Distributed communication and psychosocial performance in simulated space dwelling groups.

The present report describes the development and application of a distributed interactive multi-person simulation in a computer-generated planetary environment as an experimental test bed for modeling the human performance effects of variations in the types of communication modes available, and in the types of stress and incentive conditions underlying the completion of mission goals. The results demonstrated a high degree of interchangeability between communication modes(audio, text) when one mode was not available. Additionally, the addition of time pressure stress to complete tasks resulted in a reduction in performance effectiveness, and these performance reductions were ameliorated via the introduction of positive incentives contingent upon improved performances. The results obtained confirmed that cooperative and productive psychosocial interactions can be maintained between individually isolated and dispersed members of simulated spaceflight crews communicating and problem-solving effectively over extended time intervals without the benefit of one another's physical presence.

The effects of bleaching application time on the dental pulp.

This study evaluated and compared pulpal responses of teeth exposed to a 10 percent carbamide peroxide bleaching gel using short and extended application times. Of 28 subjects, four discontinued use because of thermal sensitivity. For the remaining participants, there was no difference between the pulpal readings recorded before the use of the gel or at any point during the study.

Clinical changes in the gingiva as a result of at-home bleaching.

An investigative study was performed to evaluate changes in gingival health with the application of a 10% carbamide peroxide bleaching gel using exposure times of 2 and 7 hours (overnight). The presence or absence of gingival inflammation was recorded using the Loe and Silness Gingival Index at intervals over a 28-day period. The results showed no statistical significance between the preoperative gingival index scores and those recorded at any point during the study, regardless of exposure time.

Synthetic peptides and ribosomal proteins as substrate for 60S ribosomal protein kinase from yeast cells.

Kinetic studies on the 60S protein kinase were conducted with synthetic peptides and ribosomal proteins as substrate. Peptide RRREEESDDD proved to be the best synthetic substrate for this enzyme. The peptide has a sequence of amino acids which most closely resembles the structure of potential phosphorylation sites in natural substrates, i.e., acidic ribosomal proteins. The superiority of certain kinetic parameters for 60S kinase obtained with the native whole 80S ribosomes over those of the isolated fraction of acidic ribosomal proteins indicates that the affinity of 60S kinase to the specific protein substrate not only depends on the structure of the polypeptide chain around the target amino acid but also on its native structure within the 80S ribosome.

Phosphorylation of acidic ribosomal proteins by ribosome-associated protein kinases of Saccharomyces cerevisiae and Schizosaccharomyces pombe.

Two proteins of 13 kDa and 38 kDa, the components of 60S ribosomal subunits, were identified as phosphorylation substrates for protein kinases tightly associated with S. cerevisiae and Schizosaccharomyces pombe ribosomes. An enzyme with properties of multifunctional casein kinase II was detected in ribosome preparations from both yeast species. In S. cerevisiae another protein kinase with high substrate specificity toward those proteins was also identified. By using isoelectric focusing, the protein band of 13 kDa from S. cerevisiae and S. pombe was resolved respectively into three and four major forms of different charge. The same protein forms were phosphorylated in the in vivo 32P-labelling experiments.

Specific protein kinase from Saccharomyces cerevisiae cells phosphorylating 60S ribosomal proteins.

A protein kinase, specific for 60S ribosomal proteins, has been isolated from Saccharomyces cerevisiae cells, purified to almost homogeneity and characterized. The isolated enzyme is not related to other known protein kinases. Enzyme purification comprised three chromatography steps; DEAE-cellulose, phosphocellulose and heparin-Sepharose. SDS/PAGE analysis of the purified enzyme, indicated a molecular mass of around 71 kDa for the stained single protein band. The specific activity of the protein kinase was directed towards the 60S ribosomal proteins L44, L44', L45 and a 38 kDa protein. All the proteins are phosphorylated only at the serine residues. None of the 40S ribosomal proteins were phosphorylated in the presence of the kinase. For that reason we have named the enzyme the 60S kinase. An analysis of the phosphopeptide maps of acidic ribosomal proteins, phosphorylated at either the 60S kinase or casein kinase II, showed almost identical patterns. Using the immunoblotting technique, the presence of the kinase has been detected in extracts obtained from intensively growing cells. These findings suggest an important role played by the 60S kinase in the regulation of ribosomal activity during protein synthesis.

