Osteoclast formation from mononuclear phagocytes: role of bone-forming cells

In a previous study, using co-cultures of embryonic bone rudiments stripped of periosteum, and mononuclear phagocytes of various sources, we found that multinucleated mineral-resorbing osteoclasts developed in vitro from radiosensitive mouse bone marrow mononuclear phagocytes (BMMP). (Burger, E. H., J. W. M. van der Meer, J. S. van de Gevel, C. W. Thesingh, and R. van Furth, 1982, J. Exp. Med. 156:1604-1614). In the present study, this co-culture technique was used to analyze the influence of bone-forming cells on osteoclast formation and bone resorption by BMMP or peritoneal exudate cells (PEC). BMMP or PEC were co-cultured with liver or dead bone, i.e., in the presence or absence of liver bone-forming cells. Mineral resorption and osteoclast formation were monitored via 45Ca release from prelabeled live or dead bone followed by histology. Osteoclasts developed from precultured BMMP as indicated by [3H]thymidine labeling, but only in live and not in dead bone. They formed readily from BMMP but only erratically, and after a longer culture period, from PEC. Macrophages from BMMP and PEC invaded live and dead bone rudiments but did not resorb the intact mineralized matrix. In contrast, ground bone powder was resorbed avidly by both cell populations, without formation of osteoclasts. We conclude that live bone-forming cells are required for osteoclast formation from progenitors. Live bone is only resorbed by osteoclasts, and not by macrophages. Osteoclast progenitors are abundant in cultures of BMMP but scarce in PEC, which makes a direct descendance of osteoclasts from mature macrophages unlikely.     

安徽植物补遗（一）

报道《安徽植物志》未记载的１８种地理分布新记录植物,分隶于１５科,１８属,全部标本均存于安徽师范大学生物系植物标本室。     

Book Reviews

Book Reviewed in this article:
DFG-ökotoxikologie von Pflanzenschutzmitteln-Mitteilungen I, 1994
Bennett, W. F. (ed) .
Arit, K. Enzian, S. and Pallut, B.
Ettl, H., G. Gärtner .
Blume, H.-P., Felix-Henningsen, P., Fischer, W. R., Frede, H.- G., Horn, R., Stahr, K.
Mielke, H.
Goodman, R.N., Novacky, A.J.
Karg, W., Freier, B.
Müller, R. et al .
Landsmann, J., Casper, R.
Shigo, A. L.
P etrini , O. and G. B. O uelletre (eds), Host Wall Alterations by Parasitic Fungi .     

XXXII.—Some Spring Observations on the Birds of the Camargue.

T he present communication embodies the combined observations of the authors on several spring visits to the Camargue. W. B. A. paid a visit in March 1905, and another, in company with Mr. H. M. Wallis, M.B.O.U., from 26 April to 2 May, 1928. T. H. H. spent from 13 to 18 April, 1931, in the area. W. B. A., H. J. R. P., and B. W. T. made a joint expedition from 9 to 13 April, 1932, and H. J. R. P. remained on until 28 April.     

BUCHBESPRECHUNGEN

T uck , G. S.; H einzel , H.: Die Meeresvögel der Welt. Ein Taschenbuch für Ornithologen und Naturf reunde. Aus dem Englischen übers. u. bearb. von E lisabeth und Dr. H. G oethe
K nussmann , R.: Vergleichende Biologie des Menschen
K aestner , A. (Begründer): Lehrbuch der speziellen Zoologie. Band I: Wirbellose Tiere. Herausgegeben von H ans -E ckhard G runer
H eberer , G.: Allgemeine Abstammungslehre. 2., neu bearb. und erweit. Aufl. von B. Z epernick
M oore , W. J.: The Mammalian Skull. Biological Structure and Function 8
R andall , D. J.; B urggren , W. W.; F arrell , A. P.; H aswell , M. S.: The evolution of air breathing in vertebrates
S auer , H. W.: Entwicklungsbiologie. Ansätze zu einer Synthese. Mit einem Geleitwort vonF. S eidel . Hochschultext
H ardisty , M. W.: Biology of the Cyclostomes. (Biologie der Cyclostomen). London: Chapman and Hall 1979. XIV, 428 S., zahlreiche Abb., graph
W eick , F.: Die Greifvögel der Welt. Ein farbiger Führer zur Bestimmung der Ordnung Fakoniformes. Unter Mitarbeit von L. H. B rown , Karen, Kenia. Hamburg und Berlin
A pfelbach , R.; D öhl , J.: Verhaltensforschung. 3., neubearb. u. erw. Aufl
H ennig , W illi : Phylogenetische Systematik. Hrsg. Prof. Dr. W olfgang H ennig
K ämpfe , L.; K ittel , R.; K lapperstück , J.: Leitfaden der Anatomie der Wirbeltiere. 4.,überarb     

A conserved tryptophan in nitric oxide synthase regulates heme-dioxy reduction by tetrahydrobiopterin.

