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Biomedical subjects

T Ramakrishna

Publications and source records attributed to T Ramakrishna.

At least 37 records · Page 2Linked to original sources
PubMed1996

The role of sexually dimorphic medical preoptic area of the hypothalamus in the sexual behaviour of male and female rats.

The neonatally gonadectomized male rats failed to show typical male clasping of the flanks of the female rat in oestrous stage and also could not achieve intromission and ejaculation when studied at 90 days of age. The replacement of testosterone propionate did not abolish the deficit in sexual behaviour observed. The multiunit electrical activity (MUA) in the medial preoptic area (MPOA) of intact males as well as of oestrous females increased significantly in amplitude and frequency from the low basal levels during mounting, but reverted almost to the basal levels after mounting. The basal MUA in the gonadectomized male rats was of relatively high frequency and amplitude when compared to the intact males and oestrous females, and did not show significant changes during and after mounting. It is suggested that the dimorphic organization of MPOA, developing under the influence of neonatal testosterone, plays a significant role in the male sexual behaviour in adulthood.

Animals↗
PubMed1995

Rapid refolding studies on the chaperone-like alpha-crystallin. Effect of alpha-crystallin on refolding of beta- and gamma-crystallins.

alpha-Crystallin, a multimeric protein present in the eye lens, is shown to have chaperone-like activity in preventing thermally induced aggregation of enzymes and other crystallins. We have studied the rapid refolding of alpha-crystallin, and compared it with other calf eye lens proteins, namely beta- and gamma-crystallins. alpha-Crystallin forms a clear solution upon rapid refolding from 8 M urea. The refolded alpha-crystallin has native-like secondary, tertiary, and quaternary structures as revealed by circular dichroism and fluorescence characteristics as well as gel filtration and sedimentation velocity measurements. On rapid refolding, beta- and gamma-crystallins aggregate and form turbid solutions. The presence of alpha-crystallin in the refolding buffer marginally increases the recovery of beta- and gamma-crystallins in the soluble form. However, unfolding of these crystallins together with alpha-crystallin using 8 M urea and subsequent refolding significantly increases the recovery of these proteins in the soluble form. These results indicate that an intermediate of alpha-crystallin formed during refolding is more effective in preventing the aggregation of beta- and gamma-crystallins. This supports our earlier hypothesis (Raman, B., and Rao, C. M. (1994) J. Biol. Chem. 269, 27264-27268) that the chaperone-like activity of alpha-crystallin is more pronounced in its structurally perturbed state.

Animals↗
PubMed1995

Temperature dependent chaperone-like activity of alpha-crystallin.

Alpha-crystallin, a multimeric protein present in the eye lens, is known to have chaperone-like activity in preventing the aggregation of enzymes and other crystallins. We have studied the chaperone-like activity of this protein towards the aggregation of insulin B chain, induced by reducing the interchain disulphide bond with dithiothreitol. At room temperature, there is no detectable protection (at a 1:1 (w/w) ratio of insulin: alpha-crystallin) against the aggregation of insulin B chain by alpha-crystallin, whereas it completely prevents this aggregation at 40 degrees C. We have monitored the temperature dependence of the protection of aggregation by alpha-crystallin; the protection increases sharply above 30 degrees C and reaches almost 100% by 41 degrees C. Probing the hydrophobic surfaces of alpha-crystallin with the hydrophobic fluorphore 8-anilino-1 naphthalene sulfonate suggests that the hydrophobic surfaces of alpha-crystallin are exposed to a greater extent above 30 degrees C. A complete prevention of the aggregation is achieved at 27.6 degrees C by increasing the concentration of alpha-crystallin by more than 8 fold. Similar temperature dependent chaperone-like activity of alpha-crystallin is observed towards the aggregation of zeta-crystallin, an enzyme crystallin from guinea pig. We have earlier shown that alpha-crystallin exposes hydrophobic surface(s) at temperatures above 30 degrees C. These results support our earlier hypothesis [Raman, B. and Rao, Ch.M. (1994) J. Biol. Chem. 269, 27264-27268] that the chaperone-like activity of alpha-crystallin is more pronounced in its structurally perturbed state.

Animals↗
PubMed1994

Trichloroacetic acid-induced unfolding of bovine pancreatic ribonuclease. Existence of molten globule-like state.

The exposure of ribonuclease A to trichloroacetic acid was earlier shown to alter the conformation of the protein resulting in reduced enzymatic activity (Sagar, A. J., Subbiah, V., and Pandit, M. W. (1989) Biochim. Biophys. Acta 995, 144-150). We have studied the structure and enzymatic activity of ribonuclease A treated with trichloroacetic acid over a wide range of acid concentrations (0-40%). The far ultraviolet circular dichroism spectra of ribonuclease A, on exposure to acid concentrations less than 10%, indicated an exceptionally high degree of chiral structure. Exposure of ribonuclease A to acid concentrations between 10 and 30% resulted in the formation of a molecule with significant chiral structure (conventionally assigned to residual secondary structure) but reduced tertiary structure (characteristics very similar to those of molten globule). Increased binding of the hydrophobic probe 1-anilinonaphthalene-8-sulfonate to the enzyme treated with 15-30% acid, as compared with the untreated or completely unfolded protein, supported the existence of a state having characteristics of molten globule. Reversed phase high performance liquid chromatography corroborated the data obtained by circular dichroism as well as 1-anilino-naphthalene-8-sulfonate-binding studies. Beyond acid concentrations of 30%, the ribonuclease is completely denatured. The trichloroacetic acid-induced unfolding is shown to be completely reversible.

