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Biomedical subjects

G Sander

Publications and source records attributed to G Sander.

At least 55 records · Page 3Linked to original sources
PubMed1979

Cation-induced regulatory mechanism of GTPase activity dependent on polypeptide initiation factor 2.

Initiation factor IF-2 ribosome dependent GTP hydrolysis (uncoupled GTPase) presents a bell-shaped pH profile which is shifted by changes in ionic strength. At low ionic strength (I = 25 mM) the maximal hydrolytic activity occurs at pH 7.5; when the ionic strength is increased the pH optimum of the reaction is shifted toward more acidic values. Such behavior can be satisfactorily explained as the effect of an electrostatic potential developed by a neighboring polyanion, presumably RNA, on the catalytic site. The addition of fMet-tRNAfMet or AcPhe-tRNAPhe and messenger RNA (coupled GTPase) changes the ionic strength--pH characteristics of the reaction. Thus there is an effect, direct or indirect, of components located at the ribosomal P site. Investigation of the effect of neighboring polyanions on the catalytic activity of the factor-dependent ribosomal GTPases can be seen to provide information about their functional significance that is complementary to that gained from direct structural studies.

Escherichia coli↗
PubMed1979

Relationships between the late component of the contingent negative variation and the bereitschaftspotential.

The purpose of this study was to determine whether the late component of the contingent negative variation (CNV) in a S1-S2-respond paradigm shares critical features with the Bereitschaftspotential (BP) prior to self-paced voluntary movements. In a group of 8 subjects, the late CNV and the BP exhibited: (a) similar effects of response speed variation, (b) corresponding influences of subjective factors, and (c) a similar scalp distribution with the exception that the BP was much more lateralized. In contrast, no such relationships were found between early CNV and BP.

Brain↗
PubMed1978

Chlamydomonas flagellar mutants lacking radial spokes and central tubules. Structure, composition, and function of specific axonemal components.

The fine structure, protein composition, and roles in flagellar movement of specific axonemal components were studied in wild-type Chlamydomonas and paralyzed mutants pf-14, pf-15A, and pf-19. Electron microscope examination of the isolated axoneme of pf-14 showed that it lacks the radial spokes but is otherwise structurally normal. Comparison of isolated axonemes of wild type and pf-14 by sodium dodecyl sulfate-acrylamide gel electrophoresis indicated that the mutant is missing a protein of 118,000 mol wt; this protein is apparently a major component of the spokes. Pf-15A and pf-19 lack the central tubules and sheath; axonemes of these mutants are missing three high molecular weight proteins which are probably components of the central tubule-central sheath complex. Under conditions where wild-type axonemes reactivated, axonemes of the three mutants remained intact but did not form bends. However, mutant and wild-type axonemes underwent identical adenosine triphosphate-induced disintegration after treatment with trypsin; the dynein arms of the mutants are therefore capable of generating interdoublet shearing forces. These findings indicated that both the radial spokes and the central tubule-central sheath complex are essential for conversion of interdoublet sliding into axonemal bending. Moreover, because axonemes of pf-14 remained intact under reactivating conditions, the nexin links alone are sufficient to limit the amount of interdoublet sliding that occurs. The axial periodicities of the central sheath, dynein arms, radial spokes, and nexin links of Chlamydomonas were determined by electron microscopy using the lattice-spacing of crystalline catalase as an internal standard. Some new ultrastructural details of the components are described.

Adenosine Triphosphate↗
PubMed1977

Evidence for a functional role of RNA in centrioles.

Basal bodies, purified from Chlamydomonas and Tetrahymena, were exposed to various enzymatic treatments and then assayed for their ability to nucleate aster formation upon injection into eggs of Xenopus laevis. Untreated basal bodies injected into frog eggs act as centrioles and induce the formation of asters. The aster-inducing activity of basal bodies was eliminated by treatment with proteolytic enzymes and ribonucleases. Aster-inducing activity was not affected by DNAse and a number of other enzymes. The effect of proteolytic digestion on aster-inducing activity appeared to be directly correlated with the degree of structural damage to the basal body. Low concentrations of pancreatic ribonuclease A, ribonuclease T1, and S1 nuclease also completely abolished aster-inducing activity, although these enzymes had no effect on basal body structure. Ribonuclease-treated basal bodies remained capable of supporting microtubule elongation in vitro. Preliminary evidence indicates that basal bodies from Chlamydomonas and Tetrahymena contain about 5 x 10(-16) g of RNA which co-band with basal bodies and aster-inducing activity by equilibrium density gradient sedimentation. We conclude first, that centrioles contain RNA which is required for initiation of aster formation, and second, that the centriole activity or ability to assemble a mitotic aster is separable from the basal body activity, or ability to serve directly as a template for microtubule growth.

