Pattern-specific contrast threshold elevation

Visual channels are defined psychophysically; stimuli that interact share information in the same channel, and those that do not interact are processed in different channels. Channels are often investigated by means of adaptation to one stimulus, testing contrast threshold elevation with one (or more) others. Much recent work has tested the tuning of channels for orientation and spatial frequency, using simple line gratings. This study examined the pattern-specificity of such adaptation, testing the hypothesis that the fundamental operators of the Lie Transformation Group Theory of Neuropsychology (LTG/NP) define psychophysical channels. In Experiment I the three basic pattern pairs of LTG/NP were used as adaptation and test stimuli in a conventional contrast threshold-elevation experiment. Threshold elevation was pattern-specific, thus supporting the hypothesis. In subsequent experiments various 'fractured' patterns, and patterns generated by combinations of Lie operators were used both for adaptation and test. The results were mixed; some supported the original hypothesis, but many did not. Relations between local contour orientations in adaptation and test patterns could explain some results, but not all. The hypothesis that adaptation occurs to the oriented spatial-frequency components of the test patterns, on the other hand, gave a good fit to the data. It is concluded that there is pattern-specificity in contrast threshold elevation, but it is a form of specificity that can be explained without recourse to a model of geometrical pattern processing, at least for the simple patterns used here.     

Thin-film antimony-antimony-oxide enzyme electrode for penicillin determination

A potentiometric penicillinase electrode is reported in which the base pH transducer is a thin-film anti-mony-antimony-oxide electrode deposited by vacuum evaporation. Several enzyme immobilization procedures have been examined and a crosslinked protein film found to be the most appropriate to this type of sensor. The use of an adjacent antimony-antimony-oxide track as a pseudoreference electrode was successfully demonstrated. The overall response was shown to be independent of the stirring rate above 100 rpm, but the kinetics of the response were found to depend markedly on the stirring rate. The intrinsic linear response range was 3 x 10(-4)Mto 7 x 10(-3)M penicillin G. Linearizing transforms that extend the useful range were examined.     

Creatine kinase isoenzymes in Torpedo californica: absence of the major brain isoenzyme from nicotinic acetylcholine receptor membranes

Creatine kinase, actin, and nu 1 are three proteins of Mr 43 000 associated with membranes from electric organ highly enriched in nicotinic acetylcholine receptor. High levels of creatine kinase are required to maintain adequate ATP levels, while actin may play a role in maintaining the synaptic cytoskeleton. Previous investigations have prompted the conclusion that postsynaptic specializations at the receptor-enriched membrane domains in electroplax contain the brain form of creatine kinase rather than the form of creatine kinase predominantly found in muscle. We have examined this conclusion by purifying Torpedo brain creatine kinase to virtual homogeneity in order to examine its immunochemical, molecular, and electrophoretic properties. On the basis of immunological cross-reactivity and isozyme analysis, the receptor-associated creatine kinase is identified to be of the muscle type. When the molecular characteristics of Torpedo brain and muscle creatine kinase are compared, the brain enzyme is positioned at a more basic pH during chromatofocusing and on two-dimensional gel electrophoresis (pI = 7.5-7.9). Furthermore, electrophoretic mobilities of the brain and muscle forms of creatine kinase differ in sodium dodecyl sulfate electrophoresis: the brain isozyme of creatine kinase has lower apparent molecular weight (Mr 41 000) when compared with the muscle enzyme (Mr 43 000). On the basis of the results of our current investigations, the hypothesis that the brain isozyme of creatine kinase is a component of the postsynaptic specializations of the Torpedo californica electroplax must be abandoned. Recent sequence data have established close homology between Torpedo and mammalian muscle creatine kinases. On the basis of electrophoretic criteria, our results indicate that a lower degree of homology exists between the brain isozymes.     

pH-dependent processes in proteins

Recent improvements in the understanding of electrostatic interactions in proteins serve as a focus for the general topic of pH-dependent processes in proteins. The general importance of pH-dependent processes is first set out in terms of hydrogen ion equilibria, stability, ligand interactions, assembly, dynamics, and events in related molecular systems. The development of various theoretical treatments includes various formalisms in addition to the solvent interface model developed by Shire et al. as an extension of the Tanford-Kirkwood treatment. A number of detailed applications of the model are presented and future potentialities are sketched.     

