Degradation properties of co-continuous calcium-phosphate-polyester composites

Co-continuous composites consisting of a porous calcium phosphate matrix (hydroxyapatite, HA, or β-tricalcium phosphate, TCP) filled with poly(D,L-lactide) (PDLLA) were produced with two different methods: in situ polymerization of D,L-lactide monomer inside the matrix, or infiltration of the matrix with molten polymer. The influence of the calcium phosphate matrix as well as the manufacturing method on the degradation were investigated with accelerated in vitro studies at 42 °C in pH 7.4 phosphate-buffered saline (PBS), with some controls at 37 °C. The results show that samples produced with the infiltration method had higher initial molecular weights leading to a later onset of mass loss. Heterogenous polymer degradation was still present in the composites, as indicated by molecular weight distributions and glass transition temperature measurements. The calcium phosphate matrix delayed degradation, with evidence from X-ray microtomography suggesting that the polymer degrades more slowly in proximity to the matrix.     

Probing the stability and mechanism for folding of the GrpE1-112 tetrameric deletion mutant of the GrpE protein from E. coli

Insight into the stability and folding of oligomeric proteins is essential to the understanding of protein folding, especially since the majority of proteins found in nature are oligomeric. A deletion mutant of the GrpE protein from Escherichia coli, that contains the first 112 residues (GrpE1-112) of 197 total, is an oligomeric protein forming a tetrameric structure. A four-helix bundle structure is formed via the interaction of an α-helix (22 amino acids in length) from each monomer. Using both thermal and chemical (urea) denaturation studies, the GrpE1-112 protein has rather low stability with a T(m) of unfolding of 37 °C, a C(m) (urea) of 1.3M, and a ΔG(unfolding) of 8.4 kJ mol(-1). Investigation into the folding pathway using circular dichroism (CD) stopped-flow revealed a two step process with a fast first phase (k(refolding)=8.0 × 10(6)s(-1)M(-1)) forming a multimeric intermediate that possesses significant α-helical content followed by a slow, first order, step forming the folded tetramer.     

This Examined Life: The Upside of Self-Knowledge for Interpersonal Relationships

Although self-knowledge is an unquestioned good in many philosophical traditions, testing this assumption scientifically has posed a challenge because of the difficulty of measuring individual differences in self-knowledge. In this study, we used a novel, naturalistic, and objective criterion to determine individuals’ degree of self-knowledge. Specifically, self-knowledge was measured as the congruence between people’s beliefs about how they typically behave and their actual behavior as measured with unobtrusive audio recordings from daily life. We found that this measure of self-knowledge was positively correlated with informants’ perceptions of relationship quality. These results suggest that self-knowledge is interpersonally advantageous. Given the importance of relationships for our social species, self-knowledge could have great social value that has heretofore been overlooked.     

DnaJ dramatically stimulates ATP hydrolysis by DnaK: insight into targeting of Hsp70 proteins to polypeptide substrates

Most, if not all, of the cellular functions of Hsp70 proteins require the assistance of a DnaJ homologue, which accelerates the weak intrinsic ATPase activity of Hsp70 and serves as a specificity factor by binding and targeting specific polypeptide substrates for Hsp70 action. We have used pre-steady-state kinetics to investigate the interaction of the Escherichia coli DnaJ and DnaK proteins, and the effects of DnaJ on the ATPase reaction of DnaK. DnaJ accelerates hydrolysis of ATP by DnaK to such an extent that ATP binding by DnaK becomes rate-limiting for hydrolysis. At high concentrations of DnaK under single-turnover conditions, the rate-limiting step is a first-order process, apparently a change of DnaK conformation, that accompanies ATP binding and proceeds at 12-15 min-1 at 25 degrees C and 1-1.5 min-1 at 5 degrees C. By prebinding ATP to DnaK and subsequently adding DnaJ, the effects of this slow step may be bypassed, and the maximal rate-enhancement of DnaJ on the hydrolysis step is approximately 15 000-fold at 5 degrees C. The interaction of DnaJ with DnaK.ATP is likely a rapid equilibrium relative to ATP hydrolysis, and is relatively weak, with a KD of approximately 20 microM at 5 degrees C, and weaker still at 25 degrees C. In the presence of saturating DnaJ, the maximal rate of ATP hydrolysis by DnaK is similar to previously reported rates for peptide release from DnaK.ATP. This suggests that when DnaK encounters a DnaJ-bound polypeptide or protein complex, a significant fraction of such events result in ATP hydrolysis by DnaK and concomitant capture of the polypeptide substrate in a tight complex with DnaK.ADP. Furthermore, a broadly applicable kinetic mechanism for DnaJ-mediated specificity of Hsp70 action arises from these observations, in which the specificity arises largely from the acceleration of the hydrolysis step itself, rather than by DnaJ-dependent modulation of the affinity of Hsp70 for substrate polypeptides.     