In nitric oxide synthase (NOS), (6R)-tetrahydrobiopterin (H(4)B) binds near the heme and can reduce a heme-dioxygen intermediate (Fe(II)O(2)) during Arg hydroxylation [Wei, C.-C., Wang, Z.-Q., Wang, Q., Meade, A. L., Hemann, C., Hille, R., and Stuehr, D. J. (2001) J. Biol. Chem. 276, 315-319]. A conserved Trp engages in aromatic stacking with H(4)B, and its mutation inhibits NO synthesis. To examine how this W457 impacts H(4)B redox function, we performed single turnover reactions with the mouse inducible NOS oxygenase domain (iNOSoxy) mutants W457F and W457A. Ferrous mutants containing Arg and H(4)B were mixed with O(2)-containing buffer, and then heme spectral transitions, H(4)B radical formation, and Arg hydroxylation were followed versus time. A heme Fe(II)O(2) intermediate was observed in W457A and W457F and had normal spectral characteristics. However, its disappearance rate (6.5 s(-1) in W457F and 3.0 s(-1) in W457A) was slower than in wild-type (12.5 s(-1)). Rates of H(4)B radical formation (7.1 s(-1) in W457F and 2.7 s(-1) in W457A) matched their rates of Fe(II)O(2) disappearance, but were slower than radical formation in wild-type (13 s(-1)). The extent of H(4)B radical formation in the mutants was similar to wild-type, but their radical decayed 2-4 times faster. These kinetic changes correlated with slower and less extensive Arg hydroxylation by the mutants (wild-type > W457F > W457A). We conclude that W457 ensures a correct tempo of electron transfer from H(4)B to heme Fe(II)O(2), possibly by stabilizing the H(4)B radical. Proper control of these parameters may help maximize Arg hydroxylation and minimize uncoupled O(2) activation at the heme.     

贵州植物区系增补Ⅱ

报道了贵州种子植物地理分布新记录属2个,即獐耳细辛属Hepatica Mill.、扭柄花属Streptopus Michx..新记录种14个,即金佛铁线莲Clematis gratopsis W.T.Wang、川鄂獐耳细辛Hepatica henryi (Oliv.) Steward、网脉唐松草Thalictrum reticulatum Franch.、阴山荠Yinshania acutangula (O.E.Schulz) Y.H.Zhang、大花杠柳Periploca tsiangii D.Fang et H.Z.Ling、钻萼唇柱苣苔Chirita subulatisepala W.T.Wang、南川橐吾Ligularia nanchuanica S.W.Liu、鸢尾叶风毛菊Saussurea romuleifolia Franch.、圆叶风毛菊Saussurea rotundifolia Chen、莲座狗舌草Tephroseris changii B.Nord.、少花黄鹌菜Youngia szechuanica(Soderb.) S.Y.Hu、地杨梅Luzula campestris (L.) DC.、疏花粉条儿菜Aletris laxiflora Bur.et Franch.、小花扭柄花Streptopus parviflorus Franch..新记录变种2个,即扇叶虎耳草Saxifraga rufescens Balf.f.var.flabellifolia C.Y.Wu et J.T.Pan、空心柴胡Bupleurum longicaule Wall.ex DC.var.franchetii H.de Boiss.     

Besprechungen

Book review in this article
Eidmann, H., Lehrbuch der Entomologie, 2. Auflage, neubearbeitet von F. K ühlhorn .
Hoffmann, W., A. Mudra und W. Plarre, Lehrbuch der Züchtung landwirt-schaftlidier Kulturpflanzen.
The Actinomycetales - The Jena International Symposium on Taxonomy. Edited by H. PRAUSER.     

