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Biomedical subjects

C M Lin

Publications and source records attributed to C M Lin.

At least 127 records · Page 7Linked to original sources
PubMed1982

Effects of organic acids on tubulin polymerization and associated guanosine 5'-triphosphate hydrolysis.

We have examined the effects of a number of organic anions, which stabilize tubulin, on tubulin polymerization, associated GTP hydrolysis, and polymer morphology. While microtubule-associated proteins, as well as glycerol, induced formation of typical microtubules in a reaction coupled to GTP hydrolysis at an initial 1:1 stoichiometry, the organic anions had varying effects. Only 2-(N-morpholino)ethanesulfonate induced formation of structures with the morphology of microtubules. With glutamate, fructose 1,6-bisphosphate, piperazine-N-N'-bis(2-ethanesulfonate), glutarate, and glucose 1-phosphate, the predominant structures formed were sheets of parallel protofilaments rather than microtubules. Creatine phosphate induced the formation of clusters of rings. GTP hydrolysis was closely coupled to polymerization only with glutamate. With creatine phosphate, there was minimal GTP hydrolysis. With all other organic anions, GTP hydrolysis substantially exceeded polymerization at all time points, with the onset of hydrolysis significantly preceding the onset of turbidity development. Nevertheless, the rate of GTP hydrolysis was a sigmoidal function of tubulin concentration under all conditions examined, suggesting that tubulin-tubulin interactions are required for hydrolysis. All anion-induced reactions were temperature dependent and cold reversible, but only the creatine phosphate induced reaction was not inhibited by GDP, CA2+, or colchicine and did not require GTP.

Animals↗
PubMed1982

Tubulin-dependent biochemical assay for the antineoplastic agent taxol and application to measurement of the drug in serum.

A biochemical assay for taxol with sensitivity to 0.1 microM has been developed. Taxol-dependent formation of tubulin polymers occurs at 37 degrees C in 1.0 M glutamate in the absence of GTP. These polymers are cold-stable and hydrolyze GTP at 0 degrees C, whereas tubulin alone will not hydrolyze the nucleotide in the cold. This assay has been used to follow rabbit serum levels of taxol injected iv. Although the drug appears to be almost totally protein-bound, it is nevertheless rapidly cleared from serum. The apparent alpha-phase and beta-phase half-lives after iv bolus administration in one rabbit are 2.7 and 42 mins, respectively.

Alkaloids↗
PubMed1981

Effects of inhibitors of tubulin polymerization on GTP hydrolysis.

The effects of a number of antimitotic drugs on the GTPase activity of tubulin were examined. The previously reported stimulation with colchicine and inhibition with podophyllotoxin and vinblastine wee confirmed. Maytansine, which competes with vinblastine in binding to tubulin, was comparable to the latter in inhibiting GTP hydrolysis. Nocodazole, which competes with colchicine in binding to tubulin, was significantly superior to colchicine in enhancing GTP hydrolysis. This superiority arose from the more rapid bindng of nocodazole to tubulin, as the two drugs had comparable activity when drug and tubulin were preincubated prior to the addition of GTP. Both colchicine and podophyllotoxin contain a trimethoxybenzene ring, while the closest structural analogy of nocodazole to colchicine includes the trimethoxybenzene ring. To explore this apparent paradox, we examined a number of simpler colchicine analogs for their effects on tubulin-dependent GTP hydrolysis. While tropolone was without effect, 3,4,5-trimethoxybenzaldehyde and 2,3,4-trimethoxybenzaldehyde stimulated the reaction. We therefore conclude that the trimethoxybenzene ring of colchicine is primarily responsible for the drug's stimulation of the GTPase activity of tubulin and that the inhibitory effect of podophyllotoxin must derive from the latter's tetrahydronaphthol moiety.

Animals↗
PubMed1981

Stabilization of the colchicine-binding activity of tubulin by organic acids.

A number of carboxylic acids and organic phosphates were found to be highly effective in stabilizing the colchicine-binding activity of calf brain tubulin. The most active were glutamate, glutarate, delta-aminovalerate, glucose 1-phosphate, glucose 6-phosphate, fructose 1,6-(bis)phosphate, creatine phosphate and 6-phosphogluconate Maximum effects occurred at high concentrations. Combinations of agents were also examined, and the most effective mixture for stabilizing tubulin found thus far was the combination of 1.0 M glutamate, 100 mM glucose 1-phosphate, 1 mM GTP and 0.5 mg/ml of albumin. No loss of activity occurred over 48 h at 37 degrees C with tubulin was present at a concentration of 100 microgram/ml.

