N-Dithiasuccinoyl (Dts)-glycine: A novel oxidation reagent for the formation of intramolecular disulfide bridges under mild conditions

Summary Specific intramolecular cyclization to form disulfide bridges in peptides represents a major challenge to the synthetic art. The N-dithiasuccinoyl (Dts) function was originally proposed as an amino protecting group, removable under mild conditions by thiolysis [Barany, G. and Merrifield, R.B., J. Am. Chem. Soc., 99 (1977) 7363; 102 (1980) 3084]. We demonstrate here that this chemistry can be inverted, i.e., Dts-amines can be used as mild oxidation reagents that promote formation of intramolecular disulfide bridges. With oxytocin and deamino-oxytocin as models, and with Dts-glycine as the oxidant, we have shown the efficacy of this method under a variety of conditions: both components in solution; dithiol-peptide on a polymeric support and Dts-glycine in solution; and soluble dithiol-peptide with Dts-glycyl-resin. Kinetics have been determined under a range of conditions in mixtures of acetonitrile-phosphate buffer. The logarithm of the reaction rate (based on a simplified first-order assumption) varies linearly with pH; the slope of these correlations is 0.68±0.02. Under suboptimal conditions, by-products have been observed that include parallel and antiparallel dimers as well as trisulfide analogues. Optimized conditions give good yields and purities of the desired disulfides. Particular advantages of this approach include the lack of reactivity of Dts-glycine with all non-sulfhydryl side-chain functionalities found in peptides, and the fact that Dts-mediated oxidation is irreversible.This work was taken in part from the Ph.D. Thesis of L. Chen, University of Minnesota, Minneapolis, MN, U.S.A., January 1997 (in preparation). Preliminary reports of this work were made at the 14th American Peptide Symposium, Columbus, OH, U.S.A., June 18–23, 1995 (poster P-119), and at the Fourth International Symposium on Solid Phase Synthesis & Combinatorial Chemical Libraries, Edinburgh, Scotland, U.K., September 12–16, 1995 (Ref. 18).     

Methionine anchoring applied to the solid-phase synthesis of lysine-containing 'head-to-tail' cyclic peptides

Summary Lysine-containing ‘head-to-tail’ cyclic peptides can be prepared via a side-chain anchoring solid-phase synthesis strategy. A handle is prepared using a methionine residue, theC ^α-carboxyl of which forms an, amide with theN ^ε-amine of lysine. Subsequently, the linear peptide sequence is assembled, appropriate deblocking steps are carried out, and on-resin head-to-tail cyclization follows. Optionally, acid-labile protecting groups may be removed while the peptide remains resin-bound. The final cleavage step uses CNBr, and releases the free or protected cyclic peptide into solution. Taken in part from the Ph.D. Thesis of J. C. Kappel, University of Minnesota, November 2003. Portions of this work were reported in preliminary form at the Eighteenth American Peptide Symposium, Boston, MA, U.S.A., 19–23 July 2003, and at the Eighth International Symposium on Solid Phase Synthesis and Combinatorial Chemical Libraries, London, England, U.K., 2–5 September 2003.     

Synthesis and characterization of branched phosphopeptides: Prototype consolidated ligands for SH(32) domains

Summary This paper details the solid-phase synthesis by N -9-fluorenylmethyloxycarbonyl (Fmoc) chemistry of a series of bivalent consolidated ligands, branched peptides with lengths of 22 to 25 residues. The target peptides were designed to, and in fact do, interact with greater specificity and higher affinity with the SH2 and SH3 domains of Abelson kinase in an SH(32) dual domain construct. Fmoc-O-phospho-l-tyrosine[Fmoc-Tyr(PO₃H₂)-OH] was used to introduce the required phosphotyrosine residues, and Fmoc-N -1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl-l-lysine [Fmoc-Lys(Dde)-OH] was used to introduce a branch point that allowed proper orientation of individual ligands. The resultant product peptides were characterized by amino acid analyses and electrospray mass spectra.This paper is based on a presentation given at the Symposium on Peptide Structure and Design as part of the 31st Annual ACS Western Regional Meeting held in San Diego, CA, USA, October 18–21, 1995.     

