, contain significant amounts of nonfilamentous material including ribosomes, and membrane residue. Caution is required in speculating about intermolecular associations in such a complex cell fraction.

Ocular distribution of liposome-encapsulated epinephrine and inulin in the albino rabbit

A methodology has been developed to evaluate the disposition of liposome-encapsulated epinephrine and inulin in the conjunctival sac and selected ocular tissues. Relative to inulin, epinephrine effluxed much more rapidly from liposomes and disappeared more rapidly from the tear pool. As a result, liposomes were found to exert opposite effects on the ocular uptake of epinephrine and inulin. Over a period of 45 minutes, the concentration of epinephrine in the eye was 1.5 - 3 times lower when presented in liposomes than in aqueous solutions. This contrasted with the 3 to 15 fold increase in inulin concentration in the eye from liposomal preparations of the compound. Specifically, much of the increase in inulin concentration in the cornea can be attributed to an increase seen in the epithelium. Despite elevated inulin concentrations in the ocular tissues it bathes, the aqueous humor was devoid of inulin unless the corneal epithelium was physically removed prior to topical dosing. Collectively, these findings suggest that both the manner in which an entrapped compound interacts with the constituents of liposomes and the manner in which liposomes interact with the absorptive surfaces of the eye can significantly influence its pharmacokinetics in the eye.

Stoichiometry and composition of an aminoacyl-tRNA synthetase complex from rat liver

The particulate aminoacyl-tRNA synthetases of rat liver were copurified about 1000-fold with more than 20% yields for individual synthetase activities. Measurements of aminoacylation activities showed that lysyl-, arginyl-, leucyl-, isoleucyl-, and methionyl-tRNA synthetases in the purified complex cosedimented at 18 S. The molecular weight of the synthetase complex is about one million, as estimated by gel filtration. The stoichiometry of the synthetase in the complex was determined by active site titration with aminoacyl adenylates. Results indicate that the 18S synthetase complex contains one subunit of methionyl-tRNA synthetase and two subunits of lysyl-tRNA synthetase. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed that the 18S synthetase complex contains eight major protein bands. Proteins with subunit molecular weights of 104,000, 92,000, 69,000, and 67,000 are present in molar ratios of 1:1:2:2, while proteins with subunit molecular weights of amounts. These results suggest that the particulate aminoacyl-tRNA synthetases exist as a heterotypic multienzyme complex with defined structure.

An approach to the elucidation of metabolic breakdown products of the luteinizing hormone-releasing hormone

Metabolic breakdown of the luteinizing hormone-releasing hormone (LH-RH) could lead to the following fragments containing pyroglutamic acid: pyroglutamic acid (1), pGlu-His (2), pGLu-His-Trp (3), pGlu-His-Trp-Ser (4), etc., and finally pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly (10). We have synthesized fragments 2-10 and successfully separated all ten metabolites and LH-RH by high-performance liquid chromatography (HPLC) with a muBondapak C18 column. In a test of the viability of the method, cochromatography of fragments 1-10 and LH-RH with the products of chymotryptic digestion of tritiated LH-RH showed radioactive peaks corresponding to the expected products, fragments 3 and 5. Analysis of the products of incubation of a rat kidney homogenate supernatant with LH-RH showed fragments 1-4 and LH-RH. The finding of breakdown at position 4 uncovers a new site of LH-RH breakdown and points the way to the design of potential LH-RH antagonists and agonists where the 4 position would be substituted with unnatural amino acids to prevent breakdown.

Mitogenicity and binding properties of beta-galactoside-binding lectin from chick-embryo kidney

THe beta-galactoside-binding lectin binds to glucosamine, mannosamine and galactosamine in addition to beta-galactoside, as determined by the inhibition of haemagglutination. Haemagglutination is further extended to examine the interaction of the binding sites for hexosamines and beta-galactosides, indicating that the binding of hexosamine and beta-galactoside is competitive. The lectin also shows strong mitogenic activity toward lymphocytes from mouse lymph node, as determined by the stimulation of thymidine incorporation.

Some analogues of luteinizing hormone-releasing hormone with substituents in position 10

As part of our studies on the design of agonists of the luteinizing hormone-releasing hormone (LH-RH), we have synthesized the [des-Gly-NH2(10)]-LH-RH N-methylhydrazide (1), the corresponding thiosemicarbazide (2), and the N-formyl- (3) N-acetyl- (4) and N-(trifluoroacetyl)hydrazide (5). Analogue 1 may be regarded as isosteric with [des-Gly-NH2(10)]-LH-RH N-alkylamides which are, in general, potent agonists. Analogues 2-5 may be regarded as isosteric with [aza-Gly-NH2(10)]-OH-RH, which is equipotent with the hormone. The required protected intermediates were prepared by solid-phase synthesis, and the free peptides were prepared from them by deprotection with HF, followed by purification on Sephadex G-25. Bioassay of these analogues with rat hemipituitaries in vitro showed the following values as percentages of the hormonal values for the release of LH and FSH respectively: N-methylhydrazide (1), 17 and 11%; semithiocarbazide (2), 6.5 and 4.6%; N-formylhydrazide (3), 15.3 and 10%; N-acetylhydrazide (4), 1.2 and 0.6%; N-(trifluoroacetyl)hydrazide (5), 1.0 and 0.9%. Thus, these types of isosteric substitutions are inimical to the preservation of the high biological activity of LH-RH.

