Akr1 attenuates methylmercury toxicity through the palmitoylation of Meh1 as a subunit of the yeast EGO complex.

BACKGROUND: We previously reported that palmitoyltransferase activity of Akr1 is required for alleviation of methylmercury toxicity in yeast. In this study, we identified a factor that alleviates methylmercury toxicity among the substrate proteins palmitoylated by Akr1, and investigated the role of this factor in methylmercury toxicity. METHODS: Gene disruption and site-directed mutagenesis were used to examine the relationship of methylmercury toxicity and vacuole function. Palmitoylation was investigated using the acyl-biotinyl exchange method. Vacuoles were stained with the fluorescent probe FM4-64. RESULTS: We found that Meh1 (alias Ego1), a substrate protein of Akr1, participates in the alleviation of methylmercury toxicity. Moreover, almost no palmitoylation of Meh1 when Akr1 was knocked out, and mutant Meh1, which is not palmitoylated, did not show alleviation of methylmercury toxicity. The palmitoylated Meh1 was involved in the alleviation of methylmercury toxicity as a constituent of EGO complex which suppresses autophagy. Methylmercury caused vacuole deformation, and this was greater in the yeasts knocking out the EGO complex subunits. 3-Methyladenine, an autophagy inhibitor, suppresses vacuole deformation and cytotoxicity caused by methylmercury. The elevated methylmercury sensitivity by Meh1 knockout almost completely disappeared in the presence of 3-methyladenine. CONCLUSIONS: Akr1 reduces methylmercury toxicity through palmitoylation of Meh1. Furthermore, the EGO complex including Meh1 reduces methylmercury toxicity by suppressing the induction of vacuole deformation caused by methylmercury. GENERAL SIGNIFICANCE: These findings propose that Meh1 palmitoylated by Akr1 may act as a constituent of the EGO complex when contributing to the decreased cytotoxicity by negatively controlling the induction of autophagy by methylmercury.

Interlaboratory Study on Caprolactam Test for Food-Contact Nylon Products.

The Japanese Food Sanitation Law sets a limit on the migration level of caprolactam for food-contacting nylon products. Here, we carried out an interlaboratory study in twenty laboratories to evaluate the performance of the official GC-FID test method and a GC-MS method as an alternative test method to the official method. Each laboratory quantified caprolactam in three test solutions in 20% ethanol as blind duplicates using GC-FID or GC-MS. The official method (GC-FID with absolute calibration) gave trueness, repeatability (RSDr) and reproducibility (RSDr) values of 96-97%, 3.3-5.4% and 4.0-6.7%, respectively. These values met the target criteria (trueness: 80-110%, RSDr: 10%, RSDr: 25%). The performance of the method was further improved by the introduction of heptalactam as an internal standard. As for GC-MS method, some values of the RSDr exceeded 10% when absolute calibration was used. However, when an internal standard was introduced, the trueness, RSDr and RSDr of GC-MS method were all acceptable at 94-96%, 2.0-4.4% and 7.0-9.4%, respectively. Therefore, GC-MS with an internal standard is available as an alternative test method to the official method.

Interlaboratory Study on Volatiles Test for Food-Contacting Polystyrene Products.

Using polystyrene, acrylonitrile-styrene resin and acrylonitrile-butadiene-styrene resin pellets as samples, an interlaboratory study was performed to evaluate the volatiles test method, based on the specifications described in the Japanese Food Sanitation Law for food-contacting polystyrene products. The study was conducted with the participation of twenty-one laboratories. Each laboratory quantified the contents of styrene, toluene, ethylbenzene, isopropylbenzene and propylbenzene in three test pellets using GC-FID, GC-MS or headspace-GC-FID. Statistical analysis revealed that the repeatability (RSDr) and reproducibility (RSDr) were 1.0-2.6 and 2.5-5.5% for the GC-FID method. The values of the performance parameters fulfilled the requirements (RSDr: 10%, RSDr: 25%), and the performance is sufficient for specifications testing. The RSDr and RSDr of results obtained using the GC-MS and HS-GC methods were 1.4-7.8 and 4.9-13%(GC-MS), and 2.0-2.6 and 3.3-6.9%(HS-GC-FID), respectively. The quantified levels were similar to those obtained with GC-FID. The study suggests that the GC-MS and HS-GC methods can be employed as alternative methods to the GC-FID method.