Using cyclic peptide mixtures as probes for metal ion host-guest interactions

Summary Mixtures of cyclic peptides, formed by head-to-tail cyclizations of side-chain resin-bound linear sequences, have been prepared using solid-phase synthesis. Fast atom bombardment mass spectrometry of cyclic peptides with various metal ions can reveal preferred modes of host-guest patterns, albeit in a nonquantitative manner. This approach could prove useful for more rapid screening of potential peptide ionophores. A cyclic heptapeptide with a dipeptide tail proved to be a particularly effective host for a Ca²⁺ ion; in a small three-component mixture, cyclo[Gly-Asp-d-Pro-Xxx-Asp-d-Pro-Asp(Aca-Phe-NH₂)], binding to Ca²⁺ varied from Xxx=N-MeAla>GlySar. In a 15-component mixture, cyclo[Pro-Xxx-Asn-Pro-Xxx-Asn] where Xxx=Ala, Glu, Leu, Lys or Phe, there were no significant differences with respect to binding to metal ions. We believe this to be the first reported use of cyclic peptide libraries for screening metal ions to discern host-guest relationships.Abbreviations Aca aminocaproic acid - Boc tert-butyloxycarbonyl - BOP benzotriazolyloxy-tris(dimethylamino)phosphonium hexafluorophosphate - DCM dichloromethane - DIEA diisopropylethylamine - DMF N,N-dimethylformamide - ESI electrospray ionization - FABMS fast atom bombardment mass spectrometry - pMBHA 4-methylbenzhydrylamine - TFA trifluoroacetic acid This paper is based on a presentation given at the Symposium on Peptide Structure and Design as part of the 31st Annual ACS Western Regional Meeting held in San Diego, CA, USA, October 18–21, 1995.     

Selective dimerization of cysteines in glycopeptides and phosphopeptides

Summary To study the influence of phosphorylation and oxidation on the repeat domains of human Tau protein, we faced the challenge to selectively dimerize two cysteine-containing peptides in the presence of a nearby phosphate group. To this end, we were able to demonstrate the utility of a selective dimerization approach by forming disulfide bonds in unprotected phosphopeptides and extended the methodology to unprotected glycopeptides. Activation of one cysteine of a peptide chain with 2,2-dithiodipyridine and coupling this thiopyridyl-peptide to another peptide chain, containing an unprotected cysteine residue, yielded the mixed dimers in high purities and reasonable yields. Phosphate or sugar side chains on either peptide component remained unaffected during the activation and dimerization processes. While for mixed dimers the activated peptides were isolated by chromatography, homodimers were obtained by a simple one-pot reaction after 1 h. We demonstrate that cysteines can be dimerized in unprotected phosphopeptides and glycopeptides, without any side reactions affecting these posttranslational modifications.Abbreviations DCM dichloromethane - DMF N,N-dimethylformamide - DTP 2,2-dithiodipyridine - Fmoc 9-fluorenylmethyloxycarbonyl - HPLC high-performance liquid chromatography - MALDI matrix-assisted laser desorption/ionization - MS mass spectrometry - NFT neurofibrillary tangles - PHF paired helical filaments - PKC protein kinase C - RP reversed phase - human Tau protein - TFA trifluoroacetic acid Parts of this paper were presented at the 24th European Peptide Symposium in Edinburgh, Scotland, U.K., September 8–13, 1996.     

Immobilization studies of whole microbial cells on transition metal activated inorganic supports

Summary Whole cells of Saccharomyces bayanus, Saccharomyces cerevisiae and Zymomonas mobilis were immobilized by chelation/metal-link processes onto porous inorganic carriers. The immobilized yeast cells displayed much higher sucrose hydrolyzing activities (90–517 U/g) than the bacterial, Z. mobilis, cells (0.76–1.65 U/g). The yeast cells chelated on hydrous metal oxide derivative of pumice stone presented higher initial -d-fructofuranosidase (invertase, EC 3.2.1.26) activity (161–517 U/g) than on other derivatives (90–201 U/g). The introduction of an organic bridge between the cells and the metal activator led to a decrease of the initial activity of the immobilized cells, however S. cerevisiae cells immobilized on the carbonyl derivative of titanium (IV) activated pumice stone, by covalent linkage, displayed a very stable behaviour, which in continuous operation at 30° C show only a slightly decrease on invertase activity for a two month period (half-life=470 days). The continuous hydrolysis of a 2% w/v sucrose solution at 30° C in an immobilized S. cerevisiae packed bed reactor was described by a simple kinetic model developed by the authors (Cabral et al., 1984a), which can also be used to predict the enzyme activity of the immobilized cells from conversion degree data.     

