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.     

Effect of alkyl side chain variation on the electron-transfer activity of ubiquinone derivatives

The effect of the alkyl side chain of the ubiquinone molecule on the electron-transfer activity of ubiquinone in mitochondrial succinate-cytochrome c reductase is studied by using synthetic ubiquinone derivatives that possess the basic ubiquinone structure of 2,3-dimethoxy-5-methyl-1,4-benzoquinone with different alkyl side chains at the 6-position. The alkyl side chains vary in chain length, degree of saturation, and location of double bonds. When a ubiquinone derivative is used as an electron acceptor for succinate-ubiquinone reductase, an alkyl side chain of six carbons is needed to obtain the maximum activity. However, when it serves as an electron donor for ubiquinol-cytochrome c reductase or as a mediator in succinate-cytochrome c reductase, an alkyl side chain of 10 carbons gives maximal efficiency. Introduction of one or two isolated double bonds into the alkyl side chain of the ubiquinone molecule has little effect on electron-transfer activity. However, a conjugated double bond system in the alkyl side chain drastically reduces electron-transfer efficiency. The effect of the conjugated double bond system on the electron-transferring efficiency of ubiquinone depends on its location in the alkyl side chain. When location is far from the benzoquinone ring, the effect is minimal. These observations together with the results obtained from photoaffinity-labeling studies lead us to conclude that flexibility in the portion of the alkyl side chain immediately adjacent to the benzoquinone ring is required for the electron-transfer activity of ubiquinone.     

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.     

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     

Inhibitton of prolactin release by stimulation of presynaptic serotonin autoreceptors

The effects of 5-methoxy-N, N-dimethyltryptamine (5-MeODMT), a serotonin agonist with a preferential action on presynaptic autoreceptors, on prolactin release in male rats was determined. Basal serum prolactin levels were not altered after administration of 1.0, 2.0, 5.0, 10.0 or 20.0 mg/kg of 5-MeODMT.Pretreatment with 5-MeODMT reduced prolactin release by agents that depend on serotonergic neurotransmission for part of their prolactin release stimulation. Prolactin release in response to L-5-hydroxytryptophan (5-HTP) or morphine was significantly reduced by pretreatment of the rats with 5-MeODMT.The results of this experiment indicate that 5-MeODMT act as a presynaptic serotonin autoreceptor stimulant and not as a postsynaptic serotonin agonist on the neuronal systems that control prolactin release.