The conversion of tubulin carboxyl groups to amides has a stabilizing effect on microtubules.

In a recent study, we demonstrated that the conversion of carboxyl residues in the C-termini of tubulin to neutral amides with glycine ethyl ester enhanced the ability of the protein to assemble into microtubules and decreased its interaction with microtubule-associated proteins (MAPs). In this work, we investigated the effects of carboxyl modification on the dynamic behavior of microtubules at polymer mass steady state. After steady state, microtubules assembled from unmodified tubulin were sheared, and the mean polymer lengths decreased to 5 microns and then increased to 29 microns within 130 min. In contrast, lengths of sheared microtubules polymerized from tubulin containing 23 modified carboxyl groups increased by only 2-fold. Stabilization of polymer lengths was also observed directly by video-enhanced light microscopy of microtubules grown off of axonemes. Rapid shortening was seen in microtubules composed of unmodified but not modified tubulin. Further evidence for the less dynamic behavior of microtubules as a result of carboxyl modification was obtained from kinetic studies of the elongation phase during assembly which showed a 3-fold lower off-rate constant, k-, for modified microtubules. Another effect of the modification was a 12-fold reduction in the steady-state rate constant for GTP hydrolysis (165 s-1 for unmodified and 14 s-1 for modified). These results suggest that reduction of the negative charges in the C-termini by modification of the acidic residues stabilizes microtubules against depolymerization. MAPs may stabilize microtubules in an analogous manner.     

In vivo EMG biofeedback in violin and viola pedagogy

In vivo EMG biofeedback was found to be an effective pedagogical tool for removing unwanted left-hand tension in nine violin and viola players. Improvement occurred rapidly and persisted throughout a 5-month follow-up period. Further studies will be necessary to assess the effect of biofeedback independent of placebo effects. The brevity of the method and the magnitude of improvement warrant further investigation.     

Unlikelihood that minimal phylogenies for a realistic biological study can be constructed in reasonable computational time

The problem of determining a phylogeny of maximum parsimony from a given set of protein sequences is defined. It is shown that this problem is what is called, in computer science, NP-complete. The implication of this result is that it is equivalent in difficulty to a host of other problems in combinatorial optimization which are notorious for their intractability. This implies that it is more fruitful to attempt to develop heuristic techniques (which do not guarantee maximum parsimony but which do run in reasonable computer time) than to try to develop exact algorithms for phylogeny construction     

Hyperoxia causes increased albumin permeability of cultured endothelial monolayers

The effect of phasic eye movement activity on ventilation during rapid-eye-movement (REM) sleep was studied in seven healthy young adults by use of the respiratory inductive plethysmograph. Mean ventilation (VE) and ventilatory components during REM sleep were not significantly different from that seen in either stages 1-2 or 3-4 sleep. The percent of rib cage contribution to ventilation in REM sleep, 29.3 +/- 5.1%, was reduced compared with 54.4 +/- 5.8% in stage 1-2 and 52.2 +/- 4.3% in stage 3-4 sleep (P less than 0.005). When one separated breaths by the degree of associated phasic eye movement activity, it became apparent that breathing during REM sleep is very heterogeneous. Increasing eye movement activity was associated with inhibition of ventilation with a reduction in VE from 5.1 +/- 0.3 to 3.8 +/- 0.3 l/min. Tidal volume and frequency both fell, whereas inspiratory duration was unchanged. Compartmental ventilation was also affected, with the fall in the rib cage contribution from 37.8 +/- 6.4 to 15.3 +/- 5.6%. Chest wall and abdominal movement became more asynchronous as phasic-eye-movement activity increased and frank paradoxical breathing was seen.     