Interaction of horse cytochromec with the photosynthetic reaction center ofRhodospirillum rubrum

Mitochondrial cytochromec (horse), which is a very efficient electron donor to bacterial photosynthetic reaction centersin vitro, binds to the reaction center ofRhodospirillum rubrum with an approximate dissociation constant of 0.3–0.5 µM at pH 8.2 and low ionic strength. The binding site for the reaction center is on the frontside of cytochromec which is the side with the exposed heme edge, as revealed by differential chemical acetylation of lysines of free and reaction-center-bound cytochromec. In contrast, bacterial cytochromec ₂ was found previously to bind to the detergent-solubilized reaction center through its backside, i.e., the side opposite to the heme cleft [Rieder, R., Wiemken, V., Bachofen, R., and Bosshard, H. R. (1985).Biochem. Biophys. Res. Commun. 128, 120–126]. Binding of mitochondrial cytochromec but not of mitochondrial cytochromec ₂ is strongly inhibited by low concentrations of poly-l-lysine. The results are difficult to reconcile with the existence of an electron transfer site on the backside of cytochromec ₂.     

Mykologische Studien

Ohne ZusammenfassungMykol. Studien I–X mit insges. 158 Seiten, 12 Tafeln und 35 Textabb.:I. Ein Experiment mitPhallus, Archiv f. Protistenkunde, Bd. 64, 1928, S. 1–18, 1 Tafel.II.Geaster triplex, ebenda, Bd. 65, 1929, S. 65–77, 8 Textabb.III.Xanthochrous cuticularis, ebenda, Bd. 65, 1929, S. 321–329, 5Textabb.IV. Zur Entwicklungsgeschichte vonMutinus caninus, ebenda, Bd. 72, 1930, S. 214–246, 2 Tafeln.V. ZuXanthochrous cuticularis undXanth. hispidus, ebenda, Bd. 72, 1930, S. 420–432, 4 Tafeln, 3 Textabb.VI.Spongipellis Litschaueri (=Polyporus Schulzeri Fr. sensuBresadola), ebenda, Bd. 75, 1931, S. 297–314, 2 Tafeln, 2 Textabb.VII.Mycenastrum corium, ein für Deutscheuropa neuer Gastromycet, ebenda, Bd. 78, 1932, S. 473–494, 7 Textabb.VIII.Bovista echinella undLycoperdon velatum, Beihefte z. Bot. Centralbl., Bd. 51, 1933, Abt. I, S. 269–286, l Tafel, 4 Textabb.IX. Über die Fruchtkörperentwicklung der Geastraceen, ebenda, Bd. 52, 1934, Abt. A, S. 269–289, 1 Tafel, 6 Textabb.X.Pleurotus calyptratus Fr., Biologia generalis, Bd. 10, 1934, S. 457–368, 1 Tafel.     

l-NNA inhibits the histochemical NADPH-d reaction in rat spinal cord neurons

In nerve tissue the histochemical nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) reaction is considered a suitable marker for nitric oxide synthase (NOS) activity. We have previously shown that the NOS-specific inhibitorl-nitroarginine (l-NNA) can block NADPH-d staining in intermediolateral (IML) neurons of the rat spinal cord; such a reaction might serve as a control for the presence of a NOS-related catalytic activity, i.e.,l-NNA-dependent NO synthesis in these neurons. However,l-NNA inhibition of neuronal NADPH-d is inconsistent and is therefore disputed by others. This prompted us to reinvestigate the reaction conditions to provide a standardized protocol for inhibition experiments. In IML neurons of formaldehyde-fixed spinal cord tissue, inhibition of NADPH-d reaction was tested by preincubation of frozen sections with the flavin-binder diphenylene iodonium chloride (DPI, 10 M-1 mM) which blocked the NADPH-d reaction in a concentration-dependent way, suggesting an inverse relationship of inhibitor concentration and final reaction product generated. Preincubation with the NOS-specific inhibitorl-NNA in glycine-NaOH buffer (pH 8.5–9.5) but notl-nitroarginine methyl ester (l-NAME) revealed a concentration-dependent blocking effect on neuronal NADPH-d comparable to the effects seen with DPI, suggesting the existence of al-NNA sensitive NADPH-d activity. Blocking withl-NNA (100 M-10 mM) was prevented by excessl-arginine (10–100 mM), suggesting competitive binding sites. NADPH-d staining was not inhibited by 7-nitro indazole, another NOS inhibitor. Thus, in formaldehyde-fixed nervous tissue both DPI andl-NNA inhibit the NOS-associated catalytic NADPH-d activity, thereby preventing NADPH-dependent conversion of nitroblue tetrazolium to formazan.Presented in the Workshop Detection of NO-synthases at the XXXVI Symposium of the Society for Histochemistry on Oxy Radicals, 20–23 September 1994, Heidelberg, Germany     