The 45 kDa and 27 kDa yeast's protein kinases are not immunologically related.

Two yeast casein kinase type-1 species of 45 kDa and 27 kDa (CK1) were purified to apparent homogeneity and used for investigation of their immunological affinity. Antisera against the two kinases were isolated; the antibody against the 45 kDa kinase did not react with the 27 kDa enzyme. The 27 kDa casein kinase was recognized only by its own antibody. The obtained data strongly suggest that the low molecular mass CK-1 is not a proteolytic product of the 45 kDa kinase species.

Effect of gum chewing on plaque accumulation.

The purpose of this investigation was to test the effect of chewing gum sweetened with either sorbitol (LG) or sucrose (SG) on the growth of plaque on tooth enamel surfaces. Nineteen dental students, in a balanced crossover design, chewed the two gums for 5 days without normal oral hygiene practices. The control treatment was a 5-day non-chewing (NG) phase. A period of 9 days was allowed for normal hygiene between test phases. The chewing regimen required 20 minutes of use of one stick of chewing gum immediately after meals or snacks. The average number of sticks chewed was 3.8/day. Pre- and post-treatment plaque scores were recorded by two examiners using a Modified Navy Plaque Index (PLI) from 0 to 9 along each of four surfaces to assess six Ramfjord teeth. Pre-treatment mean PLI scores for the 3 test treatments were, NG = 2.0, LG = 1.9 and SG = 1.9. Post-treatment mean PLI scores were, NG = 3.6, LG = 3.3 and SG = 3.3. ANOVA of pre- and post-treatment scores revealed no significant differences between treatments. Post-treatment scores of the 2 chewing gums were then pooled, independent of sweetener. ANOVA of these data revealed chewing gum (LG + SG = 3.3) to cause significantly less plaque accumulation than no gum (NG = 3.6). In a no oral hygiene environment, plaque accumulation during use of sorbitol chewing gum or sucrose chewing gum was statistically the same. However, chewing gum, irrespective of sweetener, caused significantly less plaque accumulation than no chewing.

Structure and properties of casein kinase-2 from Saccharomyces cerevisiae. A comparison with the liver enzyme.

A type-2 casein kinase (YCK-2), lacking the 25-kDa autophosphorylatable beta subunit characteristic of animal casein kinases-2, has been obtained in a nearly pure form from Saccharomyces cerevisiae and was compared with liver casein kinase-2 (LCK-2). A 22-kDa phosphorylatable protein, copurifying with YCK-2, can be removed by ultracentrifugation at low ionic strength and is shown by several criteria to be unrelated to the beta subunit of LCK-2. The native Mr of YCK-2, deprived of the 22-kDa phosphoprotein, is about 150 000. Limited proteolysis experiments show that YCK-2 included 37-kDa catalytic subunits, which can be converted into still active 35-kDa proteolytic derivatives. These data are consistent with a homotetrameric quaternary structure as opposed to the heterotetrameric subunit composition alpha 2 beta 2 of LCK-2 and other animal casein kinases-2. Although many properties of YCK-2 and LCK-2, including substrate specificity, inhibition by heparin, polyglutamic acid and quercetin and stimulation by polyamines, are similar; their stability under denaturing and dissociating conditions and their response to polybasic peptides are quite different. In particular YCK-2 is more readily denatured than LCK-2 by heating and exposure to urea, sodium dodecylsulphate and deoxycholate while its activity is inhibited by 100-150 mM NaCl, which conversely stimulates LCK-2 activity 2-3-fold. The Km value of the synthetic peptide substrate Ser-(Glu)5 for YCK-2 is not significantly changed by the addition of polylysine. On the contrary the Km value of the same peptide substrate for LCK-2 decreases approximately tenfold upon addition of polylysine, which also prevents the fast autophosphorylation of the kinase at its beta subunit. These data suggest that the beta subunit of animal CK-2 may play a role in determining both the stability of the enzyme and its regulation and that, consequently, the different properties of YCK-2 may be at least in part accounted for by its lack of beta subunits.

Further studies on the quaternary structure of yeast casein kinase II.

