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To study the possible presence of staphylococcal enterotoxins in Manchego-type cheese, milk was inoculated with the enterotoxigenic Staphylococcus aureus collection strains FRI-100, S6, FRI-137, and FRI-472 to a final concentration of 10,000 to 25,000 cfu/ml. Cheese was prepared following the industrial specifications and ripened for 60 d. Batches were prepared with 1 and .1% lactic acid culture and labeled with the abbreviated name of the strain and the concentration of lactic acid culture. Mean staphylococcal counts in .1% lactic bacteria cheeses were usually more than 1 log higher than the corresponding 1% ones. Staphylococcal counts declined markedly after d 35 to 42, and, by the end of ripening, they had disappeared from some cheeses. Enterotoxins were present in five of the cheeses, three prepared with .1% and two with 1% lactic bacteria. Enterotoxins detected were A and D, the enterotoxins most commonly associated with human intoxication. The maximum level of enterotoxin A detected in cheese with strain FRI-100 and with the .1% culture was 222 ng/100 g of cheese; in cheese FRI-100 with 1%, 111 ng/100 g; in cheese S6 with .1%, 769 ng/100 g; and in cheese S6 with 1%, 33 ng/100 g. Maximum level of enterotoxin D detected in cheese FRI-472 with .1% was 38 ng/100 g.

Dissociation of protein-containing structures by modification of protein amino groups with dicarboxylic acid anhydrides is a mild procedure which, in some cases, offers advantages over treatment with alternative dissociating agents, such as urea, guanidine hydrochloride, detergents, high ionic strength, and extremes of pH. In addition to dissociating multimeric proteins and protein aggregates, dicarboxylic acid anhydrides are effective dissociating agents for membrane-bound proteins and nucleoprotein particles. With most dicarboxylic acid anhydrides reviewed, the introduced reagent residues can be eliminated under moderate acid conditions, which allows the purification of unmodified individual components, and the use of diassembly-reconstitution systems valuable for investigating the structural and functional roles played by the individual components of complex particles. Each reagent can be suitable for a particular purpose, depending on the required specificity of the modification and stability of the modified groups. The stability of the acylated amino groups ranges from the very stable succinylated amino groups to the very labile acylation obtained with dimethylmaleic anhydride. Between these extremes, the stability of the modified amino groups decreases stepwise in the following order: maleic, exo-cis-3,6-endoxo-delta 4-tetrahydrophthalic, citraconic, and 3,4,5,6-tetrahydrophthalic anhydride. With respect to the selectivity of the produced modification, little or no modification of hydroxyamino acid and cysteine residues has been observed with dimethylmaleic, exo-cis-3,6-endoxo-delta 4-tetrahydrophthalic, and 3,4,5,6-tetrahydrophthalic anhydrides. With the other reagents, the extent of modification of hydroxyamino acid residues increases in the order citraconic, maleic and succinic anhydride. Citraconic and maleic anhydrides can produce irreversible modification of cysteine residues, the reactivity of sulfhydryl groups being higher with maleic anhydride.

Inhibition of protein synthesis by trichodermol, diacetoxyscirpenol and verrucarin A in cells and spheroplasts of Saccharomyces cerevisiae was investigated. Inhibition was reversible for trichodermol and diacetoxyscirpenol, both drugs being removed from their target site(s) by washing, but was irreversible for verrucarin A. These results are interpreted in relation to variations in chemical structure between these trichothecenes.The 12,13-epoxytrichothecenes (Fig.

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