Anilino Naphthalenesulfonates↗
PubMed1994

Refolding of RNAse A at high concentrations: identification of non-native species.

In this paper, we present an analysis of the soluble species formed on refolding of RNase A at various concentrations, in order to characterize these species with respect to structure and activities. Studies were carried out using reverse-phase high-performance liquid chromatography, circular dichroism, chromatography and ultracentrifugation. At all concentrations of protein used, RNase A refolded to the native form, together with formation of non-native species. These non-native species are either misfolded monomers or aggregates; the percentage of such species increases with increasing concentration of enzyme. Such aggregation appears to be a non-random process governed by intermolecular disulfide crosslinking between monomers. These results reaffirm the principle that the information for folding of the protein is encoded in the amino acid sequence itself.

Chromatography, High Pressure Liquid↗
PubMed1994

Effect of pyridoxine deficiency on maturation of neuromotor coordinations.

In the present study the effect of preweaning pyridoxine deficiency indicates that the body weight and brain weight of pyridoxine deficient rats were significantly lower when compared to the control rats. Onset and stabilisation of reflex reactions were also delayed in the pyridoxine deficient rats. Maturation of neuromotor coordination in the vitamin deficient group was significantly slow as compared to the control groups. This suggests that the importance of maternal pyridoxine supplementation cannot be overlooked in pregnant women especially after prolonged use of anovulatory steroids.

Animals↗
PubMed1992

Apparent specificity of bovine seminal ribonucleases can depend on the conditions used for the isolation of substrate.

RNAase SPL, a ribonuclease isolated earlier from bovine seminal plasma, was shown to possess the ability to produce large acid-insoluble fragments of Mg(2+)-containing RNA in a limit digest. The factor which could be responsible for this apparent specificity has been identified as polyvinyl sulphate; it has been shown that polyvinyl sulphate inhibits RNAase SPL at much lower concentrations than required for RNAase A. The earlier results are now reinterpreted based on this effect of polyvinyl sulphate, thus providing a plausible explanation for RNAase SPL's apparent specificity. RNAase SPL has been shown to be a mixture of two ribonucleases, RNAase SPL I and RNAase SPL II. RNAase SPL I is like RNAase A in its activity while RNAase SPL II, the major ribonuclease in seminal plasma, appears to be identical to RNAase BS1.

Amino Acid Sequence↗
PubMed1992

Involvement of active site in self-association of proteins: a case of alpha-chymotrypsin.

The self-association of proteolytic enzymes can be looked upon as an interesting possibility of the manifestation of enzyme-substrate complex. Hence the involvement of active site in such processes is a centre of investigation for many years. In the case of alpha-chymotrypsin, considerable controversy exists with regard to the involvement of active site of the enzyme in its self-association. A historical perspective of the problem and an overview of the available evidence, for and against, is presented and critically analysed. Despite contradicting observations, accumulated evidence indicates that His-57 and Ser-195 at the active site are involved, at least partially, in the self-association; a few other groups such as Tyr-146 and Met-192 are also involved in such processes.

Amino Acid Sequence↗
PubMed1986

Helix-destabilization of deoxyribonucleic acid and poly[d(A-T).d(A-T)] by bovine seminal ribonuclease.

A ribonuclease isolated earlier from bovine seminal plasma by DNA-affinity chromatography (Ramakrishnamurti, T. and Pandit, M.W. (1983) J. Chromatogr. 260, 216-222) has now been shown by thermal denaturation studies to destabilize the double-helical structure of DNA and poly[d(A-T).d(A-T)]. Thermal denaturation profiles of DNA in the presence of the protein are much more complicated due to the denaturation of protein itself in the temperature range over which DNA predominantly melts. The protein shows relatively stronger affinity towards denatured DNA as compared to native DNA. The action of micrococcal nuclease on DNA and its complexes with ribonuclease A and bovine seminal ribonuclease indicates that both of these proteins destabilize the double-helical structure of native DNA and thereby render the DNA more sensitive to the micrococcal nuclease.

Animals↗
PubMed1984

Effect of pyridoxine deficiency on the exploratory behavior of rats.

