Charles Darwin's theory of evolution: A review of our present understanding

The paper characterizes Darwin's theory, providing a synthesis of recent historical investigations in this area. Darwin's reading of Malthus led him to appreciate the importance of population pressures, and subsequently of natural selection, with the help of the wedge metaphor. But, in itself, natural selection did not furnish an adequate account of the origin of species, for which a principle of divergence was needed. Initially, Darwin attributed this to geographical isolation, but later, following his work on barnacles which underscored the significance of variation, and arising from his work on botanical arithmetic, he supposed that diversity allowed more places to be occupied in a given region. So isolation was not regarded as essential. Large regions with intense competition, and with ample variation spread by blending, would facilitate speciation. The notion of place was different from niche, and it is questioned whether Darwin's views on ecology were as modern as is commonly supposed. Two notions of struggle are found in Darwin's theory; and three notions of variation. Criticisms of his theory led him to emphasize the importance of variation over a range of forms. Hence the theory was populational rather than typological. The theory required a Lamarckian notion of inheritable changes initiated by the environment as a source of variation. Also, Darwin deployed a use/habit theory; and the notion of sexual selection. Selection normally acted at the level of the individual, though kin selection was possible. Group selection was hinted at for man. Darwin's thinking (and also the exposition of his theory) was generally guided by the domestic-organism analogy, which satisfied his methodological requirement of a vera causa principle.     

God and natural selection: The Darwinian idea of design

Conclusion If we arrange in chronological order the various statements Darwin made about God, creation, design, plan, law, and so forth, that I have discussed, there emerges a picture of a consistent development in Darwin's religious views from the orthodoxy of his youth to the agnosticism of his later years. Numerous sources attest that at the beginning of the Beagle voyage Darwin was more or less orthodox in religion and science alike.⁷⁸ After he became a transmutationist early in 1837, he concluded that the doctrine of secondary causes must be extented even to the history of life and that after the first forms of life were created, there was no further need for divine intervention, except where man was concerned. Man's body, he thought, was produced by the process of transmutation, but he believed for a time that man's soul was superadded. By mid-1838 he had become convinced that nothing, after the creation of life, was due to miracles. God works only through laws, which are capable of producing every effect of evey kind which surrounds us. The existence of man, the idea of God in man's mind, and the harmony of the whole system were in his eyes prearranged goals of deterministic laws imposed by God. Such a conception excludes the miracles on which Christianity depends; but it is not possible to say whether Darwin's loss of Christian faith, which occurred at about this same time, preceded and made possible his materialism or was rather caused or hastened by it.⁷⁹ In the weeks after his reading of Malthus, Darwin's belief in a plan of creation gave way to the belief that God created matter and life and designed their laws, leaving the details, however, to the workings of chance. This remained his view until the 1860s.There is no exact parallel between this development of Darwin's religious views and the development of his ideas on evolution, but there is a general correspondence. When he believed in a plan of creation, Darwin's theory of transmutation did not depend on struggle or the selection of chance variations. Adaptation was, for him, an automatic response to environmental chance. From late 1838 to 1859 he believed in designed laws and chance, and this belief, too, has its parallel in his theory. The element of chance in natural selection meant that there could be no detailed plan,in which even man's idea of God would be a necessary outcome of nature's laws (man himself is not a necessary outcome of the working of natural selection).⁸⁰ But Darwin still believed nature was programmed to achieve certain general ends. We might say that he believed in a general, though not a special, teleology. Natural selection was for him a law to maximize utility, creating useful organs, retaining vestiges for future use. For many years it was a law designed to produce organisms perfectly adapted to their environments. Only later did Darwin come to doubt even this sort of design in nature.⁸¹ One way of describing the development of Darwin's evolutionary thought is to say that it shows a gradual abandoning of his theistic assumptions, so that by the late 1860s his theory was informed to a slighter extent by notions of purpose and design than it was in 1838 or 1844 or 1859.     