S-oxalylglutathione is a substrate for gamma-glutamyltransferase (GGT). Implications for the role of GGT in cell proliferation

With glycylglycine or water as acceptor, bovine kidney gamma-glutamyltransferase catalyzes reactions of the known mammalian metabolite, S-oxalylglutathione, at rates comparable to those of L-gamma-glutamyl-p-nitroanilide, a known good substrate. N-Oxalyl-cysteinylglycine is the eventual product of the former reaction. Since oxalyl thiolesters are implicated as important cell proliferation inhibitors, it is proposed that this reaction plays a major role in controlling cell proliferation.     

Electron paramagnetic resonance saturation studies of P-700+ reaction center chlorophyll in plant photosynthesis

Electron paramagnetic resonance (EPR) power saturation and saturation recovery methods have been used to determine the spin lattice, T1, and spin-spin, T2, relaxation times of P-700+ reaction-center chlorophyll in Photosystem I of plant chloroplasts for 10 K less than or equal to T less than or equal to 100 K. T1 was 200 mus at 100 K and increased to 900 mus at 10 K. T2 was 40 ns at 40 K and increased to 100 ns at 10 K. T1 for 40 K less than or equal to T less than or equal to 100 K is inversely proportional to temperature, which is evidence of a direct-lattice relaxation process. At T = 20 K, T1 deviates from the 1/T dependence, indicating a cross relaxation process with an unidentified paramagnetic species. The individual effects of ascorbate and ferricyanide on T1 of P-700+ were examined: T1 of P-700+ was not affected by adding 10 mM ascorbate to digitonin-treated chloroplast fragments (D144 fragments). The P-700+ relaxation time in broken chloroplasts treated with 10 mM ferricyanide was 4-times shorter than in the untreated control at 40 K. Ferricyanide appears to be relaxing the P-700+ indirectly to the lattice by a cross-relaxation process. The possibility of dipolar-spin broadening of P-700+ due to either the iron sulfur center A or plastocyanin was examined by determining the spin-packet linewidth for P-700+ when center A and plastocyanin were in either the reduced or oxidized states. Neither reduced center A nor oxidized plastocyanin was capable of broadening the spin-packet linewidth of P-700+ signal. The absence of dipolar broadening indicates that both center A and plastocyanin are located at a distance at least 3.0 nm from the P-700+ reaction center chlorophyll. This evidence supports previous hypotheses that the electron donor and acceptor to P-700 are situated on opposite sides of the chloroplast membrane. It is also shown that the ratio of photo-oxidized P-700 to photoreduced centers A and B at low temperature is 2 : 1 if P-700 is monitored at a nonsaturating microwave power.     

Absorption of light in photoreceptors: Effect of waveguiding property

The effect of waveguiding property (i.e., the intensity distribution) of the photoreceptor on the number of photons absorbed in a photoreceptor has been studied. It has been found that the effect is significant only for large values of the exposure and the maximum effect is less than 11% in the case of human rod photoreceptor. In the analysis, the funnelling effect, which follows from the coupling between the interior and exterior fields, has not been considered.Work partially supported by the Department of Science and Technology (India)B. D. Gupta is associated with the School of Bioscience Studies     

A numerical taxonomic study of Actinobacillus, Pasteurella and Yersinia

A numerical taxonomic study of strains of Actinobacillus, Pasteurella and Yersinia, with some allied bacteria, showed 23 reasonably distinct groups. These fell into three major areas. Area A contained species of Actinobacillus and Pasteurella: A. suis, A. equuli, A. lignieresii, P. haemolytica biovar A, P. haemolytica biovar T, P. multocida, A. actinomycetemcomitans, 'P. bettii', 'A. seminis', P. ureae and P. aerogenes. Also included in A was a composite group of Pasteurella pneumotropica and P. gallinarum, together with unnamed groups referred to as 'BLG', 'Mair', 'Ross' and 'aer-2'. Area B contained species of Yersinia: Y. enterocolitica, Y. pseudotuberculosis, Y. pestis and a group 'ent-b' similar to Y. enterocolitica. Area C contained non-fermenting strains: Y. philomiragia, Moraxella anatipestifer and a miscellaneous group 'past-b'. There were also a small number of unnamed single strains.