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We have prepared a diluted system of Co3O4 nanocrystals dispersed in nonmagnetic SiO2 by heating an MCM-41 molecular sieve soaked in 0.075 mol/L CoCl2 aqueous solution in flowing oxygen at 300 °C for 3 h. Transmission electron microscopy showed that fine particles of about 3 nm exhibiting the (220) and (331) lattice fringes of the Co3O4 crystal distribute randomly in amorphous SiO2. Magnetic measurements using a SQUID magnetometer suggested the presence of quantum resonant spin tunneling of intraparticle superparamagnetic moments below the blocking temperature. The maximum points in the ac susceptibility shifted toward higher temperature from ≈3 to ≈5 K with increasing the frequency from ≈10-2 to ≈103 Hz. There were no divergent peaks above 1.7 K in the nonlinear susceptibility. The field dependent magnetization from 0 to ≈20 kG showed a small hysteresis loop at 2 K, whereas there were no hysteresis loops at both 5 and 10 K. The diluted Co3O4 nanocrystals is a new and ideally suitable material for the study of macroscopic magnetic quantum effects.

Pichia pastoris and Hansenula polymorpha are methylotrophic yeasts capable of utilizing methanol, as a sole source of carbon and energy. Growth of these yeast species on methanol requires the synthesis of cytosolic and peroxisomal enzymes combined with the proliferation of peroxisomes. Peroxisomes are also abundantly present in the alkane-utilizing yeast Yarrowia lipolytica upon growth of cells on oleic acid. This feature has made these yeast species attractive model systems to dissect the molecular mechanisms controlling peroxisome biogenesis. We have found that upon glucose- or ethanol-induced catabolite inactivation, metabolically superfluous peroxisomes are rapidly and selectively degraded within the vacuole by a process called pexophagy, the selective removal of peroxisomes by autophagy-like processes. Utilizing several genetic screens, we have identified a number of genes that are essential for pexophagy. In this review, we will summarize our current knowledge of the molecular events of pexophagy.