The photodecomposition of tryptophan peptides

Aqueous solutions of the four trytophan peptides, Ala-Trp-Val, Val-Trp-Ala, Ala-Ala-Trp-Val and Ala-Gly-Trp-Leu, have been irradiated with light of wavelengths >295 n. The major changes were destruction of the tryptophan residue, liberation of ammonia and the formation of photoproducts of increased molecular weight. Up to 40% of Ala-Ala-Trp-Val and Ala-Gly-Trp-Leu were converted to products with molecular weights ranging from two to four times those of the original tetrapeptides. Most of the yellow material formed during irradiation in air was present in the high molecular weight fractions. Irradiation of Ala-Gly-[¹⁴C]Trp-Leu gave the following identifiable photoproducts: Ala-Gly-Asp-Leu, Ala-Gly-(N′-formyl)Kyn-Leu, Ala-Gly-Oia-Leu, and ammonia, where Kyn means kynurenine and Oia, β-(3-oxidolyl)alanine.     

A simple quantitative method for the determination of 3-fluorotyrosine substitution in proteins

A rapid quantitative method is described for determining 3-fluorotyrosine incorporation into proteins. Derivatives of tyrosine and 3-fluorotyrosine with o-phthalaldehyde are well separated from one another by a reverse-phase high-performance liquid chromatography system used for routine analyses of o-phthalaldehyde-amino acid derivatives. Since both amino acids are well resolved from all other derivatized amino acids, the method is useful for amino acid analyses of proteins. Determination of the fluorotyrosine content of proteins by this method involves a single separation step, is reproducible, and requires no corrections for stability or yield. Further, the o-phthalaldehyde derivatives of 5-fluorotryptophan, 2-fluorophenylalanine, 3-fluorophenylalanine, and 4-fluorophenylalanine can also be resolved. The method may be generally applicable to fluorinated aromatic amino acid-labeled proteins that are studied structurally and dynamically by nuclear magnetic resonance.     

The chemical stimulus essential for growth by increase in cell number

Summary The development of this study has been a succession of steps each of which rests on the preceding. It falls naturally into three distinct stages. The first is that ofIdentification Here it was found that the lead precipitate present in the meristematic region of root tips grown in Pb-containing culture solutions is a combination of lead with sulfhydryl. In such tips mitosis but not growth by increase in cell size is inhibited. Also it was found that sulfhydryl is concentrated in the meristematic region of normal roots. Therefore the hypothesis was developed that growth by increase in cell number is specifically factored by -SH. The next stage was theTesting of Extracts Here it was found that acid extracts of the meristem of root tips accelerated root length growth when controlled by acid extracts of the next distal portion, while alkaline extracts similarly controlled showed no such activity. This proved that the root region of highest sulfhydryl concentration and mitotic activity contains a naturally occurring acid-stable, alkali-labile substance stimulative of root growth in length. These findings are thus physiologically and chemically consistent with the hypothesis. The next stage was theTesting of Synthetic Compounds Here the action of a variety of sulfhydryl compounds on mitosis in root tips and reproduction rate in Paramecium was studied, using the same compounds minus the sulfur moiety as controls. It was found that the -SH group stimulates cell division in both plants and animals. Cell size growth is not stimulated. Thus, through identification and testing of the identified group in natural and synthetic compounds, the conclusion is arrived at that Sulfhydryl is the essential stimulus to growth by increase in cell number.Credit is due to MissElizabeth Justice and MissJane Anderson whose conscientious and painstaking efforts made this study possible.     

Polyplax serrata: Effects of limb disability on lousiness in mice: VI. Lack of tolerance after neonatal exposure

Mice restrained from grooming become heavily infested with lice. Ordinarily the hosts develop resistance to the infestation which results in limitation or extinction of louse populations. However, individual mice, the number depending on breed, die of anemia or, in some cases, become debilitated but survive with continuous heavy louse burdens. A similar condition of tolerance is occasionally seen in domestic animals. Experiments were conducted to determine whether heavy exposure to lice in the neonatal period could induce tolerance to the parasite. When adequate provision was made to prevent mortality from louse infestation, survival and acquisition of resistance developed at the same rate and to the same degree in neonatally exposed and in naïve mice.     

Effects of ethanol in vitro on rat intestinal brush-border membranes

Ethanol, at concentrations found in the intestinal lumen after moderate drinking, has been shown to inhibit carrier-mediated intestinal transport processes. This inhibition could occur by direct interaction with membrane transporters, dissipation of the energy producing Na⁺ electrochemical gradient and/or nonspecific alteration of membrane integrity. The latter alteration may be reflected by changes in membrane fluidity, chemical composition or vesicular size. These possibilities were examined with studies in purified brush border membrane vesicles of rat intestine. Ethanol inhibited concentrative Na⁺-dependent d-glucose uptake in a dose-dependent manner. In contrast, ethanol did not inhibit concentrative d-glucose uptake under conditions of d-glucose trans-stimulation in the absence of a Na⁺ electrochemical gradient. Ethanol also inhibited initial, concentrative Na⁺-dependent taurocholic acid uptake, as well as equilibrium uptake. That ethanol exerted a dual effect on transport by increasing membrane conductance for Na⁺ while decreasing intravesicular space was supported by direct studies of Na⁺ uptake. Morphometric analysis confirmed that ethanol-treated membranes had a decreased intravesicular size when compared to untreated membranes. Finally, membrane fluidity measured by EPR showed that ethanol had a significant fluidizing effect without producing qualitative changes in membrane proteins, as determined by SDS gel electrophoresis. These results suggest that ethanol inhibits carrier-mediated transport by dissipation of the Na⁺ electrochemical gradient and alteration of membrane integrity rather than by direct interaction with membrane transporters.