Aaron E. Wasserman

Initial Reaction Intermediates in the Oxidation of Ascorbic Acid by Nitrous Acid

Nitrite and ascorbate react to form nitric oxide at pH 5.5. In the initial stages of the reaction, seven intermediates can be identified spectrally and chromatographically; these include two colorless nitroso derivatives which contain 30-60% of the initial nitrite, two nitroso reductant derivatives absorbing at 345 and 412 nm, diketogulonic acid and two further decomposition products. None of the intermediates was paramagnetic; except for diketogulonic acid, all decomposed rapidly during or after isolation. Based on the order of appearance of the ultraviolet and visible absorption bands in the reaction mixtures, the observed characteristics of the intermediates, and the lack of organic radicals, a sequence is proposed for the initial steps in the oxidation of ascorbic acid by nitrous acid.

Heme-Protein-Ligand Interactions

Recent studies have suggested the use of nitrogenous heterocyclic compounds as color forming reagents in cured meats (Tarladgis, 1967; Howard et al., 1973). During screening in frankfurters of a variety of such compounds, including a series of substituted pyridines, we observed the production of a variety of colors. The principal colors were: purple, produced by strong electron acceptors in the 4 position on the pyridine nucleus; orange, produced by methylpyridine derivatives; and red or pink, produced by all other substituents in the 3 or 4 position. These results led us to a more detailed study of the spectra of these pigments, using bovine myoglobin in pH 5.5 buffer which is approximately the pH of meat.

Endogenous respiration of Serratia marcescens and oxidation of added carbohydrates.

Summary Endogenous oxygen consumption of Serratia marcescens, grown on a medium containing glucose at pH 4 and 7 or gluconate at pH 6, continues unchanged during oxidation of glucose and several other substrates. Correcting total oxygen consumption in the presence of a substrate for the endogenous oxygen consumption, affords an accurate representation of the course of oxidation of the substrates. S. marcescens grown in gluconate-containing medium at pH 4 has a higher endogenous oxygen consumption than cells grown on the other media. At one stage of the endogenous metabolism a sharp increase in rate of oxygen consumption occurs. Such sharp increase in oxygen consumption does not occur during oxidation of glucose and several other substrates. Hence correction of total oxygen consumption in the presence of the substrates for endogenous respiration of the cells may lead to an erroneous interpretation of the data.