Buchbesprechungen/Book Reviews

Books reviews in this article:
Brouwer, W., Handbuch des Speziellen Pflanzenbaues.
Sachs, L., Angewandte Statistik, Planung und Auswertung - Metboden und Modelle.
Koepf, H. H., B. D. Pettersson und W. Schaumann, Biologiscbe Landwirtsdiaft, eine Einfiihrung in die biologisch-dynamische Wirtschaftsweise.
Nultsdi, W., Allgemeine Botanik. Kurzes Lehrbuch fiir Mediziner und Naturwissenschaftler.
MacHattie, L. B., and F. Sdinelle, An Introduction to Agrotopoclimatology.
Mitteilungen aus der Biologisdien Bundesanstalt fiir Land- und Forstwirtschaft Berlin-Dahlem, Heft 156 (1974):
Hassebrauk, K., und G. Robbelen, Der Gelbrost, Puccinia striiformis West.
Mitteilungen aus der Biologischen Bundesanstalt fur Land- und Forstwirtschaft Berlin-Dahlem, Heft 157 (1974):
Niemann, P., Untersuchungen iiber die Wirkung von Bodenherbiziden auf Immissionsstandorten im rheinischen Braunkohlenrevier.
Mitteilungen aus der Biologischen Bundesanstalt fiir Land- und Forstwirtschaft Berlin-Dahlem, Heft 158 (1974):
Zeller, W., Der Feuerbrand des Kernobstes hervorgerufen von Erwinia amylovora (Burrill) Winslow et al. (Sammelreferat).     

Different binding of human interferon alpha 1 and alpha 2 to common receptors on human and bovine cells. Studies with recombination interferons produced in Escherichia coli

Minicells from Escherichia coli DS410 harboring cDNA for human interferon (IFN) alpha 1 or alpha 2 were metabolically labeled with [3H]leucine and the radioactive IFN was purified to homogeneity by immune precipitation with anti-IFN-alpha serum. These preparations of radioactive IFN-alpha 1 and -alpha 2 were used to study the binding on two human (FL and Daudi) and one bovine (MDBK) cell lines. IFN-alpha 2 specifically bound well to both human and bovine cells, while IFN-alpha 1 bound very poorly to human cells but well to bovine cells. Specific binding of radioactive IFN-alpha 2 to these cell lines was completely inhibited by not only nonradioactive IFN-alpha 2 but also IFN-alpha 1, and binding of IFN-alpha 1 to bovine cell was also competed by IFN-alpha 2 as well as IFN-alpha 1, indicating that the receptors for both IFNs are identical. However, 50-100-fold (on human cells) or 4-fold (on bovine cell) more nonradioactive IFN-alpha 1 than -alpha 2 was required to inhibit the binding of radioactive IFN-alpha 2 to the receptors. Scatchard analysis showed that IFN-alpha 1 and -alpha 2 bind to the receptors on human cells with an apparent Kd of greater than 6 X 10(-10) and 3 X 10(-11) M, respectively, while on bovine cells with a Kd of 4.2 X 10(-11) and 1.6 X 10(-11) M, respectively. These results show that the different target cell specificity of IFN-alpha 1 and -alpha 2 in regard to antiviral activity (Streuli, M., Hall, A., Boll, W., Stewart, W. E., II, Nagata, S., and Weissmann, C. (1981) Proc. Natl. Acad. Sci. U. S. A. 78, 2848-2852) is due to the different binding activity of IFN-alpha molecules to their common receptors.     

The elasticity of synthetic phospholipid vesicles obtained by photon correlation spectroscopy

Osmotic-swelling experiments were conducted on a variety of preparations of "uniform" unilamellar vesicle systems. The synthetic lipid preparations included both vesicles produced by extrusion through polycarbonate ultrafiltration membranes and vesicles produced by the pH-adjustment method. The vesicles were monitored by photon correlation spectroscopy during swelling as the osmolarity of the external solution was decreased. Contrary to our previously reported results [Aurora, T. S., Li, W., Cummins, H. Z., & Haines, T. H. (1985) Biochim. Biophys. Acta 820, 250-258; Li, W., & Haines, T. H. (1986) Biochemistry 25, 7477-7483; Li, W., Aurora, T. S., Haines, T. H., & Cummins, H. Z. (1986) Biochemistry 25, 8220-8229; Haines, T. H., Li, W., Green, M., & Cummins, H. Z. (1987) Biochemistry 26, 5439-5447] large unilamellar vesicles produced from acidic lipids by the pH-adjustment technique were highly polydisperse and did not swell in a manner that permitted the computation of a Young's modulus, presumably due to the polydispersity. Also contrary to our previous reports, membranes derived from bovine submitochondrial particles did not produce evidence of swelling when subjected to similar protocols. Analysis of osmotic swelling of extruded unilamellar vesicles has allowed us to assign Young's moduli for bilayers of dioleoylphosphatidylcholine and dioleoylphosphatidylglycerol, in the range (5-8) x 10(8) and (3-6) x 10(8) dyn/cm2, respectively. The diameters and polydispersites obtained with electron microscopy and photon correlation spectroscopy were compared directly and with computer-modeling techniques. While excellent agreement was obtained for distributions with low polydispersity (approximately greater than 0.1), serious disagreement was found when the polydispersity exceeded approximately 0.2.     

