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Estuarine and coastal waters of a selected area of the Tyrrhenian Sea were analysed for dissolved organic carbon (DOC), absorption and fluorescence properties. Coastal DOC values ranged from 0.88 to 1.37 mgL-1 with an average of 1.1 mg L-1. Absorption coefficients measured at 280 nm (a280) and 355 nm (a355) were in the range 0.95-2.3 m-1 (average 1.52 m-1) and 0.14-0.57 m-1 (average 0.27 m-1), respectively. The slope of the log-linearized absorption spectra, S, ranged from 0.012 to 0.029 nm-1 with a mean value of 0.019 nm-1. Normalized fluorescence, excited at the same wavelengths of the absorption measurements, F n(280) and Fn(355), exhibited mean values of 0.07 and 0.77 N.FI.U., and the quantumyields, Phi280 and Phi355, had mean values of 0.0014 and 0.0065, respectively. The chromatographic behavior of a riverine and a coastal sample, compared with that of a solution of commercial humic acid, used as standard, shows a variation in the chromatographic signature to which corresponds a decrease in the apparent molecular weight (Mr). Also taking into account the solar radiation regime of the sample collection period, these data show the occurrence of a CDOM (chromophoric dissolved organic matter) fluorescence photobleaching just in the first few miles off the coast. [ABSTRACT FROM AUTHOR]

In this study, we present results on seasonal and spatial changes in CDOM absorption and fluorescence (fCDOM) in a deep mountain lake (Salto Lake, Italy). A novel approach was used to describe the shape of CDOM absorption between 250-700 nm (distribution of the spectral slope, S(lambda)) and a new fluorescence ratio is used to distinguish between humic and amino acid-like components. Solar ultraviolet irradiance, dissolved organic carbon (DOC), DOM fluorescence and absorption measurements were analysed and compared to other physicochemical parameters. We show that in the UV-exposed mixed layer: (i) fluorescence by autochthonous amino acid-like CDOM, (ii) values of S(lambda) across UV-C and UV-B wavebands increased during the summer months, whereas (i) average molar absorption coefficient and (ii) fluorescence by allochthonous humic CDOM decreased. In the unexposed deep layer of the water column (and in the entire water column in winter), humic-like CDOM presented high values of molar absorption coefficients and low values of S(lambda). UV attenuation coefficients correlated with both chlorophyll a concentrations and CDOM absorption. In agreement with changes in CDOM, minimal values in UV attenuation were found in summer. The S(lambda) curve was used as a signature of the mixture between photobleached and algal-derived CDOM with respect to the unexposed chromophoric dissolved compounds in this thermal stratified lake. Furthermore, S(lambda) curves were useful to distinguish between low and high molecular weight CDOM.

A procedure for the coupling at pH 7.2 of p-carboxy benzene diazonium chloride with rabbit muscle aldolase supported on phosphocellulose is described and some of the spectroscopic, structural and catalytic features of the material obtained are reported. The tetrameric azoenzyme is homogeneous in disc gel electrophoresis even in the presence of 8 M urea. Twelve molecules of the reactant are bound to the protein. Eight azocysteins are identified by both spectroscopic studies and amino acid analysis. The presence of one azohistidine is suggested by the spectroscopic data along with the presence of other, as yet unknown, chromophores. The azoaldolase shows unchanged catalytic properties using both D-fructose 1,6-bisphosphate and D-fructose 1-phosphate as substrates, as compared with the native enzyme. The pH profile of the enzyme activity is broadened towards the alkaline region but no changes occur in the physiological range of pH.

pH Conditions have been found which achieve selective reaction of diazotized p-amino benzoate with cysteine residues of rabbit muscle aldolase. The difference in reactivity of the two sulphydryl groups involved, (Cys--237 and Cys--287) permits one to form either four or eight diazothioethers on the tetrameric enzyme and obtain a homogeneous protein. In both cases the enzyme became slightly more active in the fructose-1, 6-bisphosphate cleavage, the KM value being retained. The results have been discussed with regard to chemically modifying an enzyme to change its physical, chemical and immunological properties, whilst leaving the catalytical activity unmodified.