God's magnificent law: The bad influence of theistic metaphysics on Darwin's estimation of natural selection

Conclusion It is natural for us — living after the Darwinian Revolution and the neo-Darwinian synthesis — to consider the adoption of evolution by natural selection as unconditionally rational, because it now seems the best theory or explanation of many phenomena. Nonetheless, if we take historical inquiry seriously, as allowing us to probe into the ground of our knowledge, the roots of even this rational Darwinism might be unearthed. Darwinian doctrine betrays a deceptive desire for unity and simplicity of principle, and belief that the mechanistic aspect of nature is of the highest significance. Such crucial but questionable presuppositions are more easily discerned historically, insofar as they chronologically preceded Darwin's particular theoretical conviction and were even set off as a metaphysics of divine law.We have seen how Darwin's teaching about nature emerged within that theistic metaphysics. It emerged in a prior metaphysical debate in his mind between the contemporary belief in special creations and the belief in a designed hierarchy of physical laws. One can hardly deny that Darwin favored the superior side in this contest; but the contest was a narrow one whose basic premises he never clearly criticized. On the one hand, of course, his conviction about a lawful genesis inspired him to take a broad view of things and to seek out important general phenomena. But, on the other hand, it ensured that his new empirical notions would be easily drawn into the preferred cosmology. Historically, this seems to have occurred in Darwin's adoption of Malthus' principle of population and his extension of it to the whole account of descent: Malthusianism was readily attached to an ultimate scheme of things. Consequently, the key concepts that Darwin developed out of his Malthusian views — perfect adaptation and selection — reflect his cosmological prepossession, his desire to express a total and teleological process of creation. Perhaps our most valuable, and most undervalued, token of Darwin's metaphysical orientation is his reliance on a human technique (selective breeding) to explain Nature's way. In sum, to understand Darwin's faith in his grand view of life, we should not ignore the metaphysics that preceded and structured it, the metaphysics that linked the principles of contemporary science to primordial creation. Nor should we fail to see that such a metaphysics leads natural philosophy into a shadowy realm, where system can come to look like science, and one insight like an absolute.     

Robert E. Grant: The social predicament of a pre-Darwinian transmutationist

Conclusion Wakley in 1846 called Grant at once the most eloquent, the most accomplished, the most self-sacrificing, and the most unrewarded man in the profession.¹²⁸ I have shown some of the reasons why this was so, and I have suggested that his Lamarckism was one of a number of factors that served to alienate him from the conservative scientific community in the 1830's and 1840's. I have further shown the need for a fundamental rethinking of Grant's position in the history of biology. There is little profit in seeing him as a precursor of Darwin. His importance lies as a teacher of philosophical anatomy and as the disseminator of Geoffroy's views in London. With the recent interest of historians in the emergence of a non-Paleyite approach to design in the 1830's (that is, an approach stemming from a unity of plan), a reassessment of Grant along these lines seems in order.Also, by understanding Grant's professional and transmutational threat, we can more fully appreciate the anti-Lamarckian ploys of leading scientists like Owen and Lyell. These scientific and social tactics reinforced the isolation Grant suffered as a result of his radical, materialistic, and antimonopolist views. Together with the laissez-faire arrangements at the joint-stock university, they led to his financial collapse — and to the decline of his scientific output that Darwin found so inexplicable. Beddoe described Grant as a disappointed man. Alas! wrote Wakley. Who would be an English Cuvier?¹²⁹     

Epigenetic Processes, when Natura Non Facit Saltum Becomes a Myth, and Alternative Ontogenies a Mechanism of Evolution

