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Biomedical subjects

N Kumar

Publications and source records attributed to N Kumar.

At least 397 records · Page 22Linked to original sources
PubMed1984

Anterior radial keratotomy experience in 600 cases of myopia.

Surgical results of anterior radial keratotomy in 1,200 eyes are presented. Of the eyes, 55% had an unaided visual acuity of 6/9 or better six months after surgery. An average of 1.90 D of myopia was corrected in these cases. It takes six weeks for the refraction to stabilize and to know the final success of surgery. There was no statistically significant influence of age or sex or preoperative refractive error on the amount of surgically induced change in refraction. The extent of myopia corrected is directly proportional to the change induced in the radius of curvature. The operative and postoperative complications were minimal and did not endanger vision.

Adolescent↗
PubMed1982

Aggregation and calcium-induced fusion of phosphatidylcholine vesicle-tubulin complexes.

Insertion of tubulin into the bilayer of dipalmitoyl phosphatidylcholine vesicles at the phase transition results in the formation of stable vesicle-tubulin complexes (Klausner, R. D., Kumar, N., Weinstein, J. N., Blumenthal, R., and Flavin, M. (1981) J. Biol. Chem. 256, 5879-5885). These complexes aggregated when maintained below phase transition for 10-20 min. Addition of millimolar concentrations of Ca2+, Mn2+, Zn2+, and Co2+, but not Mg2+, caused the vesicle-tubulin complexes to fuse into larger structures as shown by (a) electron microscopy, (b) increased trapped volume, and (c) changes ion resonance energy transfer between two fluorescent lipid probes incorporated into the same vesicle. There was no loss of internal aqueous contents from the vesicle-tubulin complexes during Ca2+-induced fusion. Anti-tubulin drugs had no effect on the aggregation or fusion, and vesicle-bound tubulin did not associate with microtubules when tubulin was assembled in vitro. Trypsin-treated vesicle-tubulin complexes were incapable of supporting Ca2+-induced fusion. This system provides a model for Ca2+-induced and protein-mediated nonleaky fusion of uncharged lipid bilayers.

Animals↗
PubMed1982

Gel filtration in 6 M guanidine hydrochloride of the alpha-subunit (and its fragments) of the receptor for immunoglobulin E.

The mol. wts of the alpha-chain of the receptor for immunoglobulin E and several of its enzyme-cleaved fragments have been evaluated by gel filtration on Sepharose 6B in 6 M guanidine HCl. The mol. wt of alpha-chains treated with endoglycosidase was 30% less than that of untreated alpha-chains. alpha-Chains digested with papain eluted in a single peak with a mol. wt approximately one-half of that of undigested alpha-chains. The results support the proposal that papain cleaves alpha-chains into two fragments of similar size [Goetze et al. (1981) Biochemistry 20, 6341-6349].

Chromatography, Gel↗
PubMed1982

Modulation of some parameters of assembly of microtubules in vitro by tyrosinolation of tubulin.

Using tyrosinolated and detyrosinolated tubulins, we have compared several parameters of microtubule assembly in vitro. Rates and extents of polymerization were the same under all conditions, but microtubules assembled from detyrosinolated tubulin in the presence of crude microtubule-associated proteins (MAPs) or subsaturating MAP-2 contained a smaller proportion of the MAPs. Preliminary results indicate that this may be a function of the phosphorylation state of MAP-2. Tyrosinolated tubulin assembled into relatively shorter microtubules in the presence of saturating MAP-2. When assembly was induced with substoichiometric concentrations of taxol, in place of MAPs, the rate and extent of assembly were about twice as great with tyrosinolated tubulin.

Animals↗
PubMed1982

"Makings of a dacoit".

A study of the dacoits of the Chambal River valley was undertaken to determine what special circumstances exist to make them to take to dacoity, or whether these outlaws had a psychopathic disposition. The study sample consisted of 50 dacoits, compared with 50 aggressive criminals and 50 normals (non-criminals) from the same region. Among the most important factors contributing to their choosing this particular criminal career were: insecure childhood, enemity, psychopathic or wayward tendencies, belonging to a family of outlaws, rejection by society, extremely discordant family conditions, and the influence of operating dacoits.

Antisocial Personality Disorder↗
PubMed1982

Structure and function of the small bowel in lepromatous leprosy.

The structural and functional status of the small bowel was examined in ten patients with lepromatous leprosy. The absorptive functions were essentially normal in all patients except for minor abnormalities; one patient had mild steatorrhea and two others had derangement of D-xylose absorption. Barium examination did not reveal any abnormality in any patient. Histological study of the small intestinal mucosa showed mild, partial villous atrophy in two patients and normal appearances in the remaining eight. The above abnormalities were mild and were not considered to be of any clinical significance. It is therefore concluded that the small bowel is not commonly involved in lepromatous leprosy.

