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The enzyme system composed of human neutrophilic myeloperoxidase (H2O2-oxidoreductase, EC 1.11.1.7), H2O2 and Cl-, at pH 4.5 interacts with egg white lysozyme (EC 3.2.1.17) in several stages. In the first stage, occurring at lysozyme to H2O2 molar ratio of 1:1.4-1.8, the lysozyme loses its enzyme activity but does not yield any derivative distinguishable from the native protein on polyacrylamide gel electrophoresis (PAGE). The second stage of oxidation begins at lysozyme to H2O2 molar ratio above 1:5, producing a change in the lysozyme spectrum at 260-290 nm, and yielding protein derivatives with molecular masses equal to multiples of 14.3 kDa, i.e. the lysozyme molecular mass. This implies that an excessive oxidation of lysozyme by the myeloperoxidase-H2O2-Cl- system produces cross-linking of lysozyme molecules to di-, tri-, tetra-, and pentameric structures. At lysozyme to H2O2 molar ratio exceeding 1:12 a water insoluble white product, which consists of a set of lysozyme cross-linked derivatives, is obtained.

Ribonuclease (RNase) activity is detectable in only one third of specimens of human erythrocyte haemolysates. On the other hand, treatment of erythrocytic cytosoles with sulphosalicylic acid reveals an inhibitor-bound RNase activity which is present in all erythrocyte specimens studied. The level of the erythrocyte inhibitor-bound RNase activity is comparable to that in human lymphocytes. Isolated RNase from the cytosolic fraction of human erythrocytes is poly-C avid RNase with maximum activity at pH 6.5. The enzyme is resistant to treatment with strong acids and heating up to 95 degrees C. Molecular filtration of the erythrocyte RNase shows that it is composed of two fractions differing in molecular mass, 19 000 and 15 000. No difference in enzymic properties between these fractions was found. The general properties of erythrocyte cytosolic RNase are much like those of acid RNases of human granulocytes and lymphocytes. As the erythrocytes do not metabolize RNA no function for the inhibitor-bound RNase can be suggested. Assuming that the observed erythrocyte RNase is the residual enzyme, persisting in the cell since it was functioning in the nucleated erythrocyte precursors, one may surmise that levels of free and inhibitor-bound erythrocyte RNase activity may be related to the normality or abnormality of erythrocyte maturation.

Ribonuclease (Ribonucleate nucleotide 2'-transferase E.C. 2.7.7.17) activity in serum of patients with chronic granulocytic leukaemia measured at pH 4.5-6.0 amounts to more than three times of that in serum of healthy subjects. At pH 6.0-8.0 the elevation of ribonuclease activity in serum of patients with chronic granulocytic leukaemia is less pronounced and amounts to about two times of that in normal ones. Using chromatography on CM Sephadex C-50 column, serum ribonuclease of both normal and chronic granulocytic leukaemia patients was separated into five distinct fractions. In serum of healthy subjects ribonuclease fractions denoted I-V contribute to 10; 21; 29; 22, and 18 percent of the total ribonuclease activity. In the serum of patients with chronic granulocytic leukaemia a decrease in ribonuclease fraction III to merely 17 percent and an increase in contribution of fraction IV to 32 percent of total ribonuclease activity could be observed. The comparison of each individual concentration of fraction in normal and leukaemia patients serum reveals, that ribonuclease fraction IV will increase about 3 times. A less pronounced increase could also be found for fractions I, II and V. However, ribonuclease fraction IV may be supposed to carry more than 50 percent of the whole extra load of ribonuclease present in the serum of chronic granulocytic leukaemia patients.

Data from four central European dietary investigations carried out between 1982 and 1984 in the German Democratic Republic, Poland and the Federal Republic of Germany applying both a food frequency questionnaire (FFQ) and a quantitative recording instrument (24-h recall, 3-d record or 10- to 14-d record) were analysed to compare frequency of food consumption as reported by the FFQ with the corresponding information as derived from the quantitative instrument. The actual intake was found to be overestimated by the FFQ for categories of frequent consumption and underestimated for categories of rare consumption. Categories for which both instruments yielded similar estimates of frequency were found to vary between food items and to depend on the overall frequency of consumption of an item. This indicates that when using unvalidated FFQs and taking their FFQ-categories literally artificial differences of food consumption within the population(s) under study can be introduced. This implies also the tendency that the average food intake estimated through FFQs can yield unrealistically high values for items consumed frequently.

Oxidation was studied of N-acetyl derivatives of cystine, cysteine, methionine and glycyltryptophan employing the myeloperoxidase-Cl--H2O2 system at pH 4.5, 6.0 and 7.0. Moreover, oxidation of pentapeptide composed of Leu-Trp-Met-Arg-Phe-COOH with myeloperoxidase (donor:hydrogen-peroxide oxidoreductase, EC 1.11.1.7) and hypochlorite was also studied. It was found that amino-acid derivatives having an amino group bound to an acetyl residue react with functional groups of the side-chain. The -SH groups of N-acetylcysteine and the -SS- group of cystine oxidize to cysteic acid. Methionine residues oxidize to methionine sulphoxide, and tryptophan residues to a derivative of 2-oxoindolone. The same reaction products were obtained when respective amounts of hypochlorous acid were used instead of myeloperoxidase, Cl- and H2O2. Differences in the stoichiometry of reactions of myeloperoxidase-mediated oxidation and hypochlorite oxidation suggest differences in the reaction mechanisms of both studied systems. Interaction of the studied pentapeptide with myeloperoxidase-Cl(-)-H2O2 system as well as with hypochlorite showed that in the peptide molecule individual amino acids oxidize consecutively according to their susceptibility to oxidation. No splitting of peptide bonds was observed. Therefore, a modified peptide with methionine sulphoxide and and oxidized tryptophan incorporated into the molecule was obtained.