When I started the journal Environmental Biology of Fishes more than 25 years ago, it was designed to avoid any prejudices and scientific dogmas, to keep an open mind, and to allow publication of ideas that are irritating to followers of the so-called mainstream, ideas that few other journals dared to touch (Balon 1976, 1989d). While such articles in the journal were often ignored by the mainstream practitioners and the political establishment, none was ever opposed or proven wrong. As in many similar cases before, only time will show if these contributions were valid and of value to the advancement of knowledge.I have often wondered why it takes so long for some of the universal facts and ideas to be accepted or even to be known. I have come to believe that like with many textbooks some facts and conclusions are copied from one book to the next (as in the case of the origin of the common carp – Balon 1974, 1995a,b) without knowing or admitting that in the meantime new facts require new syntheses and conclusions. Even good scholars resist unknown facts or ideas. It is irritating that one's knowledge is inadequate or that others beat us to be first. I have wondered why wrong ideas persist for so long; but Bateson (1979, p. 206) already explained it to his daughter ... yes, your image of evolution is exact. And what Darwin called natural selection is the surfacing of the tautology or presupposition that what stays true longer does indeed stay true longer than what stays true not so long.After all it was Jean Baptiste Lamarckgrave, the founder of evolutionary theory, miserable, old, and blind, ... (Bateson 1972, p. xii) and/or Gottfried Treviranus who presented the truth long before the privileged Charles Darwin, alas in wrong languages. Over time, ignoring the truth became fashionable and the question which of the four theories of evolution (Løvtrup 1982) can be attributed to Darwin, if any, irrelevant. It is [exclaims Croizat 1977, transl. 1987, p. 137] a gross, very grave mistake to confuse Darwin as a historical figure with Darwin as an exalted figure of the thinking of biology (Croizat's italics).Nearly 30 years ago a BBC TV series and book on evolution glorified Darwin and molecular biology. Calder (1973, p. 9), the author of this book entitled The life game: evolution and the new biology felt that Darwin would [merely] need to know about the survival of the quickest, when it came to crossing the street. But the street was never crossed! Many TV viewers of the recent PBS series Evolution were again misled into believing that evolution was discovered by Darwin. Even Gould (2001) in the Introduction and the producer Hutton (2001) in the Foreword to the companion book of this series (Zimmer 2001) give the Darwinian evolution [sic] an exposé it hardly deserves. While such views have been repeatedly proven wrong, most scholars, with the exception of a few scientists, philosophers, and journalists, comfortably assume Darwin's priority in spite of numerous published evidences to the contrary. This myth is then fed to the general public. The following retrospective essay attempts to compile proofs in support of the evolutionary processes other than Darwin's natural selection and the gene-centric new synthesis, old by now as it is.     

Darwin's language may seem teleological,but his thinking is another matter

Darwin's biology was teleological only if the term teleology is defined in a manner that fails to recognize his contribution to the metaphysics and epistemology of modern science. His use of teleological metaphors in a strictly teleonomic context is irrelevant to the meaning of his discourse. The myth of Darwin's alleged teleology is partly due to misinterpretations of discussions about whether morphology should be a purely formal science. Merely rejecting such notions as special creation and vitalism does not prevent the pernicious effects of teleological reasoning, even at the present time.     

Moral commitment without objectivity or illusion: Comments on Ruse and Woolcock

Peter Woolcock, in Ruse's Darwinian Meta-Ethics: A Critique, argues that the subjectivist (nonobjectivist) Darwinian metaethics proposed by Michael Ruse (in Taking Darwin Seriously) cannot work, because the illusion of objectivity that Ruse claims is essential to morality breaks down when it is recognized as illusion, and there then remain no good reasons for acknowledging or following moral obligations. Woolcock, however, is mistaken in supposing that moral behaviour requires rational motivation. Ruse's Darwinian metaethical analysis shows why such objective support for morality is neither plausible nor necessary; and when that is recognized, it can also be seen that Ruse's proposed illusion of moral objectivity is superfluous.     

Different ζ globin gene deletions among Black Americans

Summary Four types of chromosomes with a deletion between the human embryonic and globin genes were identified among 2.8% of 321 Black Americans from Georgia. Two deletions of approximately 11 kb which differed by about 300 bp occurred on chromosomes with or without a polymorphic Xba I site 5 to the globin gene [(X⁺) or (X^-)]. The deletions are identifiable in Xba I digests of genomic DNA using an or a globin gene probe which yield fragments of 23 kb from (X⁺)–^* chromosomes or 27 kb from (X^–)–^* chromosomes. Digestion with other enzymes and probing with both and probes gave fragments typical of the two globin gene deletions previously identified in Polynesians. Among Black Americans, these globin gene deletions have been found in combination with globin gene deletions in trans but not in cis. Homozygotes have not been found. Hematologic data on carriers of the globin gene deletions in association with Hb AS, SS, and SC suggest that these deletions have no effect on the function of the adult globin genes.     

