Reversible beta-pleated sheet formation of a phosphorylated synthetic tau peptide.

Serine416 of human tau protein is believed to be phosphorylated in Alzheimer neurofibrillary tangles. We synthesized a fragment of tau, consisting of amino acids 408-421 in both non-phosphorylated and serine416-phosphorylated forms. Circular dichroism in a trifluoroethanol-water mixture indicated a beta-turn----beta-pleated sheet conformational transition upon phosphorylation. The beta-structure formation is intermolecular and can be inhibited by addition of Ca2+ ions or a phosphorylated tripeptide, but not with its non-phosphorylated analog. The presence of the phosphorylated tau peptide did not facilitate the formation of beta-pleated sheets of a phosphorylated neurofilament fragment. Multivalent cations induced a conformational transition of this phosphorylated neurofilament peptide, but the effect was less specific than the transition induced in the tau fragment, and it could also be reversed with the competing phosphorylated tripeptide.     

Antipeptide antibody to the insulin-like growth factor-I receptor sequence 1232-1246 inhibits the receptor kinase activity.

To approach the question of why insulin-like growth factor-I (IGF-I) and insulin have different physiological actions, we developed antibodies directed against cytoplasmic regions of the IGF-I receptor exhibiting a low degree of homology with the corresponding sequences of the insulin receptor. We found that an antipeptide antibody directed against the beta-subunit carboxyl-terminal sequence (1232-1246) of the IGF-I receptor significantly reduced the in vitro receptor autophosphorylation. The ability of the synthetic peptide corresponding to the IGF-I receptor sequence 1232-1246 to abolish this inhibitory effect reflects the specific nature of the antibody interaction with the targeted domain in the receptor. Antipeptide antibody to IGF-I receptor sequence 1232-1246 also decreased receptor phosphorylation activity toward the exogenous substrate poly(Glu/Tyr). The reduction in poly(Glu/Tyr) phosphorylation was seen even when the antibody was incubated with a receptor previously activated and phosphorylated. Therefore, the inhibitory action on substrate phosphorylation is likely to be unrelated to the antibody reduction of receptor autophosphorylation but rather results from a global decrease in receptor enzymatic activity. The effect of the antipeptide antibody on receptor tyrosine kinase cannot be accounted for by a lowering of the receptor Km for ATP or of its affinity for the substrate poly(Glu/Tyr). Moreover, the interaction of the antibody with the receptor had no repercussion on the ligand binding site as shown by the unaltered IGF-I binding. Taken together our data suggest that the beta-subunit carboxyl-terminal domain of the IGF-I receptor plays a key role in regulating its kinase activity and that the particular sequence recognized by our antipeptide antibody could be involved in negative regulation of receptor functioning.     

Effects of tranquilizing agents on bioelectrical activity of the rat brain]

The action of diazepam, meprobamate, trioxazine and mexidol on bioelectrical activity of sensorimotor cortex and dorsal hippocamp of the left and right hemisphere of the brain in conscious rat in free behavior has been studied. All the drugs produced a decline in the frequency of the dominant peak of EEG power spectra. Diazepam and meprobamate increased beta-activity. It is concluded that the decreased frequency may be due to an anxiolytic effect of the tranquilizers, whereas high beta-activity is related to muscle relaxant effect of some drugs.     

Seasonal and circadian fluctuations in blood biochemical indicators in mice in natural conditions and exposed to constant light]

The fluctuations of activity of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and those of the levels of protein, glucose, cholesterol, bilirubin, creatinine, blood urea nitrogen, K+, Cl-, Na+ in blood plasma of mice in natural conditions (NC) and exposed to constant light (CL) were studied in different seasons of the year (in January, April, July, October) on days 18, 24, 6 (at 12 o'clock). Most indices both in NC and CL animals had seasonal rhythm similar for each of them. This proves a primary effect of environmental geoclimatic factors of formation of circadian periodicals as compared to desynchronization in constant light revealed by Kosinor analysis in winter (acrophase from 14.16 till 16.32 o'clock) and autumn (acrophase from 23.03 til 4.40 o'clock). During the same seasons one can observe the maximum desynchronization influences of constant light, which leads to abrupt falling (to the 10-fold and more) of the fluctuations amplitude and in some cases to stabilization of circadian rhythm.     

Interaction of GABA and volatile anesthetics in the nematode Caenorhabditis elegans

The authors tested whether mutant strains of Caenorhabditis elegans with altered sensitivity to volatile anesthetics have altered responses to GABA or GABA-agonists. They determined the ED50s of the wild-type strain N2 and two mutant strains of C. elegans to a GABA-mimetic ivermectin (IVM) and to GABA. unc-79, a strain with increased sensitivity to halothane, was more sensitive than N2 to IVM and GABA. unc-9, a strain that suppresses the increased sensitivity of unc-79 to halothane, was less sensitive than N2 to IVM and GABA. The authors also tested whether doses of GABA or IVM and volatile anesthetics were additive in their effects on C. elegans. Halothane (2.1%) did not shift the ED50 of IVM, but was antagonistic to GABA. Enflurane (4%) was antagonistic to both IVM and GABA. However, ED50s of halothane and enflurane were unchanged in the presence of IVM (35 nM) or GABA (150 mM). The authors conclude that GABA by itself does not appear to mediate halothane or enflurane sensitivity in C. elegans.     

Characteristics of the interaction between 2-alkylmalonates and the substrate-binding site of the dicarboxylate carrier of rat liver mitochondria

The effect of thirteen synthetic 2-n-alkyl derivatives of malonic acid on the rate of the mitochondrial succinate oxidase reaction controlled by the dicarboxylate carrier, was studied. These compounds were shown to act as competitive inhibitors of succinate transport and could interact with the carrier according to the 1:1 stoichiometry. The affinity of the inhibitor for the carrier increased in parallel with the increase in the alkyl residue length. This dependence was impaired only in the case of pentyl-, hexyl- and heptylmalonates having close values of inhibition constants. The data obtained suggest that the polar site and two hydrophobic regions are located in the vicinity of the carrier active site. The possible organization of the carrier substrate-binding site is discussed.     

The effect of estradiol on the initiation of phosphoinositide catabolism in rat brain synaptic membranes

The in vivo effect of estradiol on phosphoinositide catabolism initiation provoked by K(+)-depolarization of rat brain synaptosomal membranes was studied. The decreased yield of diacylglyceride was revealed on the 5th sec of initiation. It was found that estradiol markedly increases the phospholipid content, particularly that of phosphatidylinositol, in synaptosomal membranes but causes a simultaneous decrease of the neutral lipid content. The activity of phosphatidylinositol-specific phospholipase C is significantly decreased thereby. It was concluded that the effect of the steroid hormone on the genome provides for a functional status of membrane structures which slightly impedes the processes mediated by phosphoinositides.     

A submerged-coil heating apparatus for investigating thermal inactivation of micro-organisms

A novel apparatus has been designed for the investigation of the thermal inactivation of micro-organisms over the temperature range 20–90C. It comprises a stainless steel coil fully submerged in a thermostatically-controlled water bath which allows very rapid temperature equilibration of microbial suspensions. Automated repeat sampling is possible at short time intervals (variable between 6 and 999 s) by means of an electronically controlled displacement mechanism. Validation of the apparatus performance and typical death curves are described.