Hydroxyproline-Rich Protein Material in Wood and Lignin of Fagus sylvatica

The nitrogen content, distribution, and amino acid composition of protein material were determined in wood and lignin of Fagus sylvatica. The data indicated that the nitrogen originated from hydroxyproline-rich cell wall glycoprotein, about half of which may be bound to the lignin polymer. The implications for lignocellulose biodegradation are discussed.     

pH titration studies of 13C reductively methylated N-terminal serine of glycophorin AM

The ¹³C resonances of N^α,N-[¹³C]dimethylserine of partially ¹³C reductively methylated glycophorin A^M were monitored as a function of pH at 45°C. For comparison, limited data are also presented for the pH dependence of the ¹³C resonances of N^α,N- [¹³C]dimethylserine of fully ¹³C reductively methylated deglycosylated glycophorin A^M. The ‘major’ component of N^α,N- [¹³C]dimethylserine of glycophorin A^M did not titrate, whereas the ‘minor’ component titrated with a pK_a of 7.80 (Hill coefficient of 0.95). Similar results are also indicated for the N^α,N- [¹³C]dimethylserine resonances of ¹³C reductively methylated deglycosylated glycophorin A^M.     

Voltage gating in VDAC is markedly inhibited by micromolar quantities of aluminum

Summary The mitochondrial outer membrane contains voltagegated channels called VDAC that are responsible for the flux of metabolic substrates and metal ions across this membrane. The addition of micromolar quantities of aluminum chloride to phospholipid membranes containing VDAC channels greatly inhibits the voltage dependence of the channels' permeability. The channels remain in their high conducting (open) state even at high membrane potentials. An analysis of the change in the voltage-dependence parameters revealed that the steepness of the voltage dependence decreased while the voltage needed to close half the channels increased. The energy difference between the open and closed states in the absence of an applied potential did not change. Therefore, the results are consistent with aluminum neutralizing the voltage sensor of the channel. pH shift experiments showed that positively charged aluminum species in solution were not involved. The active form was identified as being either (or both) the aluminum hydroxide or the tetrahydroxoaluminate form. Both of these could reasonably be expected to neutralize a positively charged voltage sensor. Aluminum had no detectable effect of either single-channel conductance or selectivity, indicating that the sensor is probably not located in the channel proper and is distinct from the selectivity filter.     

31P nuclear magnetic resonance study of enzymatically phosphorylated glycophorin A

Glycophorin A was phosphorylated using protein kinases and the new protein was investigated using³¹P NMR spectroscopy. Most of these ～30 moles of phosphate were found to be attached to Ser and Thr. Some of these phosphate residues appear to be affected by the carbohydrate residues present. The phosphorylated protein appears to be in a severe state of aggregation, with the degree of aggregationpH-dependent.     

A rhelogical separator for very large DNA molecules.

We present a rheological separation method for DNA molecules in which their deformability is used to advantage. This is the "radial migration method"; here we present experimental verification of the principle, theory having been reported elsewhere. The main conclusions are: (1) the theory is reasonably good; (2) radial migration is highly sensitive to the molecular weight, as predicted, and (3) intact T2 DNA (1.25 X 108 daltons) can be made to migrate about three centimeters in less than three hours.     

Predicting the structures of 18 peptides using Geocore

We describe an extensive test of Geocore, an ab initio peptide folding algorithm. We studied 18 short molecules for which there are structures in the Protein Data Bank; chains are up to 31 monomers long. Except for the very shortest peptides, an extremely simple energy function is sufficient to discriminate the true native state from more than 10(8) lowest energy conformations that are searched explicitly for each peptide. A high incidence of native-like structures is found within the best few hundred conformations generated by Geocore for each amino acid sequence. Predictions improve when the number of discrete phi/psi choices is increased.     

Male mating strategies under predation risk: do females call the shots?

Many authors have reported that, under elevated risk of predation,male guppies (Poecilia reticulata) alter their behavior fromcourtship to forced copulation (gonopodial thrusts not precededby sigmoid displays). This shift is presumed to benefit thebrightly colored male, whose intense courting activity mightotherwise increase his risk of detection and attack by predators.However, there is some evidence that females engaged in reproductiveactivity with males may be even more vulnerable to predatorsthan the males themselves, which suggests an alternative hypothesis:females in high-risk situations are less receptive to male courtship,and this leads males to change their behavior. We tested thishypothesis by providing either males and females separately,or both sexes concurrently, with information about elevatedpredation risk from a cichlid (Crenicichla sp.). We found thatwhen only females were provided with information about increased risk,males performed fewer courtship displays and fewer thrusts.They did not perform more forced copulations in any treatmentgroup. Nonetheless, our results suggest that the female's perceptionof predation risk can be at least as important as the male'sin changing male mating behavior.     

Determination of the mode of interaction of Mn2+ and Cu2+ with cis-inositol by 13C NMR spectroscopy

Natural abundance ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) was used to study the mode of binding of Mn²⁺ and Cu²⁺ to the cyclitol, cis-inositol. Resonance linewidths and the electron nuclear relaxation rates [(T₁^e)^?1 values] were used to establish that a unique binding site exists for these metal-ions on this cyclitol involving only the three axial hydroxyl groups. This work may aid in the development of new organometallic complexes used as paramagnetic relaxation agents in magnetic resonance imaging research.     

A 13C-methylation study of glycophorin A in intact erythrocytes by 13C-NMR spectroscopy

N-terminal $\text{N}{}^{\mathrm{\alpha }}\text{-[}{}^{13}\text{C]monomethylamino}$ derivatives for the N-terminal serine and leucine residues of glycophorins A^M and A^N, respectively, were obtained by reductively ¹³C-methylating homozygous human erythrocytes (MM, NN). The ¹³C-labeled glycophorins, A^M and A^N, were then isolated. A unique structural state was observed in solution reductively ¹³C-methylated glycophorin A^M that was not observed in glycophorin A^M derived from ¹³C-methylated erythrocytes. We attribute this state to the fact that some of the glycophorin A^M forms a head-to-head dimer when subjected to reductive ¹³C-methylation in aqueous solution. The ¹³C chemical shift data and pH titration data for the N-terminal [¹³C]dimethylamino and [¹³C]monomethylamino groups of glycophorin A^M and A^N derived from reductively ¹³C-methylated erythrocytes were in agreement with the chemical shift and titration data previously obtained for the N-terminal [¹³C]dimethylamino groups of solution reductively ¹³C-methylated glycophorins and related glycopeptides and peptides and N-terminal [¹³C]monomethylamino groups of related glycopeptides and peptides.