Protocol-dependence of equivalent circuit parameters of toad urinary bladder

Summary Determinations of current-voltage relationships are widely employed in the characterization of epithelial sodium transport. In order to determine the protocol dependence of transport parameters in the toad urinary bladder, studies were carried out in the presence and absence of amiloride, an inhibitor of active sodium transport. With symmetric positive and negative perturbations of the transepithelial electrical potential difference (0±100 mV) for 30 sec, the amiloride-sensitive current-voltage (i ^a -) relationship was near linear over the range –75+100 mV, indicating constancy of the conductance ^a and the apparent electromotive force E _Na, lumped parameters of the standard electrical equivalent circuit model of the active transport system. With a reverse protocol (±1000 mV) or 15 min perturbations thei ^a - relationships were highly nonlinear. Nonlinearity reflected voltage dependence of parameters: perturbations that increased active transport decreased E _Na and increased ^a, as evaluated from 10 sec perturbations of ; slowing of active transport produced the converse changes. These effects are usefully analyzed in both quasi-steady states and true steady states by means of a detailed equivalent circuit incorporating the significant ionic currents across each plasma membrane. Precise understanding of the significance of ^a and E _Na will require characterization of the partial ionic conductances on perturbation of .     

Solution conformations of proline rings in proteins studied by NMR spectroscopy

Summary Three different conformations of proline rings in a protein in solution, Up, Down and Twist, have been distinguished, and stereospecific assignments of the pyrrolidine -, - and -hydrogens have been made on the basis of ¹H-¹H vicinal coupling constant patterns and intraresidue NOEs. For all three conformations, interhydrogen distances in the pairs -³, ³-³, ²-², ²-², and ³-³ (2.3 Å) are shorter than those in the pairs -², ²-³, ³-², ²-³, and ³-² (2.7–3.0 Å), resulting in stronger NOESY cross peaks. For the Up conformation, the ³-² and ²-³ spin-spin coupling constants are small (<3 Hz), and weak cross peaks are obtained in a short-mixing-time (10 ms) TOCSY spectrum; all other vicinal coupling constants are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. For the Down form, the -², ²-³, and ³-² vicinal coupling constants are small, leading to weak TOCSY cross peaks; all other couplings again are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. In the case of a Twist conformation, dynamically averaged coupling constants are anticipated. The procedure has been applied to bovine pancreatic trypsin inhibitor and Cucurbita maxima trypsin inhibitor-V, and ring conformations of all prolines in the two proteins have been determined.     

Comparison of [35S]GTPγS binding to plasma membranes and endomembranes prepared from soybean and rat

Summary Plasma membranes were prepared from soybean hypocotyls and roots by aqueous two-phase partitioning and subsequent free-flow electrophoresis. The highly purified plasma membranes bound [³⁵S]GTPS with a relatively high affinity (K_d10nM). The binding was saturable and specific as it was indicated by the displacement of bound [³⁵S]GTPS by unlabeled GTPS and GTP, but not by ATPS, ATP, UTP or CTP. ITP was intermediate in its ability to displace [³⁵S]GTPS. When soybean plasma membrane proteins were separated by SDS-PAGE and displayed by autoradiography, two major [³⁵S]GTPS binding proteins were revealed with apparent molecular weights of 24 and 28 kDa. Results with plasma membranes from soybean hypocotyls and roots were similar but differed from those with plasma membranes prepared from rat liver and adipocytes where only a single major [³⁵S]GTPS binding activity with a molecular weight of 28 kDa was observed.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - G protein hetero-trimeric GTP binding protein with , , subunits - G_n protein GTP binding protein detected on nitrocellulose blots - GTPS guanosine 5-[-thio]triphosphate - IAA 3-indoleacetic acid - SDS-PAGE sodium dodecylsulfate-polyacrylamide gel electrophoresis     

The rise and fall of Darwin's second theory

Conclusion The difficulty of discussion between people brought up in different frameworks is to be admitted, Karl Popper writes. But nothing is more fruitful than such a discussion; than the culture clash which has stimulated some of the greatest intellectual revolutions.⁷¹ Certainly Kirby and Darwin were brought up in different cultures — Kirby with his Anglican-Tory orientation, Darwin with his Whig-liberal background — and certainly the clash generated some interesting theories; but it also resulted in the revival of Lamarck's discredited habit theory, which took another century of careful experimentation to weed out.     