Activation of active-site cysteine residues in the peroxiredoxin-type tryparedoxin peroxidase of Crithidia fasciculata.

Tryparedoxin peroxidase (TXNPx), recently identified as the hydroperoxide-detoxifying enzyme of trypanosomatidae [Nogoceke, E., Gommel, D. U., Kiess, M., Kalisz, H. M. & Flohé, L. (1997) Biol. Chem. 378, 827-836], is a member of the peroxiredoxin family and is characterized by two VCP motifs. Based on a consensus sequence of TXNPx and peroxiredoxin-type peroxidases, eight TXNPx variants were designed, heterologously expressed in Escherichia coli, checked for alpha-helix content by CD and kinetically analysed. The variant Q164E was fully active, C52S, W87D and R128E were inactive and C173S, W87H, W177E and W177H showed reduced activity. Wild-type TXNPx and Q164E exhibit ping-pong kinetics with infinite maximum velocities, whereas saturation kinetics were observed with C173S and W177E. The data comply with a mechanism in which C52, primarily activated by R128 and possibly by W87, is first oxidized by hydroperoxide to a sulfenic acid derivative. C173, supported by W177, then forms an intersubunit disulfide bridge with C52. If C173 is exchanged with a redox-inactive residue (Ser) or is insufficiently activated, the redox shuttle remains restricted to C52. The shift in the kinetic pattern and decrease in specific activity of C173S and W177E may result from a limited accessibility of the oxidized C52 to tryparedoxin, which in the oxidized wild-type TXNPx presumably attacks the C173 sulfur of the disulfide bridge. The proposed mechanism of action of TXNPx is consistent with that deduced for the homologous thioredoxin peroxidase of yeast [Chae, H. Z., Uhm, T. B. & Rhee, S. G. (1994) Proc. Natl Acad. Sci. USA 91, 7022-7026] and is supported by molecular modelling based on the structure of the human peroxiredoxin 'hORF6' [Choi, H.-J., Kang, S. W. Yang, C.-H., Rhee, S. G. & Ryu, S.-E. (1998) Nat. Struct. Biol. 5, 400-406].     

Besprechungen

Books reviews in this article:
Ashton, F. M., and A. S. Crafts, Mode of Action of Herbicides.
Goss, James A., Physiology of Plants and their Cells.
Ulmann, M., Analytische Kennzeichnung von Amylose und Amylopektin.
Fungal pathogenicity and the plant's response. Herausgegeben von R. J. W. B yrde und C. V. C utting .
Boerema, G. H., and Maria M. J. Dorenbosch, The Phoma and Ascochyta species described by W ollenweber and H ochapfel in their study on fruitrotting.     

News Notes

Abstract

Wyatt, John The Shining Levels: The Story of a Man Who Went Back to Nature Philadelphia and New York: J.B. Lippincott Company, 1974 209 pp., $6.95, Reviewed by Gilbert Wright

Banfield, A.F.W. The Mammals of Canada Toronto: University of Toronto Press, 1974. 438 pp., $19.95, Reviewed by Paul F. Connor.

Mai, W. F., with H. H. Lyon, Photographer Pictorial Key to Genera of Plant-Parasitic Nematodes Ithaca and London: Comstock Publishing Associates (a division of Cornell University Press), 1975, 4th ed., rev., 219 pp., $12.50 softcover, Reviewed by Victor H. Dropkin.

Bridges, William Gathering of Animals: An Unconventional History of the New York Zoological Society New York: Harper and Row, 1974 518 pp., $12.50, Reviewed by Robert Deitchman.

Palmer, E. Laurence, Revised by H. Seymour Fowler Fieldbook of Natural History, 2d rev. ed. New York: McCraw-Hill Book Company, 1975 779 pp., $14.95, Reviewed by J. P. Kennedy.

Cohen, Daniel Animal Nature: The Biology of Human Behavior New York: McGraw-Hill Book Company, 1975 144 pp., $5.72, Reviewed by Julie Ann Miller.

