Comparison of radioimmunoassay and enzyme-linked immunosorbent assay for determining aflatoxin M1 in milk

Using a highly specific antibody against aflatoxin M1, a radioimmunoassay (RIA) and an enzyme-linked immunosorbent assay (ELISA) were developed for the quantitation of M1 in milk. RIA was sensitive in the range of 5-50 ng per assay but was subject to interference by whole milk. Extraction and cleanup were therefore necessary for the detection of M1 in milk at 0.5 ng/mL. An ELISA procedure was developed by using an aflatoxin M1-carboxymethyl-horseradish peroxidase conjugate as the ligand. Competitive assays revealed that this system was relatively more sensitive for M1 than for B1, and had a much lower degree of cross-reactivity for aflatoxins B2, G1, G2, B2a, and aflatoxicol. As low as 0.25 ng M1/mL in artificially contaminated milk (raw, whole, skim) could be detected by ELISA in 3 h without extraction or cleanup. Because of its simplicity, sensitivity, and specificity, ELISA is the preferred method for monitoring aflatoxin M1 in milk.

Preparation of protein conjugates via intermolecular disulfide bond formation

Conjugates of two unlike proteins can be prepared via the intermolecular disulfide interchange reaction, namely, protein A containing thiol groups reacts with protein B containing 4-dithiopyridyl groups to yield a conjugate with the release of 4-thiopyridone. Thiol groups can be introduced into proteins upon amidination with methyl 3-mercaptopropionimidate ester or 2-iminothiolane, and 4-dithiopyridyl groups can be introduced into proteins with these same reagents in the presence of 4,4'-dithiodipyridine. 2-Iminothiolane is stable on storage in contrast to the known lability of imidate esters; therefore 2-iminothiolane is a more convenient reagent for the modification of protein than are the imidate esters. All the reactions can be carried out easily under mild conditions in good yields. Conjugates of bovine plasma albumin with itself, ribonuclease, or a copolymer of D-glutamic acid and D-lysine and of sheep antibody and horseradish peroxidase were prepared with modified proteins containing an average of 1 to 5 thiol or dithiopyridyl groups per mol. These conjugates formed mainly dimers, trimers, and tetramers. The peroxidase labeled antibody retained more than 80% of its enzymatic and antigenic binding activities.

Isolation and identification of the major metabolite of albuterol in human urine

The major urinary metabolite of albuterol in man was isolated and purified by ion-exchange chromatography and countercurrent distribution. On the basis of proton magnetic resonance, infrared, and mass-spectral analysis, enzymic hydrolysis, and assay of inorganic sulfate after acid hydrolysis, the metabolite has been identified as the 4'-O-sulfate ester of albuterol.

Population growth and environmental problems in Taiwan (Formosa): a case-study

Taiwan has the highest population density in the world today. The population growth-rate has been decreasing linearly since 1951, but the present growthrate of 2% is still much too high to lessen the population pressure. With the area of agricultural land severly limited, the agricultural sector of Taiwan can no longer absorb extra farm labourers without sacrificing the productivity of each farm labourer.

In order to feed the growing population, the high productivity of a rice paddy has been maintained by applying ever-increasing amounts of chemical fertilizers and pesticides, which in turn cause many pollution problems. Moreover the rapid growth of industries, which are mainly financed by outside capital, causes the expansion and congestion of the cities along with all sorts of pollution problems (air pollution of cities, water pollution of rivers, harbours, coastal waters, etc.)

The heavy dependence on imported energy (70% of the total energy consumption) and on trade with Japan and the United States, puts Taiwan in a vulnerable position with regard to fluctuations in the world economy. The ever-increasing population density, and the demands of a higher per caput consumption on the limited natural resources, risk leading to economic inadequacy and ecological degradation. Such a situation could endanger our industrial civilization more widely.