The historical context of natural selection: The case of Patrick Matthew

Conclusions It should be evident from the foregoing discussion that one man's natural selection is not necessarily the same as another man's. Why should this be so? How can two theories, which both Matthew and Darwin believed to be nearly identical, be so dissimilar? Apparently, neither Matthew nor Darwin understood the other's theory. Each man's viewpoint was colored by his own intellectual background and philosophical assumptions, and each read these into the other's ideas. The words sounded the same, so they assumed the concepts must als be the same.¹²³ As Ghiselin has pointed out, historians attempting to evaluate Darwin's predecessors have been similarly blinded by a preoccupation with words, without regard to their proper context.¹²⁴ In the case of Matthew, the practice of quoting only brief passages from the appendix to Naval Timber and Arboriculture, without relating them to the rest of his work, has suggested a greater resemblance to Darwin's theory than actually exists.It is clear, both from the use which Matthew made of his ideas and from the philosophical roots of his natural world view, that he could not have arrived at the concept of natural selection by the same thought process which Darwin employed. His discussion of natural selection is presented not as an argument, but as an axiom. No theory is proposed, no evidence marshaled to support it. Natural selection is stated as a fact, a Law of Nature, unquestioned, and presumably, unquestionable.Despite his clamor for recognition as the discoverer of natural selection, Matthew recognized and acknowledged this very fundamental difference between Darwin and himself. In a letter to the Gardener's Chronicle of May 12, 1860, he wrote:To me the conception of this law of Nature came intuitively as a self-evident fact, almost without an effort of concentrated thought. Mr. Darwin here seems to have more merit in the discovery than I have had—to me it did not appear a discovery. He seems to have worked it out by inductive reason, slowly and with due caution to have made his way synthetically from fact to fact onwards; while with me it was by a general glance at the scheme of Nature that I estimated this select production of species as an a priori recognisable fact—an axiom, requiring only to be pointed out to be admitted by unprejudiced minds of sufficient grasp.¹²⁵ In the same letter, Matthew maintained that his ideas had not been accepted because the age was not ripe for such ideas.¹²⁶ Nor, he said, was the present age. He considered the inability of most of Darwin's critics to grasp his theory to be incurable. Yet he did not argue that natural selection should be accepted because of the evidence, but rather, that it should be accepted on faith:Belief here requires a certain grasp of mind. No direct proof of phenomena embracing so long a period of time is within the compass of short-lived man. To attempt to satisfy a school of ultra skeptics, who have a wonderfully limited power of perception of means to ends... would be labour in vain.... They could not be brought to conceive the purpose of a handsaw though they saw its action, if the whole individual building it assisted to construct were not presented complete before their eyes... Like a child looking upon the motion of a wheel in an engine they would only perceive and admire... without noticing its agency in... affecting the purposed end.¹²⁷ Here, then, is the final irony. In a passage urging acceptance of Darwin's theory, a theory which was to banish design and purpose from the natural world, we find echoes of Paley and of Providence.Loren Eiseley has lamented the fact that Matthew did not bring his views into the open, because the amount of ground he was able to cover in a few paragraphs suggests that he might have been able to sustain a longer treatise.¹²⁸ Now that the intellectual and historical context of Matthew's ideas are known, this statement is no longer tenable. Matthew was not a scientist, and his books were not written as biological treatises. His discussions of natural selection were not attempts to cover ground in advancing a particular scientific theory, but were simply reflections of his own assumptions about the natural world.Furthermore, despite Matthew's acceptance of evolution and natural selection, his biological thought was basically conservative on points where Darwin's was radical. Where Matthew saw a series of stable worlds interrupted by violent upheavals, Darwin saw a continuous process of change in an ever-fluctuating world. Where Matthew conceived of species in terms of Aristotelian classes and essences, Darwin revolutionized our concept of species by treating them as populations. Where Matthew saw a world of design and beauty functioning according to natural laws laid down by benevolent Providence, Darwin abolished design and Providence from nature and ushered in a world which cycles ever onward according to laws of chance and probability.It is not even particularly useful to point to Matthew as evidence that evolution was in the air prior to 1859.¹²⁹ His ideas did not represent the first wave of a coming revolution, but were the product of his own personal philosophical outlook, as expressed in the context of the biological thought of the 1830's. Matthew is important in the history of ideas, not simply because he accepted the concept of evolution or thought of something resembling natural selection, but because he did so without overthrowing, in his own mind, any of the basic philosophical assumptions which had underlain biological science since Aristotle. In recognizing Matthew's failure to do so, we are in a position to appreciate more fully the significance of the Darwinian Revolution.     