Muus, Bent J., Illustrated by Preben Dahlstrom; Translated by Gwynne Vevers Collins Guide to the Sea Fishes of Britain and North-Western Europe St. James's Place, London: Collins, 1975. 244 pp., $10.00, Reviewed by Robert W. Boenig.

Barbour, Roger W., and Wayne H. Davis Mammals of Kentucky (Kentucky Nature Studies: 5) Lexington: The University Press of Kentucky, 1974 322 pp., $14.95, Reviewed by Theodore W. Munch.

Brandwein, Paul F., et. al. Concepts in Science (Newton Edition) New York, Harcourt Brace Jovanovich, 1975 376 pp., Reviewed by Malcolm F. Farmer.     

Buchbesprechungen / Book Reviews

Book reviewed in this articles:
Omar, M. H. , Meteorological factors affecting the epidemiology of the cotton leaf worm and the pink boll worm.
Omar, M. H. , The economic value of agrometeorological information and advice.
Reinert, J., and M. M. Yeoman , Plant Cell and Tissue Culture.
Hassal, K. A. , The Chemistry of Pesticides; Their Metabolism, Mode of Action and Uses in Crop Protection.
Wetzel, T. , und E. Fuchs (Wiss. Redaktion), Schaderreger in der industrie-maEigen Getreideproduktion.
Dorffling, K. , Das Hormonsystem der Pflanzen.
Zentmyer, G. A. , Phytophthora cinnamomi and the diseases it causes.
Advances in Agricultural Microbiology , edited by N. S. SUBBA RAO.
Wareing, P. F. , Plant Growth Substances 1982.
Kreuter, M.-L. , Biologischer Pflanzenschutz: naturgemafie Abwehr von Schad-lingen und Krankheiten.
Schaufele, W. R., Deleplanque & Cie (Hrsg.), Schadlinge und Krankheiten der 2iickcrriibe.
Loewus, F. A., and W. Tanner , Plant Carbohydrates I.
Hoppe, W., W. Lohmann, H. Markl, H. Ziegler (Hrsg.), Biophysik.
Mace, M. E., A. A. Bell and C. H. Beckmann (eds.). Fungal Wilt Diseases of Plants.     

Bestimmung von Chloratrückstanden im Boden

Abstract

Kozubov, G. M.; Danilova, M. F.: Atlas ultrastruktury rastitel nych kletok 295 S., 142 Tafeln. Petrozavodsk: 1972. Reviewed H. M. Müller.

Fritzsch, W.; Bremer, R.: Bienengesundheitsdienst, 1. Aufl. 200 S., 62 Abb. Jena: VEB Gustav Fischer, 1975. Reviewed W. Lehmann.

Schumakow, I. M.; Fedorintschik, N. S.; Gussew, G. W.: Biologische Pflanzenschutzimittel. 205 S., 13 Abb., Berlin, VEB Dt. Landwirtschaftsverl., 1976. Reviewed Th. Wetzel

Grimstone, A. V.; Skaer, R. J.: A guidebook to microscopical methods 134 S., 3 Abb. London: Cambridge Univ. Press, 1972. Reviewed H. M. Müller.     

BOOK REVIEWS

Bruce-Chwatt, L. J., ed., with Black, R. H., Canfield, C. J., Clyde, D. F., Peters, W. & Wernsdorfer, W. H. 1986. Chemotherapy of Malaria .
Peters, W. & Killick-Kendrick, R., eds. 1987. The Leishmaniases in Biology and Medicine , Vol. I: Biology and Epidemiology
Euzéby, Jacques. 1987. Protozoologie Médicate Comparée. Les Protozooses des Animaux et Leurs Relations Avec les Protozooses de l'Homme , Vol. II: Myxozoa—Microspora—Ascetospora. Apicomplexa, 1: Coccidioses (Sensu Lato ).
McDougald, L. R., Joyner, L. P. & Long, P. L., eds. 1986. Research in Avian Coccidiosis .
Wichterman, R. 1986. The Biology of Paramecium, 2nd ed.
Levine, N. D. & Ivens, V. 1986. The Coccidian Parasites (Protozoa, Apicomplexa) of Artiodactyla .     

