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R Mazumder

Publications and source records attributed to R Mazumder.

At least 37 records · Page 2Linked to original sources
PubMed1976

Role of GTP in eukaryotic polypeptide-chain initiation. Purification and properties of a factor from Artemia salina embryos which interacts with initiator transfer RNA and guanine nucleotides.

1. A factor, which makes a ternary complex with GTP and eukaryotic initiator tRNA (Met-tRNAi), has been purified 100-fold from developed cysts of Artemia salina. Some of the properties of the purified factor have been studied. 2. Mg2+ appears to inhibit ternary complex formation. 3. Little or no ternary complex is formed when 5 muM GTP is replaced by an identical concentration of UTP, CTP or ATP. The analog, guanosine 5'-(beta, gamma-imino)triphosphate [GMP-P(NHP)] seems to be a much better substitute for GTP than guanosine 5'-(beta, gamma-methylene)triphosphate [GMP-P(CH2)P]. Since GMP-P(NH)P is as effective as GTP in ternary complex formation, it would appear that GTP plays the role of an allosteric effector in this step of eukaryotic polypeptide chain initiation. 4. GDP inhibits both the rate and extent of ternary complex formation. The inhibition is largely reversed by adding a 5-fold molar excess of GTP over GDP. DGDP is slightly less inhibitory than GDP. UDP and CDP are much less inhibitory than GDP and very little inhibition is obtained with ADP. 5. The preformed ternary complex is rapidly and completely destroyed in the presence of N-ethylmaleimide. The results suggest that free--SH groups of the factor may be essential for maintaining the integrity of the ternary complex.

Animals↗
PubMed1975

Sites of action of fusidic acid in eukaryotes. Inhibition by fusidic acid of a ribosome-independent GTPase from Artemia salina embryos.

1. A ribosome-independent GTPase activity has been isolated from the high-speed supernatant fraction of Artemia salina embryos, and some of its properties have been studied. This activity is inhibited by fusidic acid, an antibiotic generally thought to inhibit only EF-2 in eukaryotes. However, several lines of evidence indicate that the GTPase activity, described here, is distinct from EF-2. The results suggest, therefore, that the inhibitory effect of fusidic acid in eukaryotic systems is not restricted to EF-2 (and ribosome)-dependent functions only. 2. The results of other experiments have revealed that, despite its ability to inhibit the GTPase activity mentioned above, fusidic acid is not a non-specific inhibitor of all ribosome-independent GTPase and ATPase activities present in eukaryotic cells.

Adenosine Triphosphatases↗
PubMed1973

Effect of thiostrepton on recycling of Escherichia coli initiation factor 2.

The recycling of initiation factor 2, which requires both GTP and the 50S subunit and involves GTP hydrolysis, appears to be blocked by thiostrepton. However, this antibiotic has little or no effect on the AUG-directed ribosomal binding promoted by initiation factor 2 of fMet-tRNA under conditions that do not permit optimal recycling of the factor. Evidence is presented suggesting that the 50S ribosomal proteins L7 or L12, which are required for the function of the chain elongation factors Tu and G and the accompanying hydrolysis of GTP, are also involved in recycling of initiation factor 2. Although both 5'-guanylylmethylene diphosphonate and thiostrepton seem to block recycling of initiation factor 2, fMet-tRNA bound to the ribosomes in the presence of GTP and thiostrepton can react with puromycin, whereas that bound in the presence of 5'-guanylylmethylene diphosphonate and the antibiotic cannot. It is proposed that initiation factor 2 may interact with two nonidentical ribosomal sites during polypeptide chain initiation.

Anti-Bacterial Agents↗
PubMed1972

Initiation factor 2-dependent ribosomal binding of N-formylmethionyl-transfer RNA without added guanosine triphosphate.

Evidence is presented that suggests that GTP (or 5'-guanylylmethylene diphosphonate) is not essential for either formation of an AUG-directed, initiation factor IF-2-dependent initiation complex on the 30S subunit or for positioning of fMet-tRNA on the peptidyl site. However, recycling of limiting amounts of IF-2 requires both GTP and the 50S subunit. The formation of the complex IF-2-30S as an intermediate in polypeptidechain initiation is suggested.

Binding Sites↗
PubMed1969

Polypeptide chain initiation in E. coli: isolation of homogeneous initiation factor E2 and its relation to ribosomal proteins.

Previous work has shown that F(2), one of several ribosomal factors involved in polypeptide chain initiation, functions in the binding of formylmethionyl-transfer RNA (fMet approximately tRNA(f)) to a messenger RNA-ribosome complex. F(2) was isolated from 1.0 M ammonium chloride washes of E. coli Q13 ribosomes as a protein homogeneous on polyacrylamide gel electrophoresis at both pH 4.5 and 7.8. Its molecular weight is approximately 80,000. Comparison of electrophoretic patterns of ribosomal proteins from NH(4)Cl-washed and unwashed ribosomes and F(2), at pH 4.5, shows that F(2) corresponds to the slowest-moving component of the proteins derived from unwashed ribosomes. This component is missing from the NH(4)Cl-washed ribosomes. The activity of F(2) is stimulated by two additional factors, initiation factor F(1) and a factor(s) present in a narrow ammonium sulfate fraction of the ribosomal NH(4)Cl wash. The nature of the latter is unknown.