Steroid synthesizing cellular sites in the ovary of the domestic pigeon Columba livia (Gmelin): a histochemical study.

Synopsis The ovary of the domestic pigeon,Columba livia, has been assayed histochemically for the localization of ⁵-3-hydroxysteroid dehydrogenase (⁵-3-HSDH), 17-hydroxysteroid dehydrogenase (17-HSDH), 11-hydroxysteroid dehydrogenase (11-HSDH), glucose-6-phosphate dehydrogenase (G6P-DH) and NADH-diaphorase activities during different periods of the reproductive cycle. ⁵-3-HSDH, 17-HSDH, 11-HSDH, G6P-DH and NADH-diaphorase activity was found in the theca interna of growing, atretic and postovulatory follicles, the granulosa of ovulatory, atretic and postovulatory follicles, and interstitial gland cells during the pre-incubation and the laying periods. During the incubation and squab feeding periods only ⁵-3-HSDH, G6P-DH and NADH-diaphorase activities were observed in the above mentioned cells. The steroidogenic potential of atretic follicles depends upon the type of atresia a follicle undergoes.     

Patterned disjunction in Drosophila melanogaster. I. Assortment of SPA pol /+ and X,Y in the stock N1

N1 (= Nijmegen 1) D. melanogaster heterozygous for sparkling poliert (4) (= pol, here) were backcrossed as single pairs. When were not selected for departure from 1/1, pol/pol ⁺, many exceptional ratios were observed even though the net for all 67 pairs was approximately one-to-one; in the same experiment a net excess of was observed. In a second experiment were selected for departure from 1/1, pol/pol ⁺ratios. The net pol/pol ⁺ratios became significantly different from the 1/1 expected but the sex ratio approached normal. Lineage of the males in the second experiment were recorded and displayed as pedigrees. These together with tabulated data suggest that in some pairs, one of the four categories pol , pol , pol ⁺, pol ⁺ may be significantly greater or less than 1/4 of the total offspring recovered.     

The levels of ζ, γ, and δ chains in patients with Hb H disease

Summary Details are given of a study of blood samples from 24 patients with Hb H disease from different Mediterranean countries and from the Far East. Four different types of -thal-1 (--) were observed, namely-() ( 20.5-kb deletion);--MED-I ( 17.5-kb deletion);--MED-II (>26.5-kb deletion); and--SEA ( 18-kb deletion, in Orientals only). The -thal-2 was mainly of the deletion type (16 with the 3.7-kb deletion; 1 with the 4.2-kb deletion), while 4 of the 7 patients with a nondeletional type had the five-nucleotide deletion at the donor splice site of the first intron of the 2 gene. All patients had a mild-to-moderate hemolytic anemia; no significant differences in hematology were observed between the groups. Hb A₂ was decreased to about one-third of the normal level. The Hb H formation varied considerably and its quantitation was not always satisfactory. Patients with Hb H disease due to any -thal-1 combined with a nondeletional -thal-2 had the highest Hb H levels and a more marked anemia. The chain production was small and absent in patients with the MED-II type of -thal-1 because this deletion included the and genes. The highest chain levels were present in the four patients with the SEA type of -thal-1. The chain production was increased, particularly in patients with a mutation of C T at position-158 to the ^G globin gene. This chain was primarily present as Hb Bart's (or ₄) and only about 15% was recovered as Hb F or ₂₂. The evaluation of the rate of chains produced in these patients was greatly facilitated by data from one patient who had Hb H disease and a heterozygosity for the ^A-⁺. The low levels of Hb A₂ and of Hb F (relative to Hb Bart's) can be explained by a decreased affinity of chains for and chains as compared with chains in conditions of severe chain deficiency.     

