Evolution of catalytic proteins

Summary It is believed that all present-day organisms descended from a common cellular ancestor. Such a cell must have evolved from more primitive and simpler precursors, but neither their organization nor the route such evolution took are accessible to the molecular techniques available today. We propose a mechanism, based on functional properties of enzymes and the kinetics of growth, which allows us to reconstruct the general course of early enzyme evolution. A precursor cell containing very few multifunctional enzymes with low catalytic activities is shown to lead inevitably to descendants with a large number of differentiated monofunctional enzymes with high turnover numbers. Mutation and natural selection for faster growth are shown to be the only conditions necessary for such a change to have occurred.     

Knob heterochromatin homology in maize and its relatives

Summary We have characterised the major DNA sequence component of knob heterochromatin in maize, teosinte andTripsacum. Sequence analysis of this DNA gives strong support to the proposal that maize originated by selection of variants in teosinte. In situ hybridization has confirmed that this repeating DNA sequence, which is the major component of maize knob heterochromatin, is also the major component of knobs in teosinte,Zea diploperennis andTripsacum. In Southern blot hybridizations the repeat has a similar basic organization in all taxa;Tripsacum, however, is differentiated from maize and teosinte by a number of sequence features. Maize and teosinte knob heterochromatin are indistinguishable with regard to the distribution of mutations in the 180-bp repeat and the presence and organization of a 202-bp variant sequence. The knob DNA sequence was not detectable in three species ofCoix, an Old World genus of the Maydeae.Within the repeat unit is a 27-bp region that shows no sequence changes in maize, teosinte orTripsacum. The remainder of the repeat unit has randomly distributed nucleotide changes. The presence of the conserved sequence region suggests that knob DNA may have a functional role in the nucleus.     

Locus determining the human sperm-specific lactate dehydrogenase,LDHC, is syntenic with LDHC

From the data presented in this report, the human LDHC gene locus is assigned to chromosome 11. Three genes determine lactate dehydrogenase (LDH) in man. LDHA and LDHB are expressed in most somatic tissues, while expression of LDHC is confined to the germinal epithelium of the testes. A human LDHC cDNA clone was used as a probe to analyze genomic DNA from rodent/human somatic cell hybrids. The pattern of bands with LDHC hybridization is easily distinguished from the pattern detected by LDHA hybridization, and the LDHC probe is specific for testis mRNA. The structural gene LDHA has been previously assigned to human chromosome 11, while LDHB maps to chromosome 12. Studies of pigeon LDH have shown tight linkage between LDHB and LDHC leading to the expectation that these genes would be syntenic in man. However, the data presented in this paper show conclusively that LDHC is syntenic with LDHA on human chromosome 11. The terminology for LDH genes LDHA, LDHB, and LDHC is equivalent to Ldhl, Ldh2, and Ldh3, respectively.     

Relationship between chloroplast structure and O2 evolution rate of leaf discs in plants from different biotopes in South Finland

Abstract The chloroplast ultrastructure, especially the thylakoid organization, the polypeptide composition of the thylakoid membranes and photosynthetic O₂ evolution rate, chlorophyll (Chl) content and Chi a/b ratio were studied in leaves of nine plants growing in contrasting biotopes in the wild in South Finland. All the measurements were made at the beginning of the period of main growth on leaves approaching full expansion, when the CO₂-saturated O₂ evolution rate (measured at 20°C and 1500 μmol photons m^?2s^?1) was at a maximum, ranging from 19.2 to 6.9 μmol O₂ cm^?2 h^?1. Among the species, the Chi a/b ratio varied between 3.75 and 2.71. In the mesophyll chloroplasts, the ratio of the total length of appressed to non-appressed thylakoid membranes varied between 1.07 and 1.79, the number of partitions per granum varied between 2.8 and 12.0 and the grana area between 21 and 42% of the chloroplast area. There was a significant relationship between the rate of O₂ evolution of the leaf discs and the thylakoid organization in the mesophyll chloroplasts. The higher the O₂ evolution rate, the lower was the ratio of the total length of appressed to non-appressed thylakoid membranes and also the lower the grana area. Although the relationship of the photosynthetic rate with the Chi content and the Chi a/b ratio of the leaves was not as clear, a significant negative correlation existed between the Chi a/b ratio and the ratio of appressed to non-appressed thylakoid membranes, indicating lateral heterogeneity in the distribution of different Chl- protein complexes.     