Purification and characterization of lysyl-tRNA synthetase after dissociation of the particulate aminoacyl-tRNA synthetases from rat liver

The major aminoacyl-tRNA synthetase complex (the 24 S complex) isolated from rat liver, which contains lysyl-, leucyl-, and arginyl-tRNA synthetase activities, is dissociated into fully active free aminoacyl-tRNA synthetases by column chromatography on diaminooctyl-Sepharose. During the hydrophobic interaction chromatography, more than a quantitative yield of the lysyl-tRNA synthetase activity is obtained. The free lysyl-tRNA synthetase, dissociated from the synthetase complex, is purified about 2,000-fold with a 13% yield by conventional column chromatography. Lysyl-tRNA synthetase is also purified from the 24 S synthetase complex by affinity column chromatography on lysyl-diaminohexyl-Sepharose. Free lysyl-tRNA synthetase as dissociated from the synthetase complex, is evidently a dimeric enzyme with a subunit molecular weight of 66,000 +/- 3,000, as determined by gel electrophoresis, sucrose gradient centrifugation and gel filtration.

Aneurysm of the inferior mesenteric artery

Current diagnostic techniques make it possible to diagnose unsuspected aneurysms. Two unsuspected cases of aneurysms of the inferior mesenteric artery are reported. One was iatrogenic and represented a false aneurysm of the proximal end of the inferior mesenteric artery following resection of an abdominal aortic aneurysm. The second was an aneurysm of the proximal protion of the inferior mesenteric artery in a patient with occlusion of the celiac axis, superior mesenteric artery and left ileofemoral system. The authors believe this to be the first published aneurysm of the inferior mesenteric artery.

Disassembly and gross structure of particulate aminoacyl-tRNA synthetases from rat liver. Isolation and the structural relationship of synthetase complexes

The major high molecular weight complex of aminoacyl-tRNA synthetases is purified about 1000-fold with 30% yield from rat liver. The synthetase complex sediments at 24 S with a molecular weight of 900,000 +/- 75,000 and contains aminoacylation activities for lysine, arginine, isoleucine, leucine, methionine, glutamine, glutamate, and proline. The 24 S synthetase complex dissociates into 21 S, 18 S, 13 S, 12 S, and 10 S complexes with specific enzymatic activities. Dissociation of the 24 S complex into active free synthetases is achieved by hydrophobic interaction chromatography. The disassembly of the synthetase complex is consistent with the structural model of a heterotypic multienzyme complex and suggests that the complex formation is due to the specific intermolecular interactions among the synthetases.

Adenosine cyclic 3',5'-monophosphate-dependent protein kinase from human platelets

A single cyclic AMP-dependent protein kinase (EC 2.7.1.37) has been isolated from human platelets by using DEAE-cellulose ion-exchange chromatography and Sephadex G-150 gel filtration. The molecular weight of the protein kinase was estimated to be 86 490. In the presence of cyclic AMP, the protein kinase could be dissociated into a catalytic subunit of molecular weight 50 000, and either one regulatory subunit of molecular weight 110 000 or two regulatory subunits of molecular weights 110 000 and 38 100, depending on the pH used. Recombination of either of the regulatory subunits with the catalytic subunit restored cyclic AMP-dependency in the catalytic subunit. The apparent Km for ATP in the presence of 10 muM Mg2+ was 4 muM (plus cyclic AMP) and 4.3 muM (minus cyclic AMP). The concentration of cyclic AMP needed for half-maximal stimulation of the protein kinase was 0.172 muM and apparent dissociation constants of 3.7 nM (absence of MgATP) and 0.18 muM (presence of MgATP) were exhibited by the "protein kinase-cyclic AMP complex". The enzyme required Mg2+ for maximum activity and showed a pH optimum of 6.2 with histone as substrate. In addition to four major endogenous platelet protein acceptors of apparent molecular weights 45 000, 28000, 18 500, and 11 100, the platelet protein kinase also phosphorylated the exogenous acceptor proteins thrombin, collagen and histone, all capable of inducing platelet aggregation. Prothrombin, a nonaggregating agent, was not phosphorylated.