Significance of the β-Subunit in the Biogenesis of Na+/K+-ATPase

This review summarizes our experiments on the significance of the -subunit in the functional expression of Na⁺/K⁺-ATPase. The -subunit acts like a receptor for the -subunit in the biogenesis of Na⁺/K⁺-ATPase and facilitates the correct folding of the -subunit in the membrane. The -subunit synthesized in the absence of the -subunit is subjected to rapid degradation in the endoplasmic reticulum. Several assembly sites are assigned in the sequence of the -subunit from the cytoplasmic NH₂-terminal domain to the extracellular COOH-terminus: the NH₂-terminal region of the extracellular domain, the conservative proline in the third disulfide loop, the hydrophobic amino acid residues near the COOH-terminus and the cysteine residues forming the second and the third disulfide bridges. Upon assembly, the -subunit confers a resistance to trypsin on the -subunit. The conformations induced in the -subunit of Na⁺/K⁺-ATPase by Na⁺/K⁺- and H⁺/K⁺-ATPase -subunits are somehow different from each other and are named the NK-type and KH-type, respectively. The extracellular domain of the -subunit is involved in the folding of the -subunit leading to trypsin-resistant conformations. The sequences from Cys150 to the COOH-terminus of the Na⁺/K⁺-ATPase -subunit and from Ile89 to the COOH–terminus of the H⁺/K⁺-ATPase -subunit are necessary to form trypsin-resistant conformations of the NK- and HK-type. respectively. The first disulfide loop of the extracellular domain of the -subunits is critical in the expression of functional Na⁺/K⁺-ATPase.     

Effect of the cationic polypeptide polylysine on neutral amino acid transport in isolated brain microvessels

Summary The functionality of isolated brain microvessels — used as anin vitro model of the blood-brain barrier — can be influenced by interaction with cationic proteins. The various polylysines (M_r ranging from 0.9 to 180 kDa) tested affected the activity of both the Na⁺-dependent (A) and the Na⁺-independent (L) systems for neutral amino acid transport. Exposure to the 180 kDa polylysine caused a conspicuous inhibition of both transport systems, associated to an increased passive permeability. There was a constant, M_r-dependent, inhibition of the the L-system-mediated uptake of hydrophobic neutral amino acids. The activity of the A-system was enhanced, upon exposure to polymers larger than 22 kDa reaching its peak at 68 kDa and and declining at higher M_r values. The effect which was Na⁺-ions dependent and abolished by phloretine, could be essentially ascribed to an increased affinity of the MeAIB for its carrier (K_m value decreasing from 265 to 169µM in presence of 68 kDa polylysine).     

<Emphasis Type="Italic">In vitro</Emphasis> screening of sugarcane to evaluate smut susceptibility

Tissue-cultured plantlets of three sugarcane (Saccharum spp.) cultivars having a known field smut reaction were screened for susceptibility to Ustilago scitaminea H&P Sydow. Plantlets were inoculated with 0.5 l of a suspension of equally mixed quantities of plus and minus mating type sporidia of U. scitaminea at concentrations ranging from 1×10¹ to 1×10⁶ cells. Fungal sori (whips) were produced in cultivar N12 (intermediate) 6weeks following inoculation with 1×10⁵ mixed sporidia and thereafter in cultivar NCo310 (susceptible) but not in cultivar N19 (resistant). Sori bearing teliospores were produced up to 3months following inoculation and incubation at 26°C. No sori were produced at mixed sporidial concentrations lower than 1×10⁵cells. The in vitro soral production in cultivars N19, N12 and NCo310 was 0, 27.5 and 47.5% respectively. Plantlets inoculated with 1×105sporidia of only one mating-type did not produce sori in any of the three cultivars tested. Blind scoring of an unknown sugarcane cultivar by this method corresponded exactly with its field smut rating.