Animals↗
PubMed1981

Interaction of tubulin with ribose-modified analogs of GTP and GDP: evidence for two mutually exclusive exchangeable nucleotide binding sites.

Interactions of tubulin with a number of guanine nucleotides modified at the 2' and 3' ribose hydroxyls were examined. Deoxy analogs of GTP were equal or superior to GTP in supporting tubulin polymerization, but analogs bearing either methyl or phosphate groups on the hydroxyls had significantly reduced ability to support polymerization. These substituted GTP analogs were hydrolyzed at the 5'-gamma-phosphate position, although less rapidly than GTP, at rates exceeding those of polymerization. GTP hydrolysis, however, was closely coupled to polymerization. Moreover, the partially active GTP analogs were not effective inhibitors of GTP-dependent polymerization. These data indicate that the substituted GTP analogs have reduced affinity for tubulin at the exchangeable site because of steric factors. No deoxy or substituted GDP analog was as effective as GDP itself in inhibiting GTP-supported tubulin polymerization. Furthermore, there was no apparent relationship between the ability of nucleoside 5'-triphosphates to support polymerization and that of nucleoside 5'-diphosphates to inhibit the reaction. These findings suggest that GTP and GDP may actually bind to different, mutually exclusive sites rather than to a single exchangeable site.

Animals↗
PubMed1981

Binding of maytansine to tubulin: competition with other mitotic inhibitors.

The effect of maytansine on the binding of [3H]vinblastine and [3H]colchicine to tubulin was examined by Sephadex gel filtration column chromatography. When varying concentrations of maytansine were employed, competition between vinblastine and maytansine was observed at a vinblastine to maytansine ratio of 1:10 and 1:100, while a colchicine to maytansine ratio of 1:100 did not affect the binding of colchicine to tubulin. These results confirm earlier findings with a DEAE-cellulose disc paper assay and a tubulin polymerization assay that maytansine shares a common binding site with vinblastine and support the view that tubulin has at least two drug binding sites.

Animals↗
PubMed1979

Antigenic analyses of two axenized strains of Entamoeba histolytica by two-dimensional immunoelectrophoresis.

Antigens in extracts of two strains of Entamoeba histolytica (HT-31 and HK-9) were studied by two-dimensional immunoelectrophoresis (2D-IEP) and 32 and 20 different antigenic components were detected, respectively. Cross-reactions between heterologous systems showed a large number of shared antigens between the two strains. Extracts were fractionated by Sephadex G-200 chromatography. Of the fractions obtained, fraction II of both strains was found to have the most reactive antigenic components. Precipitin patterns of fraction II from HT-31 and HK-9 with sera from patients showed similar 2D-IEP profiles and suggested that in this fraction antigens common to both strains exist which elicit antibody in individuals with E. histolytica infections.

Animals↗
PubMed1978

Reliability of goniometric measurements.

This study determined the intratester and intertester variability and reliability of goniometric measurements taken by four physical therapists on upper and lower extremity motions of normal male subjects. The same subjects were measured once weekly for four weeks by testers with varied experience in goniometry. Data were analyzed by analyses of variance with repeated measures. Intratester variation for all measurements was less than intertester variation. Further, intertester variation was less for the three upper extremity motions than for those of the lower extremity. These findings indicate the necessity for using the same tester when effects of treatment are evaluated. When the same tester measures the same movement, increases in joint motion of at least three to four degrees determine improvement for either the upper or lower extremity. When more than one tester, however, measures the same movement, increases in joint motion should exceed five degrees for the upper extremity and six degrees for the lower extremity to determine improvement.

Adult↗
PubMed1976

Comparison of some methods for the detection of antigen-antibody reactions in amoebiasis.

The indirect hemagglutination test (IHA) and counterimmuno-electrophoresis (CIE) were used to test for antibodies to Entamoeba histolytica in human sera using antigens from axenic cultures of the HK9 strain. Correlation between the test was excellent with most sera from patients with amoebiasis demonstrating precipitin lines by CIE at IHA titers considered diagnostically positive, larger than or equal to 1:128. Precipitin reactions with positive sera were also compared by CIE, immunoelectrophoresis (IEP) and two-dimensional electrophoresis is (2D-IEP). The greatest number of antigen-antibody components were demonstrated by 2D-IEP. Further studies utilizing 2D-IEP should be of value in the antigenic analysis of E. histolytica.

Amebiasis↗