[Interlaboratory Study on Zinc Test for Food-Contact Rubber Products].

Using six kinds of zinc solution in water and 4% acetic acid as samples, an interlaboratory study was performed to evaluate a zinc (Zn) test method for food-contact rubber products, based on the Japanese Food Sanitation Law. Eighteen laboratories participated, and quantified Zn in six test solutions as blind duplicates using flame atomic absorption spectrometry, induced coupled plasma-optical emission spectrometry or induced coupled plasma-mass spectrometry. Statistical analysis revealed that the trueness, repeatability (RSDr) and reproducibility (RSDr) were 97-103%, 0.7-4.9% and 1.7-8.9% by all measuring methods. The values of the performance parameter fulfilled the target value (trueness: 80-110%, RSDr: 10%, RSDr: 25%). The performance of these methods is sufficient for testing the adherence of samples to the specifications.

[Interlaboratory study on migration test of antimony and germanium for food-contact polyethylene terephthalate].

An interlaboratory study was performed to evaluate a migration test method of antimony (Sb) and germanium (Ge), based on the Japanese Food Sanitation Law for food- contact polyethylene terephthalate. Eighteen laboratories participated, and quantified Sb and Ge in three test solutions as blind duplicates using graphite furnace atomic absorption spectrometry (GF-AAS), inductively coupled plasma-optical emission spectrometry (ICP-OES) or induced coupled plasma-mass spectrometry (ICP-MS). Statistical analysis revealed that the trueness, repeatability and reproducibility were 98-107%, 1.7-7.5% and 2.0-18.8% by using GF-AAS and ICP-OES. The performance of these methods is sufficient for testing the specifications. The performance parameters of ICP-MS were 99-106%, 0.7-2.2% and 2.2-10.5%, respectively. ICP-MS is available as an alternative measuring method. However, in some laboratories, the quantitative values of Sb were higher than the addition levels. We found that Sb in working solutions is absorbed on glass vessels. Careful control of concentration in working solutions is required for Sb analysis.

[Interlaboratory study on migration test of cadmium and lead for food contact articles].

An interlaboratory study was performed to evaluate a migration test method of cadmium (Cd) and lead (Pb), based on the Japanese Food Sanitation Law for glassware, ceramicware, enamelware and metal cans. Seventeen laboratories participated, and quantified Cd and Pb in eight test solutions as blind duplicates using flame atomic absorption spectrometry (AAS), graphite furnace atomic absorption spectrometry (GF-AAS), inductively coupled plasma-optical emission spectrometry (ICP-OES) or induced coupled plasma-mass spectrometry (ICP-MS). Statistical analysis revealed that the trueness, repeatability (RSDr) and reproducibility (RSDr) were 93-105%, 0.7-8.4% and 2.6-19.3% by using AAS, ICP-OES and ICP-MS (internal standard method). The performance of these methods is sufficient for testing specifications. However, some of the RSDr values exceeded 10% in GF-AAS, and careful control of accuracy is required.

[Performance comparison of material tests for cadmium and lead in food contact plastics].

Based on the Japanese Food Sanitation Law, the performances of official and alternative material test methods for cadmium (Cd) and lead (Pb) in food contact plastics were compared. Nineteen laboratories participated to an interlaboratory study, and quantified Cd and Pb in three PVC pellets. in the official method, a sample is digested with H2SO4, taken up in HCl, and evaporated to dryness on a water bath, then measured by atomic absorption spectrometry (AAS) or inductively coupled plasma-optical emission spectrometry (ICP-OES). Statistical treatment revealed that the trueness, repeatability (RSDr) and reproducibility (RSDr) were 86-95%, 3.1-9.4% and 8.6-22.1%, respectively. The values of the performance parameters fulfilled the requirements , and the performances met the test specifications. The combination of evaporation to dryness on a hot plate and measurement by AAS or ICP-OES is applicable as an alternative method. However, the trueness and RSDr were inferior to those of the official method. The performance parameters obtained by using the microwave digestion method (MW method) to prepare test solution were better than those of the official method. Thus, the MW method is available as an alternative method. Induced coupled plasma-mass spectrometry (ICP-MS) is also available as an alternative method. However, it is necessary to ensure complete digestion of the sample.