Two distinct O-methyltransferases in aflatoxin biosynthesis

The substances belonging to the sterigmatocystin group bear a close structural relationship to aflatoxins. When demethylsterigmatocystin (DMST) was fed to Aspergillus parasiticus NIAH-26, which endogenously produces neither aflatoxins nor precursors in YES medium, aflatoxins B1 and G1 were produced. When dihydrodemethylsterigmatocystin (DHDMST) was fed to this mutant, aflatoxins B2 and G2 were produced. Results of the cell-free experiment with S-adenosyl-[methyl-3H]methionine showed that first the C-6-OH groups of DMST and DHDMST are methylated to produce sterigmatocystin and dihydrosterigmatocystin (O-methyltransferase I) and then the C-7-OH groups are methylated to produce O-methylsterigmatocystin (OMST) and dihydro-O-methylsterigmatocystin (DHOMST) (O-methyltransferase II). However, no methyltransferase activity was observed when either OMST, DHOMST, 5,6-dimethoxysterigmatocystin, 5-methoxysterigmatocystin, or sterigmatin was incubated with the cell extract. Treatment of the cell extract with N-ethylmaleimide inhibited O-methyltransferase I activity but not that of O-methyltransferase II. Furthermore, these O-methyltransferases were different in their protein molecules and were involved in both the reactions from DMST to OMST and DHDMST to DHOMST. The reactions described in this paper were not observed when the same mold had been cultured in YEP medium.     

Fluctuation of body temperature and cuckoo brood parasitism

Body temperatures of 11 bird species, including cuckoos, were measured in an artificial meteorological room. Ratios of change in body temperature to that in air temperature were thereby obtained for each species. Cuckoos demonstrate a remarkably high value, indicating a particularly low ability to regulate body temperature. Viewed in this light, the cuckoo's parasitic behavior is very likely an adaptation to overcome a physiological disadvantage. This in turn might be expected to reinforce delay in evolution of temperature homeostasis.     

Genetic structure of the IncN plasmid N3

N3, a plasmid of incompatibility group N (IncN) was mapped by cleavage with restriction endonucleases. The restriction fragments were cloned into vector plasmids. All of the genes unique to IncN plasmids such as specific replication machinery, a restriction-modification system, and repair functions were located on a large portion which had no cleavage sites for many of the site-specific six base-identifying restriction endonucleases tested.     

Structure of triphosphonoglycosphingolipid containing N-acetylgalactosamine 6-O-2-aminoethylphosphonate in the nervous system of Aplysia kurodai

A phosphonoglycosphingolipid, named F-21, was found in the nervous system of Aplysia kurodai by two-dimensional thin-layer chromatography (Abe, S., Araki, S., and Satake, M. (1986) Biomed. Res. (Tokyo) 7, 47-51). F-21 was isolated from the nervous tissue of Aplysia in this study, and its chemical structure was characterized as follows, where 2-AEP is 2-aminoethylphosphonate. (Formula; see text) The major aliphatic components of the ceramide portion were palmitic acid (75%), stearic acid (22%), octadeca-4-sphingenine (43%), and anteisononadeca-4-sphingenine (54%). Some information on the steric interactions in the sugar moiety was obtained by NMR spectroscopy. The ring protons of the internal galactose, H1, H3, and H4 and the H3 of the side chain galactose were shifted, as compared to the corresponding protons of dephosphonylated F-21. This may indicate the interactions between the 2-AEP residue of N-acetylgalactosamine and the internal galactose and between the N-acetyl group of N-acetylgalactosamine and the side chain galactose, implying a sterically restricted and unique structure that may relate to some biological functions of F-21.