Comparison of patterns of hybrid resistance to the BALB/c plasmacytomas LPC-1 and MPC-11

Summary Patterns of genetic control of hybrid resistance to the BALB/c plasmacytoma LPC-1 were studied for comparison with those to MPC-11, a plasmacytoma investigated previously. The overall patterns of hybrid resistance to the two tumors were similar, i.e., hybrids between BALB/c and BALB congenic resistant (CR) strains, A and A CR strains, SJL and DBA/2 were as susceptible to LPC-1 as BALB/c mice themselves, whereas hybrids between BALB/c and AKR, C57BL/Ks, DBA/1, C57BL/6 (B6), C57BL/10 (B10) and B10 CR strains were resistant to LPC-1 as previously shown with MPC-11. Heterozygosity within the H-2 complex alone was insufficient for resistance to either tumor. Among hybrids between BALB/c and the B10 CR strains, however, the presence of certain H-2 haplotypes influenced the degree of resistance seen and this H-2 effect was different for the two tumors. A sex effect on resistance to LPC-1, but not to MPC-11, was seen among F₁ hybrids between BALB/c and DBA/1 although not in any other F₁ hybrids. Among ((B10×BALB/c)F₁×BALB/c) and (BALB/c×(B10×BALB/c)F₁) and ((BALB/c×B10)F₁×BALB/c) and ((BALB/c×B10)F₁×BALB/c) backcross mice, however, significantly more males than females were resistant to LPC-1 and the results of this study are compatible with the idea that in F₁ hybrids between BALB/c and B10, resistance to LPC-1 is controlled by two dominant autosomal genes, one of which is sex-limited and neither of which is linked to H-2. In contrast, hybrid resistance to MPC-11 in this cross is controlled by a single gene. Cross-protection experiments indicated that the two tumors share at least one tumor-associated transplantation antigen.     

Iodoazomycin riboside (1-(5'-iodo-5'-deoxyribofuranosyl)-2-nitroimidazole), a hypoxic cell marker. I. Synthesis and in vitro characterization

Misonidazole (MISO), a selective radiosensitizer of hypoxic cells, forms adducts with cellular biomolecules with rates which are 30-50 X higher under hypoxic as compared to aerobic conditions of incubation. This technique of sensitizer adduct formation was proposed as a possible means of measuring the hypoxic fraction of solid tumors by noninvasive procedures. Iodoazomycin riboside (5'-IAZR) and 5'-[125I]AZR were synthesized and chemically characterized. Measurements of in vitro cytotoxicity and radiosensitizing ability with EMT-6 tumor cells in vitro indicated that 5'-IAZR is approximately 3 X more toxic and effective than is azomycin riboside (AZR) and approximately 10 X more toxic and effective than is MISO. 5'-[125I]AZR was shown to selectively bind to hypoxic EMT-6 cells at rates which were 2.5-3 X faster than those of MISO. The absolute rates of binding of 5'-IAZR to hypoxic cells at concentrations of 10-100 microM are the highest observed in this laboratory for any hypoxic cell radiosensitizer tested to date. These data suggest that 5'-IAZR, when labeled with an appropriate radioisotope (e.g., 131I), might be a useful marker for hypoxic cells in solid tumors amenable to noninvasive detection. Additional studies with animal tumor models appear to be warranted.     

Some Properties of Thiosulfate-Oxidizing Enzyme from Marine Heterotroph 16B

Thiosulfate-oxidizing enzyme has been demonstrated in cell-free extracts of the marine, thiosulfate-oxidizing pseudomonad strain 16B. The enzyme, partially purified by ion-exchange chromatography and calcium phosphate gel treatment, catalyzed the oxidation of thiosulfate to tetrathionate with the concomitant reduction of ferricyanide. Native but not mammalian cytochrome c was also reduced by the enzyme in the presence of thiosulfate. The enzyme was located exclusively in the supernatant of ultracentrifuged cell extracts. The most purified enzyme preparation, like intact cells, exhibited a temperature optimum of 30 to 31°C. However, it exhibited no definite pH optimum. At pH 6.1 to 6.3 and 30°C, the K_m for thiosulfate was 1.57 mM. At lower temperatures, the apparent K_m for thiosulfate increased, but the apparent maximum velocity remained virtually unchanged. Thiosulfate oxidation in intact cells exhibited an increase in the pH optimum at lower temperatures. The thiosulfate-oxidizing enzyme of marine heterotroph 16B is compared with thiosulfate-oxidizing enzymes from other bacteria, and the effect of temperature on the relationship between pH and thiosulfate oxidation is discussed with reference to the natural habitat of the bacterium.     

Effect of mycorrhizal inocula on the growth of Sitka spruce seedlings in different soils

Summary Different mycorrhizal fungi were tested for their effectiveness in promoting growth of Sitka spruce seedlings, in two contrasting soils, in a glasshouse pot experiment. In nursery soil,Laccaria amethystina significantly improved growth of seedlings in comparison toL. laccata. Seedlings inoculated with a forest isolate ofThelephora terrestris were significantly larger than those inoculated with a nursery isolate when grown in forest soil. The effectiveness ofComplexipes moniliformis in forest soil was poor in comparison to other mycorrhizal fungi. Strains aswell as species of mycorrhizal fungi affect seedling growth differently. These effects are further influenced by soil type.