Ultraviolet and visible spectroscopy was applied to characterize and to measure the concentration of b-carotene dissolved in a dioxane and water mixture. The reaction of b-carotene in the presence of nitrite anion and acid medium was studied at different temperatures. The reaction systems were homogeneous and were kept anaerobic. Pseudo-first-order rate constants in respect of bcarotene were measured in the range from 293 to 313 K and pH 5.8 ) 0.2. The energy of activation was calculated to be E a " 67.2 ) 3.4 kJ/mol. We interpolate a value that may have biological interest, k b-carotene (310 K) " (9.70)0.78)$10 #3 s #1 , in the presence of 9.3$10 #3 M nitrite anion. Electron paramagnetic resonance spectroscopy was applied to characterize and quantify a persistent intermediate radical generated in the reaction system described. The recorded spectra showed triplet-type signals with a peak-to-peak value of 12.7 G. Nearly the same triplet radical-type intermediates were detected when studying the following reaction systems in pure dioxane: nitrogen dioxide (NO 2 )/b-carotene, nitric oxide (NO)/b-carotene and NO/NO 2 /b-carotene. Therefore, we proposed that the nitrogen oxides have also been intermediates in the reaction system of b-carotene, nitrite anion and acid medium, in the dioxane and water mixture. A mechanism was proposed and checked by employing the chemical kinetics simulation. The explanations developed would lead to a better understanding of the behavior of carotenoids in the presence of nitrite anion and nitrogen oxides.

Free radical scavenging properties of hepatopancreas extracts of Pleoticus muelleri were evaluated by electron paramagnetic spin resonance spectrometry methods (EPR) against the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The present study was carried out to characterize different physiological stages of the shrimp under environmental and nutritional stress, evaluating the effect on growth, survival, and functional morphology of the hepatopancreas. Feeding trials were carried out on juveniles (1 g initial weight) held in aquaria. Each diet, with different concentrations of vitamins A and E, was tested in triplicate groups during 25 days. The control groups were fed with fresh squid mantle and with a vitamin-free diet. For all of the diets, the extracts exhibited strong DPPH radical scavenging activity, suggesting that the tissue is a powerful natural antioxidant. Individuals fed with different concentrations of vitamin E showed the strongest effect on the DPPH radicals, reducing the DPPH radicals to 50%, after an incubation period of 3 min. In contrast, the extracts of control animals, fed with squid mantle, had the weakest antioxidant activity (4%). These data indicated that the presence of vitamin E in the diet can provide immediate protection against free radicals.

The dissociation equilibrium of N204-NO 2 has been measured in hexane, carbon tetrachloride and chloroform at different temperatures. The equilibrium constants at 298.15 K (25~ K,, (molality basis), are 3.5.10 -~ in hexane, 5.9-10 -6 in carbon tetrachloride and 5.3 9 l0 -6 in chloroform. The EPR technique has been used to quantify the NO_, radical. These data are compared with gas-phase and solution data of previous reports. The applicability of Hildebrand and Scatchard theory of solutions is also discussed and some thermodynamic properties are deduced, such as Henry's N204 and NO 2 constants in different solvents.

4) Walters, V. A.; Haddad, C. M.; Thiel, Y.; Colson, S. D.; Wiberg, K. B.; Johnson, P. M.; Foresman, B. J. J. Am. Chem. Soc. 1991, 113, 4782. (5) Bent, G. D.; R w i , A. R.Rates of the prompt formation of (HSO,),NO'(F) in the reaction of nitrous acid with bisulfite were measured by stopped-flow electron spin resonance spectrometry at pH = 3.0-5.8, 298 K. Initial rates have a positive dependence on (HONO] and [HSOy] but decrease markedly with pH. The induction periods observed in air-saturated solutions are s u p p d by addition of 2 mM hydroxylaminedisulfonate, (S03-)2NOH (FH), revealing a free-radical precursor to F. The spin trap 5.5-dimethyl-1-pyrroline N-oxide (DMPO) also inhibits the formation of F but withour producing newparamagneric species, ruling out monoradical intermediates. We show that these observations are consistent with the previously proposed participation of a nitrene, HON:, in this system. Present evidence suggests that the title reaction is a potential source of free radicals in natural environments.

A potato particulate preparation, which is constituted mainly by proplastids, was capable of glucose transfer from micromolar concentrations of uridine diphosphate ['4C]glucose into an endogenous protein molecule to form a 14C-labelled glucoprotein. This glucoprotein had short radioactive glucan chains and could act as acceptor for the synthesis of larger radioactive glucan chains from labelled uridine diphosphate glucose, either at millimolar concentrations or in the presence of glucose 1 -phosphate or adenosine diphosphate glucose at micromolar concentrations. This last step required MnZ+ or M 2 + ions.The enzyme responsible for the formation of the glucoproteic acceptor was named uridine diphosphate glucose-protein transglucosylase I and its properties were studied.The uridine diphosphate glucose-protein transglucosylase activity, that was detected at micromolar uridine diphosphate glucose concentrations in the presence of glucose l-phosphate, could be distinguished from uridine diphosphate glucose -protein transglucosylase I by the following criteria: The glucose l-phosphate dependent activity required MnZ + or MgZ+ ions, was sensitive to temperature and formed radioactive glucan chains totally hydrolyzed by /&amylase. Conversely, uridine diphosphate glucose-protein transglucosylase I was active in the absence of Mn" or M g + ions, was resistent to temperature and formed radioactive glucan chains scarcely attacked by fl-amylase.Sequential analysis of the glucose incorporation from uridine diphosphate [3H]glucose and uridine diphosphate ['4C]glucose into the glucoprotein and sodium dodecylsulphate -acrylamide gel electrophoresis of the labelled glucoproteins formed in the presence and in the absence of glucose l-phosphate were carried out.On the basis of the data obtained a simple scheme of reactions is proposed to explain the involvement of the uridine diphosphate glucose -protein transglucosylase I and glucose 1-phosphate dependent activities in the synthesis of a-1,4 glucan chains of the starch type.Starch synthetase plays a main role in the formation of the complex structure of starch granules in plant cells. This enzyme, which is capable of synthesizing a-1,4 glucosidic chains, can be found in a particulate form, bound to the starch granule [1,2] and in a soluble state [3 -71. The specificity of the two forms of starch synthetase appears to be different. While reserve starch granules of potato and cereal grains can use ADP-glucose, UDP-glucose and other sugar nucleotides as glucosyl donors, the soluble enzymes transfer glucose specifically from ADP-glucose [2]. The latter specific requirement is also reported for certain starch granules [S, 91. These differences suggest that the particulate and soluble starch synthetases are different enzymes and the loss of the capability to use UDP-glucose, which is observed in starch granules after grinding and urea treatment [lo] supports this hypothesis.With regard to the initiation of starch biosynthesis the question remains as to the origin of primer in vivo. Star...