The mantle, ink sac, ink, arm hooks and soft body debris associated with the shells in Late Triassic coleoid cephalopod Phragmoteuthis from the Austrian Alps

Fragmentarily preserved shells – mainly pro-ostraca, in several cases also phragmocones – occurring together with arm hooks and the ink sac of the Carnian (Late Triassic) coleoid cephalopod Phragmoteuthis bisinuata (Bronn) from Lunz (Austria) are examined with the scanning electron microscope and energy-dispersive spectrometer. The pro-ostracum bears black, shiny, pitch-like sheets. The black sheets, the ink sac content and the arm hooks have a granular ultrastructure of 0.1–1 μm grain size. The arm hooks and black sheets are micro-laminated; each lamina consists of fibres. The ink consists of an agglomerate of grains. On the ventral (internal) side of the pro-ostracum, the black sheets occasionally bear agglomerates of homogeneous, ink-like material along with heterogeneous structures. The pro-ostracum has crystal-shaped units with lamello-columnar ultrastructure of the inner layer and plate ultrastructure of the outer layer. This resembles the Late Triassic Lunzoteuthis [Doguzhaeva, L.A., Mutvei, H., Summesberger, H., 2005a. A Late Triassic coleoid from the Austrian Alps: the pro-ostracum viewpoint. In: Kostak, M., Marek, J. (Eds.), Proceedings of the 2nd International Symposium on Coleoid Cephalopods Through Time. Short Papers/Abstracts Vol. Prague, 26–29 September, 2005, pp. 55–59] and Early Jurassic Belemnotheutis [Doguzhaeva, L.A., Donovan, D.T., Mutvei, H., 2005b. The rostrum, conotheca and pro-ostracum in the Jurassic coleoid Belemnotheutis Pearce from Wiltshire, England. In: Kostak, M., Marek, J. (Eds.), Proceedings of the 2nd International Symposium on Coleoid Cephalopods Through Time. Short Papers/Abstracts Vol. Prague, 26–29 September, 2005, pp. 45–49]. The black sheets, the material on their inner surface, the ink and the arm hooks consist of carbon, occasionally with minor amounts of sulfur. The shell is of calcium carbonate.Based on their organic composition, position in the shell and lamello-fibrillar ultrastructure, the black sheets are considered to be remains of the mantle, sometimes with ink sac and soft body debris. The carbon composition and granular ultrastructure of arm hooks, ink, and soft tissue remains indicate that the non-mineralized structures are pseudomorphosed by carbon (carbonization), possibly due to C-accumulating bacteria.     

Zwei neue Arten der GattungSaponaria (Caryophyllaceae) aus Afghanistan und Pakistan

Saponaria stenopetala sp.n. in Eastern Afghanistan is close toS. pachyphylla Rech. f. andS. subrosularis Rech. f.—The nearest allies ofS. makranica sp.n. from Western Pakistan and Southeastern Iran areS. kermanensis Bornm. andS. floribunda (Kar. & Kir.)Boiss.

Flora Iranicae praecursores 36–37. — Praecursores praecurrentes in Pl. Syst. Evol.139, 313–317 (1982).     

Pollen morphology ofSonchus and related genera,and a general discussion

The pollen morphology of the taxa belonging to the generaAetheorhiza Cass.,Launaea Cass.,Reichardia Roth andSonchus L. in the Iberian Peninsula has been studied with light and electron microscopy. The pollen is 3(-4)-zonocolporate and echinolophate (without polar lacunae, but in general with prelacunae), with equatorial ridges and 15–20 lacunae: 3–4 poral, 6–8 abporal and 6–8 paraporal. Small to medium size, P × E = 19–36 × 23–42 µm; sometimes two different sizes have been found. Exine 3–9 µm thick and ornamentation microreticulate and echinate. The results clearly show the relationships between genera. Moreno-Socías, E., Mejías, J. A., Díez, M. J., 1994: Morfología polínica deLactuceae (Asteraceae) en la Península Ibérica, I.Lactuca y géneros relacionados. — Acta Bot. Malacitana.19: 103–113.     