Central nervous system effects of caffeine and adenosine on fatigue

Caffeine ingestion can delay fatigue during exercise, but the mechanisms remain elusive. This study was designed to test the hypothesis that blockade of central nervous system (CNS) adenosine receptors may explain the beneficial effect of caffeine on fatigue. Initial experiments were done to confirm an effect of CNS caffeine and/or the adenosine A(1)/A(2) receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) on spontaneous locomotor activity. Thirty minutes before measurement of spontaneous activity or treadmill running, male rats received caffeine, NECA, caffeine plus NECA, or vehicle during four sessions separated by approximately 1 wk. CNS caffeine and NECA (intracerebroventricular) were associated with increased and decreased spontaneous activity, respectively, but caffeine plus NECA did not block the reduction induced by NECA. CNS caffeine also increased run time to fatigue by 60% and NECA reduced it by 68% vs. vehicle. However, unlike the effects on spontaneous activity, pretreatment with caffeine was effective in blocking the decrease in run time by NECA. No differences were found after peripheral (intraperitoneal) drug administration. Results suggest that caffeine can delay fatigue through CNS mechanisms, at least in part by blocking adenosine receptors.     

Glass-forming tendency and stability of the amorphous state in the aqueous solutions of linear polyalcohols with four carbons. I. Binary systems water-polyalcohol

All the aqueous solutions of linear saturated polyalcohols with four carbons have been investigated at low temperature. Only ice has been observed in the solutions of 1,3-butanediol and 1,2,3- and 1,2,4-butanetriol. For same solute concentration, the glass-forming tendency on cooling is highest with 2,3-butanediol, where it is comparable to that with 1,2-propanediol, the best solute reported to date. However, the quantity of ice and hydrate crystallized is particularly high on slow cooling or on subsequent rewarming. The highest stability of the amorphous state is observed on rewarming the 1,2-butanediol and 1,3-butanediol solutions. With respect to this property, these compounds come just after 1,2-propanediol and before all the other compounds studied so far. They are followed by dimethylsulfoxide and 1,2,3-butanetriol. The glass-forming tendency of the 1,3-butanediol solutions is also very high; it is third only to that of 1,2-propanediol and 2,3-butanediol. The glass-forming tendency is a little smaller with 1,2-butanediol, but it is cubic instead of ordinary hexagonal ice which crystallizes on cooling rapidly with 35% 1,2-butanediol. Cubic ice is thought to be innocuous. A gigantic glass transition is observed with 45% of this strange solute. 1,4-Butanediol, 45% also favors cubic ice greatly. Therefore, 1,2- and 1,3-butanediol with comparable physical properties are perhaps as interesting as 1,2-propanediol for cryopreservation of cells or organs by complete vitrification. Together with 1,2-propanediol, 1,2- and 1,3-butanetriol, 1,2,3-butanetriol, and perhaps 2,3-butanediol provide an interesting battery of solutions for cryopreservation by vitrification.