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Between 1996 and 1998, 580 litres of milk in Mexico were surveyed for aflatoxin B1 (AFB1) and its metabolite aflatoxicol (AFL), which are mutagenic and carcinogenic mycotoxins that interconvert AFB1-AFL-AFB1. The seven most consumed brands from different regions of Mexico included pasteurized and ultrapasteurized milk with four different fat levels: whole fat (28-33 g l-1), half-skimmed (10-20 g l-1), light (1-4 g l-1) and with vegetable oil (33 g l-1). Aflatoxins in each sample were concentrated with total aflatoxin immunoaffinity columns and quantitated by high-performance liquid chromatography. A milk sample was considered contaminated if it contained ≥0.05 μg l-1 AFL. Pasteurization and ultrapasteurization of milk did not control contamination with AFL, which was present in 13% of samples at ≥0.05 μg l-1 and in 8% at ≥0.5 μg l-1, with a range of AFL from 0 to 12.4 μg l-1. AFB1 was present mainly in traces (0-0.4 μg l-1). The safest milk in relation to AFL contamination was imported milk powder with vegetable oil. There was a significant correlation between contamination of milk with AFL and the autumn (p<0.0002); the fat content was not significant.

The NADPH oxidase of phagocytes generates microbicidal oxidants in response to a variety of stimuli. Its activation and assembly involve multiple SH3 domain interactions among several oxidase components. Here we present evidence that the cytosolic oxidase-associated protein, p40(phox), mediates down-regulation of NADPH oxidase through interactions with its SH3 domain. Recombinant p40(phox) was produced in several eukaryotic expression systems (insect, mammalian, and yeast) to explore its role in oxidase function in relation to domains involved in interactions with other factors, p47(phox) and p67(phox). p40(phox) inhibited oxidase activity in vitro when added to neutrophil membranes and recombinant p47(phox), p67(phox), and p21rac. Co-transfection of p40(phox) into K562 cells resulted in significant decreases ( approximately 40%) in whole cell oxidase activity. Furthermore, the isolated SH3 domain of p40(phox) was even more effective in inhibiting whole cell oxidase activity, consistent with experiments showing that this domain binds to the same proline-rich target in p47(phox) (residues 358-390) that interacts with p67(phox). In contrast, deletion of the carboxyl-terminal domain of p40(phox) that binds to p67(phox) did not relieve its oxidase inhibitory effects. Thus, p40(phox) appears to down-regulate oxidase function by competing with an SH3 domain interaction between other essential oxidase components.

Src homology 3 (SH3) domains mediate specific protein‐protein interactions crucial for signal transduction and protein subcellular localization. Upon phagocyte stimulation, two SH3 domain‐containing cytosolic components of the NADPH oxidase, p47phox and p67phox, are recruited to the membrane where they interact with flavocytochrome b558 to form an activated microbicidal oxidase. Deletion analysis of p47phox and p67phox in transfected K562 cells demonstrated multiple SH3‐mediated interactions between p47phox and the transmembrane flavocytochrome b558 and also between the cytosolic components themselves. The core region of p47phox (residues 151–284), spanning both SH3 domains, was required for flavocytochrome‐dependent translocation and oxidase activity in whole cells. Furthermore, translocation of p67phox occurred through interactions of its N‐terminal domain (residues 1–246) with p47phox SH3 domains. Both of these interactions were promoted by PMA activation of cells and were influenced by the presence of other domains in both cytosolic factors. Deletion analysis also revealed a third SH3 domain‐mediated interaction involving the C‐termini of both cytosolic factors, which also promoted p67phox membrane translocation. These data provide evidence for a central role for p47phox in regulation of oxidase assembly through several SH3 domain interactions.

A widely useful method for estimating background variation in field experiments would provide experimenters with a diagnostic tool that could be used to reveal trials for which customary design‐based analyses are inadequate. Such a diagnostic tool would provide reassurance for cases suited for customary analyses and would signal a need for corrective analyses when plot to plot variation has not been properly accounted for. This paper is an early step in the search for such a widely useful diagnostic tool. It examines the performance of a number of methods that have been proposed for describing plot to plot variation and explores the effectiveness of these methods over widely different data sets from uniformity trials. Methods were assessed primarily on the basis of consistency of providing residual mean squares usable as a diagnostic measure of background variation. In addition, methods were compared in terms of how well they described plot to plot variation (R2for estimated and observed responses). Results obtained made it clear that the suitability of a method forestimating background variation must be evaluated over a number of different trials, including trials sensitive to block size and orientation. Most methods performed well in at least one or two trials. Few were generally effective. Preliminary indications were that the Best Blocks of Two Method was most generally useful and that Polynomial Regressions and the Modified Papadakis method were promising. The versions used of the following methods were not consistently effective in estimating background variation: Rows and Columns, Ordinary Papadakis, Fourier Analysis and Inverse Polynomial.

The delineation of molecular structures that dictate Src homology 3 (SH3) domain recognition of specific proline-rich ligands is key to understanding unique functions of diverse SH3 domain-containing signalling molecules. We recently established that assembly of the phagocyte NADPH oxidase involves multiple SH3 domain interactions between several oxidase components (p47phox, p67phox, and p22phox). p47phox was shown to play a central role in oxidase activation in whole cells by mediating interactions with both the transmembrane component p22phox and cytosolic p67phox. To understand the specific roles of each SH3 domain of p47phox in oxidase assembly and activation, we mutated critical consensus residues (Tyr167 or Tyr237-->Leu [Y167L or Y237L], W193R or W263R, and P206L or P276L) on each of their binding surfaces. The differential effects of these mutations indicated that the first SH3 domain is responsible for the p47phox-p22phox interaction and plays a predominant role in oxidase activity and p47phox membrane assembly, while the second p47phox SH3 domain interacts with the NH2-terminal domain of p67phox. Binding experiments using the isolated first SH3 domain also demonstrated its involvement in intramolecular interactions within p47phox and showed a requirement for five residues (residues 151 to 155) on its N-terminal boundary for binding to p22phox. The differential effects of nonconserved-site mutations (W204A or Y274A and E174Q or E244Q) on whole-cell oxidase activity suggested that unique contact residues within the third binding pocket of each SH3 domain influence their ligand-binding specificities.