Characterization of a β-Galactosidase Formed Between a Complementary Protein and a Peptide Synthesized De Novo

In a cell-free system, phi80dlac can be transcribed, and the resulting ribonucleic acid can be translated to yield a product which interacts with an enzymatically inactive z protein to produce active enzyme. The inactive z protein is produced by Escherichia coli strain 21, which contains a deletion in the first part of the gene for beta-galactosidase and appears to exist as a dimer. The enzyme formed in the cell-free system appears to be composed of one strain 21 z protein dimer and one newly synthesized polypeptide chain with a molecular weight of about 3 x 10(4). The estimated size of this complementing segment is in good agreement with Ullmann, Jacob, and Monod's estimate of the size of the alpha region of beta-galactosidase. Using alpha fragments produced by autoclaving or guanidine treatments, we found that the active portion of alpha seems to be smaller than the full alpha region. We also found, using alpha produced by the autoclaving technique, that active dimer undergoes conversion to tetramer as the amount of alpha is increased. Evidently, the binding of alpha favors this conversion, but it is unlikely that the conversion of dimer to tetramer per se results in increased enzyme activity.     

Glycoprotein and protein antifreezes in two Alaskan fishes.

Two macromolecular freezing point depressants have been isolated from the serums of two species of Alaskan fishes. A common property of the four antifreezes thus far isolated is a high alanine content which suggests that the mechanism of these antifreezes may be related to a repeating tripeptide unit.     

Effects of chorda tympani nerve anesthesia on taste responses in the NST

Human clinical and psychophysical observations suggest that the taste system is able to compensate for losses in peripheral nerve input, since patients do not commonly report decrements in whole mouth taste following chorda tympani nerve damage or anesthesia. Indeed, neurophysiological data from the rat nucleus of the solitary tract (NST) suggests that a release of inhibition (disinhibition) may occur centrally following chorda tympani nerve anesthesia. Our purpose was to study this possibility further. We recorded from 59 multi- and single- unit taste-responsive sites in the rat NST before, during and after recovery from chorda tympani nerve anesthesia. During anesthesia, average anterior tongue responses were eliminated but no compensatory increases in palatal or posterior tongue responses were observed. However, six individual sites displayed increased taste responsiveness during anesthesia. The average increase was 32.9%. Therefore, disinhibition of taste responses was observed, but infrequently and to a small degree in the NST At a subset of sites, chorda tympani-mediated responses decreased while greater superficial petrosal-mediated responses remained the same during anesthesia. Since this effect was accompanied by a decrease in spontaneous activity, we propose that taste compensation may result in part by a change in signal-to-noise ratio at a subset of sites.