The absolute efficiency of perceptual decisions

Our perceptions of the world around us are stable and reliable. Is this because the mechanisms that yield them are crude and insensitive and thus immune to false responses? Or is it because a statistical censor that blocks unreliable messages intervenes between the signals from our sense organs and our knowledge of them? This question can be answered by measuring the efficiency with which statistical information is utilized in perception. It is shown that mirror symmetry can be detected in displays of otherwise random dots with an efficiency of up to 50%; thus the statistical mechanisms are not crude and insensitive, and this aspect of sensory physiology and psychology may deserve more attention.     

Direct observation of the enzyme-intermediate complex of 5-enolpyruvylshikimate-3-phosphate synthase by 13C NMR spectroscopy

The interaction of 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, 4,5-dideoxyshikimate 3-phosphate (ddS3P), and [2-13C]-and [3-13C]phosphoenolpyruvate (PEP) has been examined by 13C NMR spectroscopy. Although no resonances due to a dead-end intermediate complex could be detected, an enzyme active site specific formation of pyruvate was observed. The interaction of EPSP synthase with shikimate 3-phosphate (S3P) and [2-13C]- or [3-13C]PEP has been examined by 13C NMR spectroscopy. With [2-13C]PEP, in addition to the resonances due to [2-13C]PEP and [8-13C]EPSP, new resonances appeared at 164.8, 110.9, and 107.2 ppm. The resonance at 164.8 ppm has been assigned to enzyme-bound EPSP. The resonance at 110.9 ppm has been assigned to C-8 of an enzyme-free tetrahedral intermediate of the sort originally proposed by Levin and Sprinson [Levin, J. G., & Sprinson, D. B. (1964) J. Biol. Chem. 239, 1142-1150] and recently independently observed by Anderson et al. [Anderson, K. S., Sikorski, J. A., Benesi, A. J., & Johnson, K. A. (1988) J. Am. Chem. Soc. 110, 6577-6579]. The resonance at 107.2 ppm has been assigned to an enzyme-bound intermediate whose structure is closely related to that of the tetrahedral intermediate. With [3-13C]PEP, new resonances appeared at 88.9, 26.2, 25.5, and 24.5 ppm. The resonance at 88.9 ppm has been assigned to enzyme-bound EPSP. The resonance at 26.2 ppm, which was found to correlate with 1.48 ppm by isotope-edited multiple quantum coherence 1H NMR spectroscopy, has been assigned to the methyl group 4-hydroxy-4-methylketoglutarate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification of proteins from polyacrylamide gels, free of detergent or dye

A two step procedure recovers proteins from sodium dodecyl sulfate polyacrylamide gels. The proteins are eluted by electrophoretic dialysis. The eluent is then passed through an Amberlite CG-400 anion-exchange resin. The recovery of protein is nearly total. The recovered proteins have no detectable sodium dodecyl sulfate contamination. With gels that have been stained with Coomassie Brilliant Blue R, the procedure recovers the proteins free of the dye. We have used this procedure successfully during the purification of epidermal glycoproteins.     

REPRODUCTIVE MATURITY AND SEASONALITY OF MALE SPOTTED DOLPHINS, STENELLA ATTENUATA, IN THE EASTERN TROPICAL PACIFIC

We estimated age at attainment of sexual maturity and examined reproductive seasonality for male spotted dolphins, Stenella attenuata , from the eastern tropical Pacific Ocean. Maturity was determined by histological examination of testes. Average age at sexual maturation was 14.7 yr (the mean of two readers' age estimates). Testis and epididymis weight and seminiferous tubule diameters were reliable indicators of maturity, whereas age, length and color phase were less reliable. Seasonality was determined by changes in testis and epididymis weight, relative quantity of spermatids and spermatozoa, and lumen diameter, as well as an index of testis development (weight of the right testis and epididymis divided by length of the right testis). Testis and epididymis weights and index values peaked in July and August, midway between two predicted mating seasons for the northern offshore stock, but spermatozoa levels were elevated during the predicted breeding seasons.     

Heat stability and pH activity data of alpha-L-fucosidase in human serum vary with enzyme concentration

alpha-L-Fucosidase from serum of humans with either high or low enzyme activity was separately purified. the enzyme from either source had virtually the same heat stability and pH activity profile. It has been widely reported that alpha-L-fucosidase in crude sera from individuals with high and low enzyme activity differed with respect to heat stability and activity at pH 4 relative to activity at pH 5, the pH optimum of the enzyme. We investigated this discrepancy and found that both the heat stability and relative activity at pH 4 of alpha-L-fucosidase from sera with either high or low enzyme activity was dependent upon enzyme concentration. With decreasing enzyme concentration, the enzyme was more heat labile and had less relative activity at pH 4. Consequently, if the data obtained using high and low enzyme activity sera are compared on the basis of equivalent amounts of serum instead of equivalent amounts of enzyme activity, differences between the enzyme from high and low activity serum would be erroneously inferred. Apparently, this is what other investigators have done. Moreover, we found that alpha-L-fucosidase can exist in heat-stable or labile species with sedimentation coefficients of 9.8 S and 4.8 S, respectively. The interconversion and relative proportion of these species is dependent upon enzyme concentration and pH.     

Isolation of cDNA clones for basal lamina components: type IV procollagen

We have isolated cDNA clones for mouse type IV procollagen from a library constructed from total poly A+RNA of 13.5 day mouse embryo parietal endoderm (PE) cells. In Northern analysis these clones hybridise to a 6.8 kb RNA which is abundant in embryonic PE cells and in differentiated F9 teratocarcinoma cells. Hybrid selection and in vitro translation of the cDNA specific mRNA produced a single polypeptide of Mr = 165 000. This polypeptide was specifically immunoprecipitated with mouse type IV procollagen antisera and comigrated on SDS-gel electrophoresis with one of the two in vitro synthesised chains of type IV procollagen. Undifferentiated F9 teratocarcinoma cells can be induced by retinoic acid and dibutyryl cAMP to differentiate in vitro into endoderm-like cells which resemble mouse PE cells in synthesising large amounts of basement membrane proteins, including type IV procollagen. Here we show, using one of the cDNA clones as a probe for type IV procollagen, that an increase in cellular concentration of type IV procollagen mRNA occurs within 24 to 48 hours of induction, reaching a constant high level by 72 hours.