Photosynthetic characteristics of Amaranthus tricolor,a C4 tropical leafy vegetable

The gas exchange characteristics are reported for Amaranthus tricolor, a C₄ vegetable amaranth of southeastern Asia. Maximum photosynthetic capacity was 48.3±1.0μmol CO₂ m^?2s^?1 and the temperature optimum was 35°C. The calculated intercellular CO₂ concentration at this leaf temperature and an incident photon flux (400–700 mm) of 2 mmol m^?2s^?1 averaged 208±14 μl l^?1, abnormally high for a C₄ species. The photosynthetic rate, intercellular CO₂ concentration, and leaf conductance all decreased with an increase in water vapor pressure deficit. However, the decrease in leaf conductance which resulted in a decrease in intercellular CO₂ concentration accounted for only one fourth of the observed decrease in photosynthetic rate as water vapor pressure deficit was increased. Subsequent measurements indicated that the depence of net photosynthesis on intercellular CO₂ concetration changed with water vapor pressure deficit.     

Translation of poly(U) on ribosomes from Streptomyces aureofaciens

Slowly cooled cells of Streptomyces aureofaciens contained mainly tight-couple ribosomes. Maximum rate of polyphenylalanine synthesis on ribosomes of S. aureofaciens was observed at 40°C, while cultures grew optimally at 28°C. Ribosomes of S. aureofaciens differed from those of E. coli in the amount of poly(U) required for maximum synthetic activity. The polyphenylalanine-synthesizing activity of E. coli ribosomes was about 3-times higher than that of S. aureofaciens ribosomes. The addition of protein S1 of E. coli or the homologous protein from S. aureofaciens had no stimulatory effect on the translation of poly(U). In order to localize alteration(s) of S. aureofaciens ribosomes in the elongation step of polypeptide synthesis we developed an in vitro system derived from purified elongation factors and ribosomal subunits. The enzymatic binding of Phe-tRNA to ribosomes of S. aureofaciens was significantly lower than the binding to ribosomes of E. coli. This alteration was mainly connected with the function of S. aureofaciens 50 S subunits. These subunits were not deficient in their ability to associate with 30 S subunits or with protein SL5 which is homologous to L7/L12 of E. coli.     

A Hungarian twin study on hand clasping, arm folding and tongue curling

A twin study was performed in adult Hungarian monozygotic and dizygotic pairs for hand clasping, arm folding and tongue curling. Genetic background of these traits could not be confirmed, although there appears to be a positive correlation between hand clasping type and handedness.     

Tonic and phasic modifications of viscerosensory evoked potentials during sleep in cats

Modification of the viscerosensory evoked potentials (EPs) were studied during the sleep-wakefulness cycle of the rat. Electrical stimuli of various intensity were delivered either to the mucosal surface of a fistula of the small intestine or to the left splanchnic nerve during wakefulness (W), drowsiness (D), slow-wave-sleep (SWS), and paradoxical sleep (PS). The average EPs were recorded from the somatosensory (SI and SII) and associative (AS) areas of the cortex, the ventrobasal complex of the thalamus (VPL), the posterior hypothalamus (HPT) and the dorsal hippocampus (HPC). The amplitude of each component of the EPs in all explored structures were the largest in SWS and the smallest in W. A phasic increase in amplitude was observed in the EPs recorded immediately before the appearance of the spindles of SWS and during the REM episodes of PS. The peak latencies of the late components were the longest in SWS. These changes of the amplitudes and latencies were greater in the responses to weak stimulation than in EPs to strong ones. The possible synaptic events of the sleep-dependent control of viscerosensory activity are discussed.     

Maternal smoking and trisomy among spontaneously aborted conceptions

In a study of spontaneous abortions, we found an apparently robust association of trisomy with smoking that varies with maternal age. Among women under age 30, smoking either before or at the time of conception is less common in women aborting trisomic conceptions than in controls delivering at 28 weeks or later. Among older women, smoking is more common in women aborting trisomic conceptions than in controls. Our results point to an effect of smoking on the frequency of trisomic abortions that varies with age, and they suggest that the causes of recognized trisomic abortions differ in younger and older women.     