Ammonium Chloride↗
PubMed1969

Polypeptide chain initiation in E. coli: sulfhydryl groups and the function of initiation factor F2.

The activity of the chain initiation factor F(2) in promoting the messenger-dependent binding of formylmethionyl-transfer RNA (fMet approximately tRNA(f)) to purified E. coli ribosomes is inhibited by sulfhydryl-binding reagents, such as N-ethylmaleimide or p-hydroxymercuribenzoate, but prior incubation with guanosine triphosphate (GTP) or with ribosomes largely prevents this inhibition. The effect of GTP suggests that it forms a complex with F(2) whereby "active" sulfhydryl groups become sheltered. Experiments on the time course of the binding reaction, with and without preincubation of F(2) with GTP, and gel filtration experiments with (3)H-labeled GTP lend support to this suggestion.

Benzoates↗
PubMed1969

Polypeptide chain initiation in E. coli: studies on the function of initiation factor F1.

The requirement of initiation factors F(1) (highly purified) and F(2) (electrophoretically homogeneous) for ribosomal binding of N-formylmethionyl transfer RNA (fMet approximately tRNA) at low Mg(2+) concentration (3.5 mM), with the trinucleoside diphosphate ApUpG as messenger, was studied under various experimental conditions with 30S + 50S ribosomes and with 30S subunits alone. The results were qualitatively the same in both cases but the amount of binding was two to three times higher when both 30S and 50S subunits were present. Although there was a virtually absolute requirement for F(2) in all cases, considerable binding occurred at 0 degrees in the absence of added F(1). F(1) addition stimulated binding up to twofold under these conditions. However, at 25 degrees , the temperature at which the reaction is usually carried out, there was very little binding with F(2) alone and addition of F(1) stimulated the reaction five- to sixfold. Contrary to current belief, the GTP analog 5'-guanylyldiphosphonate (GMP-PCP) cannot replace GTP in the binding reaction. In particular, there was but little stimulation of binding (about 1.5-fold) by addition of F(1) to F(2)-containing samples when GMP-PCP was used. In marked contrast, binding was stimulated up to sevenfold by addition of F(1) when GTP was substituted for the analog. Under these conditions, there was an ApUpG and F(1)-dependent hydrolysis of GTP. This is observable with 30S subunits alone and can hardly be related to the occurrence of translocation. The results may be interpreted to mean that a complex relatively stable at 0 degrees , but less stable at 25 degrees , is formed upon addition of F(2) alone. Conversion of the less stable to the more stable form of complex is made possible by addition of F(1). This is accompanied or mediated by cleavage of GTP.

Bacterial Proteins↗
PubMedDate not supplied

Spermatogenesis in rat: effect of L-tryptophan loading.

The present experiment was designed to assess the role of enhanced central 5-HT level on testicular steroidogenesis and spermatogenesis of rat. L-tryptophan, a precursor in the synthesis of 5-HT in brain, was injected in male rats on a short-term (7-days) and a long-term (21-days) basis. The short-term treatment had no effect on the spermatogenic pattern (Stage - VII of the cycle of the seminiferous epithelium), while the long-term treatment showed a degenerative change (reduced count of the germ cells). Both modes of treatment reduced the activity of testicular delta 5-3 beta-HSD without affecting NADH2-linked Diaphorase activity. Histological study of the Leydig cells' nuclear area also revealed a marked reduction after both the modes of treatment. Human chorionic gonadotropin supplementation in the long-term treatment restored the spermatogenesis, delta 5-3 beta-HSD activity and Leydig cells' nuclear area towards the vehicle treated control. The inhibition of spermatogenesis and steroidogenesis reflects a decrease in the pituitary gonadotropin release under the influence of enhanced 5-HT synthesis in brain, after L-tryptophan loading.

3-Hydroxysteroid Dehydrogenases↗
PubMedDate not supplied

Spermatogenesis of rat: effect of central norepinephrine synthesis inhibition by diethyldithiocarbamate.

Spermatogenesis and steroidogenesis of male Wistar rats under the influence of a decreased central NE level was studied. Inhibition of NE synthesis was produced by chronic injection (7 days) of DDC, a Dopamine hydroxylase blocker, which decreased brain NE, increased brain DA without significantly affecting brain 5-HT. Rats were sacrificed on the day after cessation of treatment (8th day) and after an interval of 13 days following the cessation of treatment (21st day). The time interval of 13 days is equivalent to one cycle of the seminiferous epithelium in Wistar strain rats. A degenerative change (reduced spermatid count) in the spermatogenic pattern at stage-VII of the cycle of the seminiferous epithelium was observed in the rats sacrificed on the 8th day, the degeneration being much greater in the rats sacrificed on the 21st day. Rats sacrificed on the day after cessation of DDC treatment revealed an inhibition of plasma testosterone level. Such change was not observed in the rats sacrificed after the interval of 13 days following DDC treatment. Human chorionic gonadotropin supplementation in the rats sacrificed on the 21st day partially restored the spermatogenesis towards the vehicle treated control. The inhibition of spermatogenesis and steroidogenesis reflects a decrease in the pituitary gonadotropin secretion under the influence of a decreased NE synthesis in brain, following chronic treatment of DDC.

Animals↗