The behavior and facial expressions performed by cats have been reported to be visibly affected by the perceived taste quality of a food item. The goal of the present study was to assess how cats react to pleasant and unpleasant tastes. The facial and behavioral reactions of 13 cats to different concentrations of L-Proline and quinine monohydrochloride as well as mixtures with different concentrations of the two substances were assessed using a two-bottle preference test. The cats were videotaped during the tests and the frequency and duration of 50 different behaviors was analyzed in Noldus the Observer XT. The cats responded to tastes regarded as pleasant by having their eyes less than 50 % open for significantly longer periods of time compared to a water control. Tongue protrusions were also observed significantly more frequently when the cats sampled from a solution with a preferred taste compared to a water control. When encountering solutions of quinine monohydrochloride or mixtures containing quinine monohydrochloride the cats were observed to perform tongue protrusion gapes much more frequently compared to a water or L-Proline control. Even though the cats did not significantly differ in the number of times they licked at spouts containing the 50 mM L-Proline and 500 mM quinine monohydrochloride mixture compared to a 50 mM L-Proline, no masking effect could be confirmed as there was no increase in the acceptance of the mixture was observed. The present study suggests that the knowledge about behavioral responses to pleasant or unpleasant taste can be utilized in future studies on how cats perceive different tastes.

When proteins and DNA interact, arginine and lysine are the two amino acids most often in close contact with the DNA. In order to understand the radiation damage to DNA in vivo, which is always associated with protein, it is important to learn the radiation chemistry of arginine and lysine independently, and when complexed to DNA. This work studied X-irradiated single crystals of L-lysine monohydrochloride dihydrate (L-lysine·HCl·2H2O) and L-arginine monohydrochloride monohydrate (L-arginine·HCl·H2O) with EPR, ENDOR, EIE techniques and DFT calculations. In both crystal types irradiated at 66K, the carboxyl anion radical and the decarboxylation radical were detected. DFT calculations supported these assignments. Specifically, the calculations performed on the cluster models for the carboxyl anion radicals reproduced the proton transfers to the carboxyl group from the neighboring molecules through the hydrogen bonds. Moreover, computations supported the identification of one radical type as the guanidyl radical anion with an electron trapped by the guanidyl group. In addition, the radical formed by dehydrogenation of C5 was identified in the L-arginine·HCl·H2O crystals irradiated at 66K. For both crystal types, the deamination radicals and the dehydrogenation radicals were identified following irradiation at 298K. Different conformations of main-chain deamination radicals were detected at 66K and at 298K. In L-lysine·HCl·2H2O, these conformations are the result of the different rotation angles of the side chain. In L-arginine·HCl·H2O, one conformation at 66K has no O-H dipolar protons while the others have two O-H dipolar protons. In L-lysine·HCl·2H2O, two radicals with very similar sets of hyperfine couplings were identified as the result of dehydrogenation from C3 and C5. Two other radicals in low concentration detected only at 66K, were tentatively assigned as the radical dehydrogenated from C3 and the side-chain deamination radical. In L-argnine·HCl·H2O, the radicals from dehydrogenation at C5 and C2 also were identified. DFT calculations supported these assignments and reproduced conformations of these radicals.Finally, based on the radicals detected in the crystal irradated at 66K and at 298K, the annealing experiments from the irradiation at 66K, and the previous studies on the irradiated amino acids, the mechanisms of the irradiation damage on lysinie and arginine were proposed.