Extracellular Amino Acid Concentrations in the Dorsal Spinal Cord of Freely Moving Rats Following Veratridine and Nociceptive Stimulation

In vivo microdialysis was used to sample extracellular concentrations of amino acids in the dorsal lumbar spinal cord of freely moving rats. Changes in the extracellular concentrations of amino acids were measured in response to infusion of veratridine (180 microM), a sodium channel activator, as well as during acute noxious stimulation by an injection of 5% formalin into the metatarsal region of the hindleg. Veratridine produced a tetrodotoxin (TTX)-sensitive increase in the extracellular concentration of Glu. Concentrations of Asp, taurine, Ala, Asn, and Gly were not significantly elevated following veratridine stimulation. Intradermal injection of formalin produced a TTX-sensitive increase in Asp concentration and a non-TTX-sensitive increase in Glu concentration. These data support the hypothesis that Glu and Asp are dorsal horn neurotransmitters involved in nociception.     

Folding of thermolysin fragments. Identification of the minimum size of a carboxyl-terminal fragment that can fold into a stable native-like structure

The COOH-terminal cyanogen bromide fragment 206-316 of thermolysin has been shown to possess protein domain characteristics that are able to refold into a stable native-like structure (Fontana et al., 1982). We now report the results of limited proteolysis of this fragment with the aim of identifying the minimum size of a COOH-terminal fragment of thermolysin that is able to fold by itself. Proteolysis with subtilisin, chymotrypsin, thermolysin and trypsin allowed us to isolate to homogeneity eight different subfragments, which can be grouped in two sets of peptides, i.e. (218-222)-316 and (252-255)-316. These subfragments are able to acquire a stable conformation of native-like characteristics, as judged by quantitative analysis of secondary structure from far-ultraviolet circular dichroism spectra and immunochemical properties using rabbit anti-thermolysin antibodies. In addition, even the smallest fragment isolated (sequence 255-316) shows co-operative and reversible unfolding transitions mediated by heat (tm 65 degrees C) and guanidine hydrochloride (midpoint transition at 2.5 M denaturant), as often observed with globular proteins. From the kinetics of the proteolytic digestion and analysis of the isolated subfragments, it is concluded that proteases lead to a stepwise degradation of fragment 206-316 from its NH2-terminal region, leading to the highly helical fragment (252-255)-316, quite resistant to further proteolytic digestion. The results of this study provide evidence that it is possible to isolate stable supersecondary structures of globular proteins and correlate well with predictions of subdomains of the COOH-terminal structural domain of thermolysin.     

Hierarchic organization of globular proteins: Experimental studies on thermolysin

Previous studies from this laboratory have shown that the thermolysin fragment 121–316, comprising entirely the“all-α” COOH-terminal structural domain 158–316, as well as fragment 206–316 (fragment FII) are able to refold into a native-like, stable structure independently from the rest of the protein molecule. The present report describes conformational properties of fragments 228–316 and 255–316 obtained by chemical and enzymatic cleavage of fragment FII, respectively. These subfragments are able to acquire a stable conformation of native-like characteristics, as judged by quantitative analysis of secondary structure from far-ultra-violet circular dichroism spectra and immunochemical properties using rabbit anti-thermolysin antibodies. Melting curves of the secondary structure of the fragments show cooperativity with a temperature of half-denaturationT _mof 65–66°C. The results of this study provide evidence that it is possible to isolate stable supersecondary structures (folding units) of globular proteins and correlate well with predictions of subdomains of the COOH-terminal structural domain 158–316 of thermolysin.     

Independent folding of the carboxyl-terminal fragment 228-316 of thermolysin

The COOH-terminal fragment 206-316 of thermolysin was shown previously to maintain a stable folded structure in aqueous solution comparable to that of the corresponding region in native thermolysin and thus to possess protein domain characteristics [Fontana, A., Vita, C., & Chaiken, I. M. (1983) Biopolymers 22, 69-78]. In order to study the effect of polypeptide chain length on folding and stability of an isolated domain, the 111 amino acid residue fragment was shortened on the NH2-terminal side by removal of a 22-residue segment. Treatment of fragment 206-316 with hydroxylamine under alkaline conditions permitted selective cleavage of the Asn227-Gly228 peptide bond, and from the reaction mixture fragment 228-316 was isolated in homogeneous form. This fragment appeared to attain in aqueous solution the folding properties of the corresponding segment in the intact protein, as indicated by quantitative analysis of secondary structure from far-ultraviolet circular dichroism spectra and immunological properties. Thus, double-immunodiffusion analyses showed that fragment 228-316 is able to recognize and precipitate anti-thermolysin antibodies raised in rabbits with native thermolysin as immunogen. The fragment displayed fully reversible and cooperative conformational transitions mediated by pH, heat, and guanidine hydrochloride (Gdn.HCl), as expected for a globular protein species. Thermal denaturation of the fragment in aqueous solution at pH 7.8 showed a Tm of 66 degrees C and the Gdn.HCl-mediated unfolding a midpoint transition at 2.2 M denaturant concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

NAD biosynthesis in human placenta: purification and characterization of homogeneous NMN adenylyltransferase.

