Plasmodium falciparum protein associated with the invasion junction contains a conserved oxidoreductase domain

The merozoite cap protein-1 (MCP-1) of Plasmodium falciparum follows the distribution of the moving Junction during invasion of erythrocytes. We have cloned the gene encoding this protein from a cDNA library using a monoclonal antibody. The protein lacks a signal sequence and has no predicted trans-membrane domains; none of the antisera reacts with the surfaces of intact merozoites, indicating that the cap distribution is submembranous. MCP-1 is divided into three domains. The N-terminal domain includes a 52-amino-acid region that is highly conserved in a large family of bacterial and eukaryotic proteins. Based on the known functions of two proteins of this family and the pattern of amino acid conservation, it is predicted that this domain may possess oxido-reductase activity, since the active cysteine residue of this domain is invariant in all proteins of the family. The other two domains of MCP-1 are not found in any other members of this protein family and may reflect the specific function of MCP-1 in invasion. The middle domain is negatively charged and enriched in glutamate; the C-terminal domain is positively charged and enriched in lysine. By virtue of its positive charge, the C-terminal domain resembles domains in some cytoskeleton-associated proteins and may mediate the interaction of MCP-1 with cytoskeleton in Plasmodium.     

Immobilization of tyrosinase for use in nonaqueous media: Enzyme deactivation phenomena

Summary We have investigated features for minimizing the inactivation of tyrosinase (E.C. 1.14.18.1) that is caused by immobilization on glass beads and Celite^®. The degree of inactivation is dependent on the enzyme loading and the carrier's surface area. Addition of a sacrificial protein during the immobilization procedure offers a protective effect with increased residual activity on the basis of comparable enzyme loading.     

Open-field Tests in Host-specificity Determination of Insects for Biological Control of Weeds

Open-field tests may be used for the host-specificity determination of insects used in the biological control of weeds. Such tests allow insects to exercise free choice of plants without constraints associated with the use of cages. Therefore, this testing method can generate host data on candidate biocontrol agents under more natural conditions than those obtained via cage tests. The literature contains 24 studies of open-field testing, involving 13 target weed species, more than 34 species of insects and one eriophyid mite. Field-test data were used to support the release of 20 of these candidate agents into new countries. Most field tests have been conducted in concert with laboratory host-specificity tests or in response to the results of laboratory tests. This review also provides information on experimental designs, locations, categories of test plants included and the constraints of open-field testing.     

Location of the active site of the bean {alpha}-amylase inhibitor and involvement of a Trp, Arg, Tyr triad

Seeds of the common bean contain three homologous proteins:phytohaemagglutinin E, phytohaemagglutinin L and the lectin-likeprotein     

Inward and outward K+-selective currents in the plasma membrane of protoplasts from maize root cortex and stele

In an attempt to understand the processes mediating ion transport within the root, the patch clamp technique was applied to protoplasts isolated from the cortex and stele of maize roots and their plasma membrane conductances investigated. In the whole-cell configuration, membrane hyperpolarization induced a slowly activating inwardly rectifying conductance in most protoplasts isolated from the root cortex. In contrast, most protoplasts isolated from the stele contained a slowly activating outwardly rectifying conductance upon plasma membrane depolarization. The reversal potential of the inward current indicated that it was primarily due to the movement of K⁺; the outwardly rectifying conductance was comparatively less selective for K⁺. Membrane hyperpolarization beyond a threshold of about ?70 mV induced inward currents. When E_K was set negative of this threshold, inward currents activated negative of E_K and no outward currents were observed positive of E_K. Outward currents in the stelar protoplasts activated at potentials positive of ?85 mV. However, when E_K was set positive of ?85 mV a small inward current was also observed at potentials negative (and slightly positive) of the equilibrium potential for K⁺. Inwardly and outwardly rectifying K⁺ channels were observed in outside-out patches from the plasma membrane of cortical and stelar cells, respectively. Characterization of these channels showed that they were likely to be responsible for the macroscopic ‘whole-cell’ currents. Inward and outward currents were affected differently by various K⁺ channel blockers (TEA⁺, Ba²⁺ and Cs⁺). In addition, Ca²⁺ above 1 mM partially blocked the inward current in a voltage-dependent manner but had little effect on the outward current. It is suggested that the inwardly rectifying conductance identified in protoplasts isolated from the cortex probably represents an important component of the low-affinity K⁺ uptake mechanism (mechanism II) identified in intact roots. The outwardly rectifying conductance identified in protoplasts isolated from the stele could play a role in the release of cations into the xylem vessels for transport to the shoot.     