Transition-state stabilization at the oxyanion binding sites of serine and thiol proteinases: hydrolyses of thiono and oxygen esters

X-ray diffraction studies suggested that the tetrahedral intermediate formed during the catalysis by serine and thiol proteinases can be stabilized by hydrogen bonds from the protein to the oxyanion of the intermediate [cf. Kraut, J. (1977) Annu. Rev. Biochem. 46, 331-358; Drenth, J., Kalk, K.H., & Swen, H.M. (1976) Biochemistry 15, 3731-3738]. To obtain evidence in favor or against this hypothesis, we synthesized thiono substrates (the derivatives of N-benzoyl-glycine methyl ester and N-acetylphenylalanine ethyl ester) containing a sulfur in place of the carbonyl oxygen atom of the scissile ester bond. We anticipated that this relatively subtle structural change specifically directed to the oxyanion binding site should produce serious catalytic consequences owing to the different properties of oxygen and sulfur if transition-state stabilization in the oxyanion hole is indeed important. In fact, while in alkaline hydrolysis the chemical reactivities of oxygen esters and corresponding thiono esters proved to be similar, neither chymotrypsin nor subtilisin hydrolyzed the thiono esters at a measurable rate. This result substantiates the crucial role of the oxyanion binding site in serine proteinase catalysis. On the basis of the similar values of the binding constants found for oxygen esters and their thiono counterparts, it can be concluded that the substitution of sulfur for oxygen significantly influences transition state stabilization but not substrate binding. The thiol proteinases papain and chymopapain react with the oxygen and thiono esters of N-benzoylglycine at similar rates. Apparently, in these reactions the above stabilizing mechanism is absent or not important, which is a major mechanistic difference between the catalyses by serine and thiol proteinases.     

Mechanism of action of phorbol myristate acetate on human natural killer cell activity

We have investigated the kinetics of inhibition and regeneration of human natural killer (NK) cell-mediated lysis of K562, a human erythroleukemia cell line, by the potent tumor-promoting agent phorbol-12-myristate-13-acetate (PMA). It is shown that PMA inhibits NK cell-mediated cytotoxicity (CMC) in a dose-dependent manner whether the compound is present throughout the 4-hr cytotoxic assay or the effector cells (EC) are pretreated with PMA. Pretreatment of the target cells (TC) with PMA produced a different profile of NK activity suggesting that PMA inhibition of NK-CMC is primarily due to the inactivation of EC. PMA-induced inhibition of NK-CMC does not affect TC binding and is not circumvented by compounds that enhance intracellular levels of cyclic guanosine monophosphate (cGMP) or calcium. Furthermore, and contrary to a recent report, PMA-induced inhibition of NK-CMC is independent of monocytes. Finally, kinetic studies revealed that PMA-induced inhibition of NK-CMC occurs rapidly and is fully reversible provided that “regenerated EC” are thoroughly washed, prior to the cytotoxic assay, to rid the cell suspension of residual PMA. The potential implications of these results to the currently accepted theory of TC destruction by NK cells, the stimulus-secretion model, are discussed.     

Some properties of cardiac troponin T structure.

Troponin T is eluted in multiple peaks when the whole bovine cardiac troponin complex is subjected to DEAE-cellulose chromatography in the presence of 8 M-urea. The heterogeneity observed is due to the presence of two forms of troponin T, differing in their Mr values, amino acid content, degree of phosphorylation and aggregation. Cardiac troponin T contains up to 0.8 mol of phosphate/mol of protein. Rabbit skeletal-muscle troponin T kinase phosphorylates the single site located in the N-terminal pentapeptide of cardiac troponin T. The composition of this peptide, (Ser,Asx,Glx,Glx)Val, is similar to that of skeletal-muscle troponin T. The single thiol group of cardiac troponin T is located some 50-70 residues from the N-terminus. The C-terminal sequence of cardiac troponin T is Trp-Lys, i.e. as is the case of skeletal-muscle troponin T.