Malnutrition early in life impairs the development of brain as well as behavior. In the present study the behavioral effects of preweaning pyridoxine deficiency in rats, as reflected by their exploratory score, have been investigated. The results clearly indicated that the body weight of pyridoxine-deficient rats was significantly less when compared to the control rats. Besides this, the sign of maturation of sensory perceptual mechanisms like the first day of eye opening and signs of maturation of neuromotor coordination like the day of supported standing are delayed in vitamin-deficient rats. The open-field activity reflected by the exploratory score was observed to be significantly less in vitamin-deficient rats. In short, considerable effects of prenatal pyridoxine deficiency were observed in the neonatal pups as stunting of growth and in the delayed onset of neuromotor coordination as well as a low level of open-field activity. The importance of maternal pyridoxine supplementation during pregnancy has been emphasized.

Animals↗
PubMed1984

Identity of the ribonuclease from bovine seminal plasma with ribonuclease BS-1, and its sensitivity to polyvinyl sulphate.

A ribonuclease (RNAase BSD) isolated by us earlier from bovine seminal plasma by DNA-affinity chromatography is shown to be homogeneous on polyacrylamide gel electrophoresis, analytical ultracentrifuge and high performance liquid chromatography. From amino acid analysis, high performance liquid chromatography and enzymatic and physicochemical studies, this enzyme is shown to be identical to RNAase BS-1 reported by D'Alessio et al. ((1972) Eur. J. Biochem. 26, 153-161). Immunological studies support this observation. It has also been shown that, as compared to RNAase A, this enzyme is more sensitive to polyvinyl sulphate inhibition.

Amino Acids↗
PubMed1978

Experimental studies on hatching behavior in the chick. IV. Evidence for the role of a noradrenergic mechanism.

In the present experiments we have attempted to determine whether one or more of the biogenic amines are involved in the prehatching and hatching behavior of the chick. Injection of reserpine first induces a depression in ongoing spontaneous motility on day 16 of incubation. Prior to this, reserpine has no apparent effect on embryonic behavior. Reserpine injections on days 17-19 induce a similar behavioral depression that lasts for at least six hours; by 24 hours post-injection the behavior of reserpine-treated embryos is comparable to controls. Injection of reserpine on day 20 (post-pip) delays hatching by about nine hours. Injection of reserpine into the yolk-sac of eggs prior to incubation also delays hatching by eight to nine hours. It is unlikely that the well-known cardiovascular effects of reserpine are involved in the above behavioral results since spinal embryos also exhibit a behavioral depression following reserpine treatment. Biochemical estimation of norepinephrine (NE) in the brain of reserpine-treated embryos suggest that it is release, not depletion, of the catecholamines that is responsible for the behavioral effects. Additional suport for this notion comes from experiments in which 16- or 18-day old embryos were injected with NE, L-dopa or amphetamine. In each case, a behavioral depression similar to that produced by reserpine resulted. Clonidine, a NE agonist induces a depression in certain aspects of embryonic behavior (Types 1 and 2), but also selectively enhances a corrdinated motor pattern (type 3 motility) involved in prehatching behavior (tucking). Clonidine first evokes this behavior pattern one or two days prior to its spontaneous appearance on day 16. After pipping on day 19 or 20 clonidine no longer activates Type 3 behavior, even if injected during the actual hatching process (climax). Since the alpha-adrenergic blocking agent phenoxybenzamine blocks the effect of clonidine on Type 3 tucking behavior, whereas the beta-adrenergic blocker propranolol does not, we suggest that tucking and the attainment of the hatching position are mediated by an alpha-adrenergic mechanism in the brain and/or spinal cord. Furthermore, since clonidine affects the Type 3 behavior associated with tucking, but not the somewhat similar coordinated behavior involved in hatching and emergence from the shell (climax), we propose that this later behavior pattern be given a new name, Type 4 motility.

Amphetamine↗
PubMed1978

Gastric chemoceptive projections to fasciculus solitarius and its dipole field structure.

The gastric branch of the vagus nerve, close to the stomach was stimulated electrically and the evoked potentials recorded from the fasciculus solitarius of frog within the stereotaxic coordinates P 4.1-4.6; L 0.5-0.8 and V 0.3-0.5. A predominantly monophasic negative potential, the amplitude (1.0-3.0 mV) of which rises with increase in stimulus strength up to 6 V, could be recorded. From the velocity of conduction (30 m/sec) it appears that the gastric afferent fibres belong to Group A. The depth-recording resulted in the reversal of the negative sign of the potential at depth beyond 180-200 mu. The significance of the appearance of a positive potential and the cellular configuration of the area of fasciculus is discussed in the context of a possible dipole that might exist in the spatial structure from which the depth-recording has been made.

Animals↗
PubMed1977

Nature and the time course of the effect of CO2 on electroretinogram (ERG) in an arachnid.

Electroretinogram recorded from the median eye of the scorpion, Heterometrus fulvipes before and after exposure to CO2 indicated that the rate of recovery of 'b' wave to pre-CO2 level was slow and delayed as compared to 'a' wave. 'b' wave may therefore have a more central origin than that of 'a' wave, which finds corroboration in the results of the depth recording in this eye with the microelectrode.

Animals↗