A conserved tryptophan 457 modulates the kinetics and extent of N-hydroxy-L-arginine oxidation by inducible nitric-oxide synthase

In the oxygenase domain of mouse inducible nitric-oxide synthase (iNOSoxy), a conserved tryptophan residue, Trp-457, regulates the kinetics and extent of l-Arg oxidation to N(omega)-hydroxy-l-arginine (NOHA) by controlling electron transfer between bound (6R)-tetrahydrobiopterin (H(4)B) cofactor and the enzyme heme Fe(II)O(2) intermediate (Wang, Z. Q., Wei, C. C., Ghosh, S., Meade, A. L., Hemann, C., Hille, R., and Stuehr, D. J. (2001) Biochemistry 40, 12819-12825). To investigate whether NOHA oxidation to citrulline and nitric oxide (NO) is regulated by a similar mechanism, we performed single turnover reactions with wild type iNOSoxy and mutants W457F and W457A. Ferrous proteins containing NOHA plus H(4)B or NOHA plus 7,8-dihydrobiopterin (H(2)B), were mixed with O(2)-containing buffer, and then heme spectral transitions and product formation were followed versus time. All three proteins formed a Fe(II)O(2) intermediate with identical spectral characteristics. In wild type, H(4)B increased the disappearance rate of the Fe(II)O(2) intermediate relative to H(2)B, and its disappearance was coupled to the formation of a Fe(III)NO immediate product prior to formation of ferric enzyme. In W457F and W457A, the disappearance rate of the Fe(II)O(2) intermediate was slower than in wild type and took place without detectable build-up of the heme Fe(III)NO immediate product. Rates of Fe(II)O(2) disappearance correlated with rates of citrulline formation in all three proteins, and reactions containing H(4)B formed 1.0, 0.54, and 0.38 citrulline/heme in wild type, W457F, and W457A iNOSoxy, respectively. Thus, Trp-457 modulates the kinetics of NOHA oxidation by iNOSoxy, and this is important for determining the extent of citrulline and NO formation. Our findings support a redox role for H(4)B during NOHA oxidation to NO by iNOSoxy.     

Book Reviews

Book reviewed in this article:
Kegler, H. und W. Friedt (Hrsg.) , Resistenz von Kulturpflanzen gegen pflanzenpathogene Viren.
Kees, H., E. Beer, H. Bötger, W. Garburg, G. Meinert und E. Meyer , Unkrautbekämpfung im Integrierte Pflanzenschutz: Ackerbau, Feldgemüse, Grünland.     

Functional effects of periodic tryptophan substitutions in the alpha M4 transmembrane domain of the Torpedo californica nicotinic acetylcholine receptor

Previous amino acid substitutions at the M4 domain of the Torpedo californica and mouse acetylcholine receptor suggested that the location of the substitution relative to the membrane-lipid interface and perhaps to the ion pore can be critical to the channel gating mechanism [Lasalde, J. A., Tamamizu, S., Butler, D. H., Vibat, C. R. T., Hung, B., and McNamee, M. G. (1996) Biochemistry 35, 14139-14148; Ortiz-Miranda, S. I., Lasalde, J. A., Pappone, P. A., and McNamee, M. G. (1997) J. Membr. Biol. 158, 17-30; Tamamizu, S., Lee, Y. H., Hung, B., McNamee, M. G., and Lasalde-Dominicci, J. A. (1999) J. Membr. Biol. 170, 157-164]. In this study, we introduce tryptophan substitutions at 12 positions (C412W, M415W, L416W, I417W, C418W, I419W, I420W, G421W, T422W, V423W, S424W, and V425W) along this postulated lipid-exposed segment M4 so that we can examine functional consequences on channel gating. The expression levels of mutants C412W, G421W, S424W, and V425W were almost the same as that of the wild type, whereas other mutants (M415W, L416W, C418W, I419W, I420W, T422W, and V423W) had relatively lower expression levels compared to that of the wild type as measured by iodinated alpha-bungarotoxin binding ([(125)I]-alpha-BgTx). Two positions (L416W and I419W) had less than 20% of the wild type expression level. I417W gave no detectable [(125)I]BgTx binding on the surface of oocyte, suggesting that this position might be involved in the AChR assembly, oligomerization, or transport to the cell membrane. The alphaV425W mutant exhibited a significant increase in the open channel probability with a moderate increase in the macroscopic response at higher ACh concentrations very likely due to channel block. The periodicity for the alteration of receptor assembly and ion channel function seems to favor a potential alpha-helical structure. Mutants that have lower levels of expression are clustered on one side of the postulated alpha-helical structure. Mutations that display normal expression and functional activity have been shown previously to face the membrane lipids by independent labeling studies. The functional analysis of these mutations will be presented and discussed in terms of possible structural models.