Are cytoplasmic microtubules heteropolymers?

Colchicine-binding protein, considered to be microtubule protein, was purified from chick embryo brain by column chromatography in one step on DEAE-Sephadex. The active colchicine-binding unit is a dimer, MW 115,000 +/- 5000, which is composed of two nonidentical monomeric units. The two subunits are separable by urea-acrylamide gel electrophoresis after they have been reduced and acetylated. Sodium dodecyl sulfate-acrylamide gel electrophoresis indicates that the subunits both have molecular weights of 55,000 +/- 2000. The amino-acid compositions of the two subunits showed statistically significant differences in six amino-acid residues. These results indicate that colchicine-sensitive cytoplasmic microtubules are heteropolymers.

Precipitation of proteins by vinblastine and calcium ions

We have found that vinblastine sulfate can precipitate a number of proteins in addition to microtubule protein. Those proteins which precipitate with vinblastine sulfate, all of which were derived from structure, also precipitate with Ca(2+) ions. Our results suggest that vinblastine sulfate, presumably acting as a cation, precipitates proteins by combining with sites which can also combine with Ca(2+) ions.

Compensation for auditory re-arrangement following exposure to auditory-tactile discordance

15 Os presented with discordant auditory and tactile information about the location of the same object, compensated rapidly for an auditory re-arrangement when asked to point at an unseen auditory target. Unlike most perceptual compensation studies, movement by O was not permitted. It is suggested that discordance between or among different kinds of spatial information may be the condition that leads to compensation for re-arrangement.

The interaction of alpha-chymotrypsin with isosteric substrates of different charge type

1. The synthesis of three substrates of alpha-chymotrypsin of closely similar steric requirements but different charge type is reported. 2. The interaction of these compounds [SS-dimethyl-(l-3-carboxymethyl-3-acetamido)propyl sulphonium iodide, l-2-acetamido-5-methylhexanoic acid methyl ester and N-acetyl-l-glutamic acid alpha-methyl ester] with alpha-chymotrypsin has been studied. 3. For the charged substrates, values of k(0) are two orders of magnitude smaller than, and values of K(m) two orders of magnitude larger than, the corresponding values for the uncharged isostere. 4. The results are interpreted in terms of the known specificity of the enzyme, and the relationship between binding and kinetic specificities is discussed.

Compensation for auditory re-arrangement in hand-ear coordination

10 Ss pointed at concealed auditory targets while listening through a pseudophone which produced 20° functional rotation of the interaural axis. After short exposures listening to a sound source held in one hand while moving that hand about, large and significant corrective shifts in pointing were measured.

Water-soluble inhibitor(s) of tumor respiration formed from ultraviolet-induced oxidation of linoleic and linolenic acids

Inhibition of Ehrlich ascites carcinoma respiration by aqueous extracts of oxidized linoleic or linolenic acid (aqueous emulsions UV-irradiated, 90 min) was associated entirely with relatively involatile compounds which were both thiobarbituric acid (TBA)-reactive and peroxidase-reactive. Inhibitory compounds were heat stable and migrated in thin-layer chromatography with aldehydes, "hydroperoxides," and TBA-reactive compounds. Peroxidase-catalyzed reduction of the "hydroperoxide" diminished the inhibition. At 4.7 x 10(-5) M "hydroperoxide" concentration, the residues from both linoleic and linolenic acid inhibited tumor oxygen consumption to a similar degree. However, at this concentration of "hydroperoxide" only the dried extract from linolenic acid was able to produce inhibition (100%) of aerobic glucose utilization by tumor cells. No glycolytic inhibition by the dried residue of oxidized linoleic acid was observed. At least 12 compounds (approximate chain length, 7C-13C) containing alpha,Beta-unsaturated carbonyl groups were isolated by gas-liquid chromatography (GLC) of dried extracts of oxidized linolenic acid. No single fraction inhibited tumor respiration, but the recombined mixture of all compounds caused complete respiratory inhibition of ascites tumor cells. Less material was required to inhibit oxygen consumption before than after GLC presumably because the more highly inhibitory components of the extract (along with "hydroperoxides" and TBA-reactive compounds) were lost during GLC. Extracts from oxidized linolenic acid were found to produce in all tumor cells cytoplasmic evaginations which were readily detected by phase microscopy.

Water soluble products of UV-irradiated autoxidized linoleic and linolenic acids

The water-soluble products of the UV-initiated autoxidation of linoleic and linolenic acids emulsified in water were separated into volatile and relatively involatile components, each of which reacted with both thiobarbituric acid (TBA) and peroxidase. The volatile TBA-reactive compound is probably malonaldehyde and the volatile peroxidase-reactive compound is hydrogen peroxide. Additional compounds which absorb UV light were present in the volatile fraction. After thin-layer chromatography of the involatile fraction, reactivity toward TBA and peroxidase was found in the same spot. Approximate molar yields of hydrogen peroxide, malonaldehyde, "hydroperoxides", and other TBA-reactive compounds were estimated. The ratio of "hydroperoxide" to TBA reactivity was lower for linoleic than for linolenic acid. The mass of relatively involatile compounds was about 20 times greater than that predicted from either peroxidase or TBA assays of water extracts of oxidized linolenic acid. The properties of the water extract were similar to those shown by others for the products of prolonged autoxidation (without UV-irradiation) of emulsified methyl linoleate.