Nicotinamide mononucleotide (NMN) adenylyltransferase has been purified to homogeneity from human placenta. The purification procedure consists of several chromatographic steps, including dye-ligand, adsorption, and hydrophobic interaction chromatography. The final enzyme preparation is homogeneous as judged by a single silver stainable band on both nondenaturating and denaturating polyacrylamide gels. The native enzyme shows a molecular weight of about 132,000, as determined by gel filtration on a Superose 12 HR 10/30 fast protein liquid chromatography column. The protein possesses a quaternary structure and is composed of four apparently identical M(r) 33,000 subunits. Isoelectrofocusing experiments give multiple pI values ranging from pH 4.7 to 6.6. Optimum pH study shows a plateau extending from pH 6.0 to pH 9.0. Km values for NMN, ATP, NAD+, and PPi are 38, 23, 67, and 125 microM, respectively. Kinetic analysis reveals a behavior consistent with an ordered sequential Bi-Bi mechanism. Among several metabolites tested only ADP-ribose and beta-NMNH were found to significantly inhibit the enzyme activity.     

Dystrophin predominantly localizes to the transverse tubule/Z-line regions of single ventricular myocytes and exhibits distinct associations with the membrane

Dystrophin is a high molecular weight protein present at low abundance in skeletal, cardiac and smooth muscle and in trace amounts in brain. In skeletal muscle, dystrophin is uniformly distributed along the inner surface of the plasma membrane. Biochemical fractionation studies have shown that all detectable skeletal muscle dystrophin is tightly associated with a complex of wheat germ agglutinin (WGA)-binding and concanavalin A (Con A) binding sarcolemmal glycoproteins. Absence of dystrophin is the primary biochemical defect in patients with Duchenne muscular dystrophy and leads to segmental necrosis of their skeletal myofibers. Although present in similar amounts in normal cardiac and skeletal muscle, the absence of dystrophin from cardiac muscle has less severe effects on the survival of cardiac cells. We have therefore examined whether there are differences in the properties of cardiac and skeletal dystrophin. We report that in contrast to skeletal muscle, cardiac dystrophin is distributed between distinct pools: a soluble cytoplasmic pool, a membrane-bound pool not associated with WGA-binding glycoproteins and a membrane-bound pool associated with WGA-binding glycoproteins. Cardiac dystrophin was not associated with any Con A binding glycoproteins. Immunohistochemical localization studies in isolated ventricular myocytes reveal a distinct punctate staining pattern for dystrophin, approximating to the level of the transverse tubule/Z-line and contrasting with the uniform sarcolemmal staining reported for skeletal muscle fibers. The distinct properties of cardiac dystrophin suggest unique roles for this protein in cardiac versus skeletal muscle function.Abbreviations Dys Dystrophin - T-tubule Transverse tubule - SDS-PAGE Sodium Dodecyl Sulphate-Polyacrylamide Gel Electrophoresis - WGA Wheat Germ Agglutinin - Con A Concanavalin A - DHP Dihydropyridine receptor - FITC Fluorescein Isothiocyanate Conjugate - NAG N-Acetyl-D-Glucosamine - NP-40 NONIDET P-40 - PBS Phosphate-Buffered Saline - TBST Tris Buffered Saline-Tween     

Inactivation of uridine nucleosidase in yeast. Purification and properties of an inactivating protein.

It has been previously demonstrated in our laboratory that uridine nucleosidase (EC 3.2.2.3) is subjected in yeast to inactivation. An inactivating fraction has been isolated and purified to homogeneity with a procedure which includes gel filtration, adsorption chromatography, and electrofocusing techniques. The molecular weight of the enzyme, estimated either by sodium dodecyl sulfate disc gel electrophoresis or by gel filtration is approximately 44,000. No quaternary structure was evidenced. The inactivating activity possesses proteolytic activity against casein and hemoglobin with pH optima of 2.5 and 3.2, respectively. The optimal pH for uridine nucleosidase inactivation is around 4.7. The inactivating activity as well as the proteolytic activity of the preparation can be inhibited by IA but not by IB2 and IC, yeast macromolecular inhibitors for proteinase A (EC 3.4.23.8), B (EC 3.4.22.9), and C (EC 3.4.12.8), respectively. The apparent isoelectric point is pH 4.03. The carbohydrate content is 8.5%. A comparison of the properties of the inactivating protein with those of known yeast proteinases leads to the conclusion that it is identical with the enzyme previously designated as proteinase A, which for the first time has been obtained homogeneous and characterized. It has been shown that proteinase A could play a physiological role in the uridine nucleosidase inactivation process when it is associated, as a complex, with proteinase B.