Even more new taxa from South and East Anatolia II

10 new Turkish taxa are described:Arenaria eliasiana, A. sivasica, A. monscragus, A. angustifolioides; Campanula lycica; Scutellaria orientalis subsp.tortumensis; Stachys choruhensis, S. tundjeliensis; Calamintha caroli-henricana; Aristolochia rechingeriana, the latter two species named in honour ofKarl Heinz Rechinger;Allium vuralii. Dedicated to Prof. DrKarl Heinz Rechinger on the occasion of his 80th birthday. For part I see Pl. Syst. Evol.154, 111–128.     

Saggio di inoculazioni incrociate di funghi patogeni tra animali e piante

Summary Common frogs (Rana edulis) were inoculated intraperitoneally with the following fungi: 1) pathogenic for man and animals:Coccidioides immitis, Gilchristia dermatitidis, Paracoccidioides brasiliensis, Phialophora verrucosa andSporotrichum beurmanni; 2) pathogenic for man and plants:Sporotrichum poae; 3) pathogenic for plants:Botrytis cinerea. The fungi of the group 1) (and, to a lesser extent, the group 2) produced a localized granuloma, without (or almost without) dissemination, with a reduced, aspecific reaction, chiefly in the gastro-duodenal plica. The species of the group 3) is not pathogenic at all.On the contrary, for broad bean young plants (and, to a lesser extent, castor bean plants) the fungi of the group 1) were not pathogenic, while the fungus of the group 3) was fully pathogenic.S. poae appears to be of moderate pathogenicity; less pathogenic has beenS. beurmanni.

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Un riassunto parziale di queste prove è stato presentato dai due Autori al Third International Congress for Microbiology, New York, 2–9 September 1939 (Sect. VI, Paper No. 5) e pubblicato nel 1940 (Redaelli P., Ciferri R. eBaldacci Blastomycosis, Sporotrichosis and Coccidioidal granuloma on animals and plants. Mycopathologia,II, 322–326 1940. Le esperienze furono quindi proseguite dai due Autori seniores, secondo una più vasta scala di ricerche, sinchè il sopraggiungere della guerra e le difficoltà di lavoro inerenti obbligarono a sospenderle. Ancora nell'intento di onorare la memoria del compianto amico e collaboratore Prof.P. Redaelli, ci decidiamo a dare alla luce queste note, ora pubblicate in esteso, completate con le prove eseguite dopo la presentazione della nota suddetta. R. C.     

Biochemical properties of yeast l-asparaginase

Only a single l-asparaginase has been found in the yeast Saccharomyces cerevisiae. The enzyme is synthesized constitutively, and its functioning is not controlled by the products of its activity. The apparent K_m for the yeast l-asparaginase reaction is 2.5×10^–4 m. Activity is greatest at pH 8.5 and is unaffected by the ionic strength of reaction mixtures. l-Asparagine can serve as the sole nitrogen source for cell metabolism but cannot serve as the sole supply of carbon. Active l-asparaginase is necessary for the use of l-asparagine as a nitrogen donor for cell growth. This requirement suggests a possible way in which l-asparaginase-deficient strains of yeast or other organisms might easily be selected.G.E.J. was supported by U.S. Public Health Service Predoctoral Fellowship No. 5 F01 GM36,437.     

Histochemical demonstration of carbonic anhydrase activity

Summary Freeze-dried frozen sections are floated on the surface of the freshly prepared incubation mixture (CoSO₄ 1.75 × 10^–3 M, H₂SO₄ 5.3 × 10^–2 M, NaHCO₃ 1.57 × 10^–2 M and KH₂PO₄ 1.17 to 11.7 × 10^–3 M; demonstration of weak activity requires high phosphate). A compound containing cobalt and phosphorous precipitates at carbonic anhydrase sites and is converted to CoS. Adequate staining requires only 2–10 minutes of incubation. Actazolamide inhibits the staining reaction in specific concentrations. Actazolamidein vivo, 20 mg/kgi.v. to mice 30 minutes before sacrifice also inhibited the staining. The proportion phosphorous in the specific precipitate increases with KH₂PO₄ of the medium (shown by the addition of⁶⁰Co and³²P). An explanation of the reaction mechanism is given, based on the catalyzed loss of CO₂ in the surface layer. The inclusion of phosphate in the medium makes this modification ofHäusler's method so sensitive that it shows carbonic anhydrase activity in for instance stratum spinosum of the skin.This investigation was supported by grants from the Medical Faculty, University of Uppsala and from the U.S. National Institutes of Health (Grant NB 3060 to E.Bárány).     