Casein kinase type II were isolated by the same procedure, from rat liver, human placenta, Querin carcinoma and yeast, and characterized. The mammalian enzymes were composed of three subunits alpha, alpha' and beta, whereas yeast kinase was composed of two subunits alpha and alpha'. It was shown that the catalytic activity, substrate and phosphate donor specificity, sensitivity to heparin and spermine were the same for all the kinases tested. The results give additional support to the suggestion [1] that the beta subunit is not required for optimal activity and specificity of yeast casein kinase II. The quaternary structure of the yeast enzyme of a molecular weight of approximately 150 000 is proposed as alpha2 alpha'2.

A type-1 casein kinase from yeast phosphorylates both serine and threonine residues of casein. Identification of the phosphorylation sites.

A protein kinase (casein kinase 1A) active on casein and phosvitin but not on histones has been purified to near homogeneity from yeast cytosol and meets most criteria for being considered a type-1 casein kinase: it is a monomeric enzyme exhibiting an Mr of about 27 kDa by sucrose gradient centrifugation: it is not affected by inhibitors of type-2 casein kinases, such as heparin and polyglutamate, and shows negligible affinity for GTP. It also readily phosphorylates the residue Ser-22 of beta-casein located within the sequence -Ser(P)-Ser(P)-Ser(P)-Glu-Glu-Ser22-Ile-Thr-Arg- which is typically affected by casein kinases of the first class. On the other hand, casein kinase 1A displays the unusual property of phosphorylating threonine residue(s) in both whole casein and alpha s1-casein. The threonine residue phosphorylated in alpha s1-casein and accounting for most of the 32P incorporated into this protein by casein kinase 1A has been identified as Thr-49, which occurs in the sequence -Ser(P)-Glu-Ser(P)-Thr(P*)49-Glu-Asp-Gln-, whose two Ser(P) residues are already phosphorylated in the native protein. It is concluded that some type-1 casein kinases can also phosphorylate threonine residues provided they fulfil definite structural requirements, probably an acidic cluster near their N-terminal side.

A minor species of a type I casein kinase from yeast phosphorylating threonine residues of protein substrate.

Protein kinase of Mr 23 000 was isolated from yeast and purified to apparent homogeneity. The enzyme preferentially phosphorylated casein and phosvitin in the presence of ATP as a phosphoryl donor. Its activity was neither affected by cyclic nucleotides nor by heparin. The kinase displayed practically the same substrate specificity as a typical casein kinase I from yeast (Kudlicki, W., Szyszka, R., Palen, E. and Gasior, E. (1980) Biochim. Biophys. Acta 633, 376-385) except that it phosphorylated threonine instead of serine residues in protein substrates.

Phosphorylation of ribosomal proteins during differentiation of Saccharomyces cerevisiae.

Four major phosphoproteins of yeast ribosomes: S2, S6, L44 and L45, were identified in germinating spores. It was found that protein S6 became phosphorylated at an early stage of germination and that only the phosphorylation of this protein responded well to changes in growth conditions of yeast culture. The results obtained give support for the suggested functional role of modification of S6 protein.

A cytoplasmic, cyclic nucleotide-independent casein kinase II from Saccharomyces cerevisiae.

Two molecular forms of casein kinase II (an ATP: protein phosphotransferase, EC 2.7.1.37) from yeast were isolated and characterized. The first form was composed of three polypeptide subunits with molecular weights of 41000, 37000 and 24000. The second form contained two larger polypeptides and lacked an autophosphorylatable 24 kDa subunit. The properties of both enzyme forms were found to be practically the same in respect to the substrate and phosphate donor specificities, kinetics, their sensitivity to heparin, etc. The results obtained strongly indicate that isolated yeast casein kinase II does not necessarily require the smallest subunit for the enzyme activity.

Yeast ribosome core particles deficient in acidic proteins L44 and L45 and their activity in reconstitution experiments.

The yeast ribosome core particles partly depleted of acidic proteins, L44 and L45, were isolated and their activity was examined using a highly purified protein synthesizing system. It was shown that both the phenylalanine polymerization reaction and the elongation factor 2-dependent GTP hydrolysis were stimulated by the addition of the extracted acidic protein fraction. The results obtained clearly indicate a functional role of these proteins in the elongation step of eukaryotic protein synthesis. The essential parameters of ribosome reconstitution experiments are discussed.