Adult↗
PubMed1981

Taxol-induced polymerization of purified tubulin. Mechanism of action.

Incubation of tubulin with taxol resulted in the assembly of tubulin in the absence of microtubule associated proteins. Optimum assembly occurred at approximately equal concentrations of tubulin and taxol. Both podophyllotoxin and colchicine inhibited the taxol-induced tubulin polymerization. Microtubules formed with taxol were also resistant to podophyllotoxin-induced depolymerization. The rate of tubulin subunit exchange into taxol-induced microtubules at steady state was 5-fold lower than into microtubule-associated protein (MAP2)-stimulated microtubules. There was a marked difference in the kinetics of tubulin polymerized in the presence of both taxol and MAP2 as compared to that obtained with either of them alone. In binding experiments, no competition was observed between taxol and MAP2 or the anti-tubulin drugs, e.g. colchicine, podophyllotoxin, and vinblastine.

Alkaloids↗
PubMed1981

Preferential action of a brain detyrosinolating carboxypeptidase on polymerized tubulin.

A carboxypeptidase purified from brain catalyzes the release of COOH-terminal tyrosine without further digesting tubulin. It is distinct from previously described carboxypeptidases, and appears to have specificity for tubulin as it is not inhibited by peptides and proteins with COOH-terminal tyrosine, and because, unlike carboxypeptidase A (which by removing tyrosine from aldolase causes its inactivation), this enzyme does not decrease aldolase activity. The enzyme detyrosinolates both self-assembly-competent (cycle-purified) and -incompetent (phosphocellulose-purified) tubulin. However, under assembly conditions the rate was 2-3-fold higher for competent tubulin. Preincubation of assembly-competent tubulin with podophyllotoxin or colchicine resulted in a parallel concentration-dependent inhibition of tubulin polymerization and detyrosinolation. Similarly, when incompetent tubulin was induced to polymerize by preincubation with purified microtubule-associated protein 2 (an assembly-promoting protein) or taxol, the initial rate of its detyrosinolation increased 3-5-fold, and this increase was blocked if podophyllotoxin was also added along with microtubule-associated protein 2 or taxol during the preincubation. Oligomers induced by adding vinblastine to incompetent tubulin were also detyrosinolated more rapidly, and the stimulation was abolished by maytansine, which has been shown to disperse the vinblastine-induced oligomers. When polymerized and subunit fractions were separated after a steady state mixture had been partially digested with the carboxypeptidase, the former was found to have lost 2-3 times more COOH-terminal tyrosine. Although both polymer and monomer can be detyrosinolated by the enzyme, polymeric and oligomeric forms are the preferred substrates. Carboxypeptidase appeared to release tyrosine at the same rate from populations of short and long microtubules.

Animals↗
PubMed1981

Interaction of tubulin with phospholipid vesicles. I. Association with vesicles at the phase transition.

Purified soluble tubulin will interact with highly sonicated small unilamellar vesicles of dipalmitoyl phosphatidylcholine. This results in the leakage of a fluorescent dye, carboxyfluorescein, from the internal aqueous space of the vesicles at the lipid phase transition. The amount of dye leaked from the vesicles is determined by the tubulin to vesicle ratio and partial dye leakage reflects the uniform leakage of carboxyfluorescein from all of the vesicles. Once tubulin interacts with dipalmitoyl phosphatidylcholine vesicles at the phase transition, it is unavailable to interact with additional vesicles. This interaction represents the formation of stable tubulin-vesicle recombinants as shown by density gradient centrifugation. Such recombinants are only formed by interacting the protein with the vesicles at the lipid phase transition temperature. The interaction is insensitive to ionic strength (0.001 to 4 M NaCl) and the recombinants remain stable for days.

Animals↗
PubMed1981

Interaction of tubulin with phospholipid vesicles. II. Physical changes of the protein.

We have shown that soluble tubulin will bind to small unilamellar vesicles of dipalmitoyl phosphatidylcholine (Klausner, R. D., Kumar, N., Weinstein, J. N., Blumenthal, R., and Flavin, M. (1981) J. Biol. Chem. 256, 5879-5885). This association uniquely occurs at the lipid phase transition. The tubulin, when bound to the vesicles, displays an altered tryptophan fluorescence characterized by a 5-nm blue shift in the emission maximum and a 22% decrease in fluorescence intensity, when compared to soluble tubulin. Tryptophans in vesicle-bound tubulin are less accessible to the aqueous collisional quenchers, acrylamide and iodide, than in soluble tubulin. Circular dichroism studies reveal an increase in alpha-helical content of tubulin as a result of vesicle interaction. Proteolytic digestion by trypsin of vesicle bound tubulin is slower than of soluble tubulin. The beta subunit of tubulin is preferentially protected from trypsin by vesicle interaction. Furthermore, the pattern of tryptic cleavage products is altered by this interaction.

Acrylamides↗