Production and initial characterisation of the xylan-degrading system of Phanerochaete chrysosporium

We report the optimum conditions for the degradation of oat spelt arabinoxylan and a preliminary characterisation of the inducible xylan-degrading system of the lignin-degrading white-rot fungus Phanerochaete chrysosporium. Xylanase activity was optimal at pH 5.0 and 50°C; see attached sheet the maximum reaction velocity (V_max) of the system was 3.86 units (U) mg^–1 protein with arabinoxylan as substrate and the substrate concentration giving half V_max (S_0.5) was 0.52 mg ml^–1. At concentrations of arabinoxylan greater than 15 mg ml^–1 excess substrate inhibition was observed. Xylose at 0.9 mm inhibited activity to the extent of 50%. Xylanase activity increased as a function of the dilution of the enzyme preparation prior to assay. It was resolved into four peaks by using a DEAE-Biogel column; the material in these peaks differed with respect to xylan solubilisation and the formation of reducing sugars. Electrofocusing gels allowed visualisation of several bands of activity corresponding to each peak. The arabinoxylan degradation system of P. chrysosporium is therefore composed of multiple components. Correspondence to: P. Broda     

A Novel and Simple Method for the Purification of Extracellular Levansucrase from <Emphasis Type="Italic">Zymomonas mobilis</Emphasis>

A new and simple method for the purification of extracellular levansucrase from Zymomonas mobilis from highly viscous fermentation broth was developed. After incubation of the fermentation broth with a fructose-polymer cleaving enzyme preparation (Fructozyme, Novozymes, DK) for 48 h, levansucrase precipitated as aggregates and was redissolved in a 3 M urea solution. By ongoing size-exclusion chromatography on Sephacryl S-300 the final levansucrase preparation was purified 100-fold and exhibited a specific activity of 25–35 U/mg_protein. The levansucrase was stable in 3 M urea solution for at least four months without inactivation. To maximize the enzyme yield the dynamic changes of extracellular levansucrase activity during fermentation were investigated. The highest levansucrase activity was observed during the logarithmic phase of growth (15–19 h of fermentation).Received: 26 September 2002 / Accepted: 24 October 2002     

Studies on the biology of some freshwater fishes Part VI. Mystus cavasius (Ham.)

Summary The biology of a freshwater fish, M. cavasius with particular reference to its length frequency, breeding and food has been described. length frequency distribution gave an indication of 4 modes during the quarter, July–September.Both the sexes attain maturity when they are approximately 10 cm long. Females grow larger than the males and are more abundant in the population. The spawning of this fish seems to take place during August and September. Maturing ovaries of females show only one batch of eggs which is probably shed in a single spawning act. The condition factor of the fish has no correlation either with the seasonal changes in maturity or with the feeding rhythm. The fish has an omnivorous habit and consumes all types of food available in the habitat. The feeding is high during the monsoon and winter months and low during the summer months.This work was carried out in the Department of Zoology, Aligarh Muslim University, Aligarh, U.P. India in continuation of the series I–III by Qasim & Qasim (1964) and IV–V published elsewhere by the present author (1970–71).     

Restriction/modification in Streptococcus thermophilus: isolation and characterization of a type II restriction endonuclease Sth455I

Streptococcus thermophilus strain CNRZ 455 produces a type II restriction endonuclease designated Sth455I. This enzyme was isolated from cell extracts by anionic and cationic exchange chromatography. This yielded an enzyme preparation free of non-specific nucleases. The optimal reaction conditions for Sth455I are: MgCL₂, 30 mm; pH range, 8–9; incubation temperature, 37–42°C; and a high NaCl concentration, 100–200 mm. The results of single- and double-digestion experiments indicates that Sth455I is an isoschizomer of BstNI and EcoRII showing different sensitivity to methylation. The enzyme exhibits restriction activity on the DNA of three bacteriophages of S. thermophilus and no activity on the phage lytic for strain CNRZ 455. The restriction/modification system associated with this strain is discussed.