Manganese-histidine cluster as the functional center of the water oxidation complex in photosynthesis

The recent model of Kambara and Govindjee for water oxidation [Kambara T. and Govindjee (1985) Proc. Natl. Acad. Sci. U.S.A., 82:6119–6123] has been extended in this paper by examining all the data in order to identify the most likely candidate for the redox-active ligand (RAL), suggested to operate between the water oxidizing complex (WOC) and Z, the electron donor to the reaction center P680. We have concluded that a very suitable candidate for RAL is the imidazole moiety of a histidine residue. The electrochemical data available on imidazole derivatives play heavily in this identification of RAL. Thus, we suggest that histidine might play the role of an electron mediator between the WOC and Z. A model of S-states in terms of their plausible chemical identity is presented here.Abbreviations J electronic spin of ion - P680 reaction center chlorophyll - RAL Redox active ligand - S_n state of the oxygen-evolving system - WOC water oxidation complex - Z electron donor to P680 Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement     

Entropy in evolution

Daniel R. Brooks and E. O. Wiley have proposed a theory of evolution in which fitness is merely a rate determining factor. Evolution is driven by non-equilibrium processes which increase the entropy and information content of species together. Evolution can occur without environmental selection, since increased complexity and organization result from the likely capture at the species level of random variations produced at the chemical level. Speciation can occur as the result of variation within the species which decreases the probability of sharing genetic information. Critics of the Brooks-Wiley theory argue that they have abused terminology from information theory and t thermodynamics. In this paper I review the essentials of the theory, and give an account of hierarchical physical information systems within which the theory can be interpreted. I then show how the major conceptual objections can be answered.     

Reproductive structures and phylogenetic significance of extant primitive Angiosperms

A brief survey is presented on fossil reproductive structures of early Angiosperms from the Lower and mid-Cretaceous and at the same time on the reproductive structures of those extant Angiosperms which resemble most closely these fossils and which seem to be especially primitive also on other grounds: a first group (Degeneriaceae, Himantandraceae, Eupomatiaceae, Austrobaileyaceae) possessing relatively complicated and conspicuous flowers with elaborated inner staminodes, a second group (Chloranthaceae, Trimeniaceae, Amborellaceae) possessing small and relatively simple, inconspicuous flowers with peculiar features in the carpels, and a third group (Winteraceae) possessing flowers with unusual variability in organ number and size. The three groups exhibit a certain diversity in pollination biology, although cantharophily seems to prevail, however different the cantharophily character syndromes may be between the groups. In the extant primitiveMagnoliidae variability occurs on other morphological levels than in the higher advanced Angiosperms. This has to be taken into consideration in evaluations of the systematic relationships of the various groups of theMagnoliidae. Presumably often their relationships are closer than it may appear at first sight. This is also true for the three groups here discussed.     

The daily timing of lamprey attacks

Synopsis Laboratory and field data suggest that several species of parasitic lampreys forage primarily at night, but data forPetromyzon marinus are equivocal. Nocturnal foraging may minimize predation risk. This may be particularly important to those species of lampreys that inhabit shallow streams. Nocturnal foraging also may enhance foraging efficiency if potential hosts at night are quiescent and more easily approached. Future experiments should be designed to avoid several potential sources of bias.     

Karyotype and C-banding inTrigonella sectionFoenumgraecum (Fabaceae)

The six species of the sectionFoenum-graecum ofTrigonella have the same chromosome number, 2n = 16.T. gladiata andT. cariensis have fairly symmetrical karyotypes, while those ofT. foenum-graecum, T. berythea, T. macrorrhyncha andT. cassia are asymmetrical. C-bands are present in all six species but the number of bands and their positive vary considerably among the species. The karyotype evidence suggests that none of the available species of theFoenum-graecum section can be considered as the wild progenitor of fenugreek.     

Effects of physical and chemical treatments on chloroplast manganese. NMR and ESR studies

Measurements were made of the water proton relaxation rate (T^?1₂ = R₂), electron spin resonance (ESR) six-line signal of ‘free’ Mn²⁺, and O₂-evolution activity in thylakoid membranes from pea leaves. The main results are: (1) Aging of thylakoids at 35°C causes a parallel decrease in O₂-evolution activity, in R₂ and in the content of bound Mn, suggesting that R₂ may be related to the loosely bound Mn involved in O₂ evolution. (2) Treatment of thylakoids with tetraphenylboron (TPB) at [TPB] > 2 mM produces a 2-fold increase in R₂, without release of Mn²⁺. The titration curve exhibits three sharp end points. The first end point occurs at a $\text{[}\text{TPB}\text{]}\text{[}\text{chlorophyll}\text{]}$ of 1.25, at which the O₂ evolution is completely inhibited. (3) Treatment of thylakoids with NH₂OH also increases R₂ by nearly 2-fold, either by the reduction of the higher oxidation states of Mn to Mn²⁺ and / or by exposing the Mn to solvent protons. Also, progressive release of bound Mn occurs at [NH₂OH] ≥ 1 mM as shown by an increase increase in the Mn²⁺ ESR signal and a decrease in R₂. (4) Addition of H₂O₂ (0.1–1.0%) to thylakoids causes an enhancement of R₂ similar to that by NH₂OH, but without the release of Mn²⁺. (5) Heat treatment of thylakoids at 40–50°C releases Mn²⁺ and increases R₂. Conversely, pH values of 7 to 4 release Mn²⁺ without changing R₂ while pH values of 7–9 increase R₂ without releasing Mn²⁺. Thus, both high and low pH values as well as the heat treatment cause structural changes enhancing the relaxivity of the bound Mn or of other paramagnetic species.