Animals↗
PubMed1977

[Tooth mobility in relation to the stress on functional facetes].

By means of inductive motion recorders not in contact with the teeth, tooth movements in buccal and lingual directions were recorded with load being exerted on the different individual functional facets. When loading the retrusion facets the maxillary tooth is displaced lingually and the mandibular tooth buccally. This is significant for grinding-in.

Bruxism↗
PubMed1976

Activity of the 30-S CsCl core in elongation-factor-dependent GTP hydrolysis.

The activity of a 30-S CsCl core lacking proteins S1, S2, S3, S5, S9, S10, S14, S20 and S21 has been studied in the ribosome-dependent FTPase reactions in the presence of the 50-S subunit with and without methanol. Without methanol, the 30-S CsCl core was unable to sustain GTPase activity dependent on elongation factor G (EF-G), while it was only slightly active in the presence of elongation factor T (EF-T). With EF-T, addition of methanol induced in the presence of either 30-S subunits or 30-S CsCl cores an activity which was more than 10-fold higher than that observed with the 30-S subunit in the absence of methanol. Methanol lowered the Mg2+ optimum of the EF-T-dependent GTPase reaction from approximately 20 mM to approximately 10 mM. In the absence of methanol the EF-G-dependent (GTPase reaction at low concentration of monovalent cations depends on the 50-S subunit alone (30-S-uncoupled EF-G GTPase). Addition of the intact 30-S subunit but not of its CsCl core abolished inhibition of the 30-S-uncoupled EF-G-GTPase by NH4+. The 30-S CsCl core caused the same effect as the 30-S subunit when methanol was present. 30-S-uncoupled EF-G GTPase activity was lower than the GTPase activity dependent on 30-S plus 50-S subunits at [EF-G]/[50-S] below 5 but was considerably higher in the presence of a large excess of EF-G. In the presence of methanol the 30-S CsCl core behaved similarly to the 30-S subunit. Our results indicate that the action of the 30-S subunit in elongation-factor-dependent GTPases is supported by structural features that are preserved in the 30-S CsCl core. The 30-S split proteins are therefore not essential for EF-G and EF-T activities in the hydrolysis of GTP. With EF-T, in all conditions tested association of the ribosomal subunits appeared to accompany GTPase activity. Association seems also to be a prerequisite of the EF-G GTPase activity that depends on both ribosomal subunits.

Ammonia↗
PubMed1975

A comparative study of the 50S ribosomal subunit and several 50S subparticles in EF-T-and EF-G-dependent activities.

A series of ribosomal subparticles derived from the 50S subunit has been studied and compared in EF-T- and EF-G-dependent reactions. Three different 50S cores were prepared by CsC1 isophycnic centrifugation and one by NH(4)Cl-ethanol extractionm the 50S CsCl core a had lost proteins L1, L7, L8, L10, L12, L16, L25, L33, and some L6 and L11. The 50S CsCl core b additionally lacked protein L6, and 50S CsCl core c also lacked protein L5, L15, L18, L27, L28, L30, and most of L9, L14, L19, and L21. The 50S NH(4)Cl-ethanol core had lost up to 90 percent of proteins L7, L12 and 30-60 percent of proteins L8, L10, and L29. The 50S CsCl core a had much reduced activity in EF-G and none in EF-T GTPase reactions while 50S CsCl cores b and c were inactive. Addition of proteins L7, L12 restored the activity for both the EF-T- and EF-G-dependent GTPase with all of the three 50S CsCl cores, increasing stepwise from core c to core a; The 50S NH(4)Cl-ethanol core was partially active in the EF-G GTPase over the 2-30 mM MG-2+ range tested, while EF-T only showed some activity inthe upper portion of this range...

Bacterial Proteins↗