Genetic regulation of gibberellin deactivation in Pisum

The regulation of gibberellin (GA) deactivation was examined using the sin (slender) mutation in the garden pea (Pisum sativum L.). This mutation blocks the deactivation of GA₂₀, the precursor of the bioactive GA₁. Firstly, crosses were made to combine sin with the GA biosynthesis mutations na, lhⁱ and le-3. The combination sin na produced a novel phenotype, with long (‘slender’) basal internodes and extremely short (‘nana’) upper internodes. In contrast, the double mutant sin lhⁱ was phenotypically dwarf. The mutation sin causes an accumulation of GA₂₀ in maturing seeds, and this was unaffected by na, since the na mutation is not expressed in seeds. In contrast, lhⁱ seeds did not accumulate GA₂₀, since lhⁱ imposes an early block on GA biosynthesis. Secondly, the effects of sin on several steps in GA deactivation were investigated. In maturing seeds, the mutation sin blocks two steps in GA₂₀ metabolism, namely, GA₂₀ to GA₂₉, and GA₂₉ to GA₂₉-catabolite. In the vegetative plant, on the other hand, sin blocked the step GA₂₀ to GA₂₉, but not GA₂₉ to GA₂₉-catabolite; the steps GA₂₀ to GA₈₁ and GA₂₀ to GA₁ were also not impaired in this mutant. It is clear that the effects of sin, like those of na, are strongly organ-specific. The presence of separate enzymes for the steps GA₂₀ to GA₂₉ and GA₂₉ to GA₂₉-catabolite was suggested by the observation that GA₈ inhibited the latter step, but not the former, and by the inability of GA₂₀ and GA₂₉ to inhibit each other's metabolism. It is suggested that the Sin gene may be a regulatory gene controlling the expression of two structural genes involved in GA deactivation.     

Mechanisms of genetic control of immune responses

We examined multiple genetically regulated Immoral and cell-mediated immune (CMI) responses to poly(glu⁶⁰ala³⁰tyr¹⁰) (GAT) using a panel of mouse strains. We show that assignment of responder/nonresponder status depends upon the assay method. In addition, two distinct categories of nonresponder mice were found: (1) those which are unresponsive by all parameters tested (H-2 ^q and H-2 ^s haplotypes) and (2) those which are partially nonresponsive [H-2 ^bm12 mutant strain—a low/nonresponder by splenic plaque-forming cell (PFC) and delayed-type hypersensitivity (DTH) responses, but exhibits B6 parental levels of high GAT-specific T-cell proliferation (Tprlf) and interleukin-2 production]. The distinction between these two nonresponder types was confirmed by complementation tests in which significant GAT-specific PFC and DTH responses were seen in (H-2 ^q × H-2 ^bm12)F₁ hybrids, but not in (H-2 ^q × H-2 ^s )F₁ hybrids. Suppressor T cells (Ts) also play a selective role in nonresponsiveness to GAT. Cyclophosphamide treatment of nonresponders (to eliminate Ts activity) as well as immunization with GAT coupled to the immunogenic carrier MBSA result in the development of GAT-specific humoral, but not CMI responses. Our results indicate that the T cell is the cellular site of Ir gene expression and that Tprlf responses do not correlate with functional helper T-cell activity and suggest distinct, multi-step Th/Ts regulatory pathways in the development of humoral and CMI effector functions.     

Heterokaryon Identification Through Simultaneous Fluorescence of Tetramethylrhodamine Isothiocyanate and Fluorescein Isothiocyanate Labelled Protoplasts

Protoplasts were separately stained with the fluorescent dyes fluorescein iso-thiocyanate (FITC) and tetramethylrhodamine isothiocyanate (TRITC). Following fusion, doubly stained heterokaryons were identified under fluorescence microscopy by using the Zeiss filter set 48 77 05 (excitation filter 450-490 nm, dichroic reflector 510 nm, and barrier filter 520 nm) which allowed simultaneous fluorochrome emissions. Previously, either emisson spectrum, but not both, was possible for any single filter set.     

On the multiplicity of platelet prostaglandin receptors: II. The use of N-0164 for distinguishing the loct of action for PGI2, PGD2, PGE2 and hydantoin analogs

The ω-chain variant analogs of prostacyclin (PGI₂) and PGD₂ in which the n-amyl side-chain has been replaced by a cyclohexyl group have been prepared and their cardiovascular activities have been compared to those of BW-245C(Fig. 1)(1) a potent anti-aggregatory vasodilator bearing a cyclohexyl-terminated side-chain on a hydantoin skeleton. The cyclohexyl group has little effect on PGI₂, but converts PGD₂ to a long lasting hypotensive agent and increases the platelet anti-aggregatory potency of PGD₂ by a factor of 8. The prostaglandin antagonist N-0164 selectively blocks the anti-aggregatory actions of PGD₂, cyclohexyl-PGD₂, and BW-245C; with essentially no effect on PGI₂, cyclohexyl-PGI₂ and PGE₂ at comparably effective doses. The latter observation is contrary to an earlier report by MacIntyre (2,3), but supports the view that the anti-aggregatory effect of high doses of PGE₂ ($\text{EC}{}_{50}\text{=50μ}\text{M}$) is mediated by the PGI₂ receptor (4). The hydantoin acts at the platelet PGD₂ receptor.     

Isolation and amino-terminal sequences of subunits from the photosynthetic reaction center of Rhodopseudomonas capsulata

The amino-terminal sequences have been determined by Edman degradation for the reaction center polypeptides from a carotenoidless mutant of Rhodopseudomonas capsulata. Individual polypeptides were isolated by preparative electrophoresis and electroelution. By comparison with the sequences deduced from the DNA (Youvan, D.C., Alberti, M., Begush, H., Bylina, E.J. and Hearst, J.E. (1984) Proc. Natl. Acad. Sci. USA 81, 189–192) we conclude that the M and L subunits are processed so as to remove the amino-terminal methionine, whereas the H subunit is not processed at the amino-terminus after translation. None of the subunits is synthesized with a significant amino-terminal extension peptide.