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Despite the very small amounts of cytochrome P450 (P450, CYP) enzymes expressed in different areas and cell populations of the brain as compared with the liver, there is significant evidence for their specific involvement in brain development, function and plasticity. Nevertheless, the current discussion about occurrence and importance of cerebral cytochrome P450s is determined by inconsistent interpretations of their function in general and with respect to single isoforms. Continuing a series of publications about brain P450 isoforms, we now present evidence for the constitutive expression of CYP2B1 and CYP2B2 mRNAs in rat brain. Immunocytochemical and non-radioactive in situ hybridization studies revealed the same expression pattern throughout the brain predominantly in neuronal populations, but to some extent in astrocytes of corpus callosum and olfactory bulb. The well known testosterone-metabolizing capacity and the presence of CYP2B isoforms shown in steroid hormone-sensitive areas and neurones (e.g. hippocampus) clarify the significance of isoforms like CYP2B1 and CYP2B2 for impairment of steroid hormone actions by P450 inducing environmental substances. We argue that cerebral P450 isoforms which are induced by xenobiotics and are able to metabolize these as well as endogenous substrates help us to understand fundamental aspects of brain's functioning. [ABSTRACT FROM AUTHOR]

The ripening process in fruits of A. commutatum is characterized by clearly distinguishable developmental stages of their pericarp plastids. With respect to predominant pigments and ultrastructural features the following scheme is proposed: 1. The green stage with a tendency to thylakoid degeneration and plastoglobule formation leads to 2. the yellow stage. An increasing number of globules, mostly being membrane associated, are converted to tubules. In this stage, the main pigments are β-carotene and cryptoxanthine. The development of membraneous invaginations from the inner plastid envelope leads to 3. the red stage. Concomitantly with lycopene synthesis and incorporation, these envelope-derived membranes expand and become electron dense (after KMnO treatment), but maintain their triple-layered structure. Chromoplasts of deep red coloured fruits (1,400 μg lycopene g dry wt) contain lycopene crystals within the lumina of membraneous sacs which are also derived from the inner envelope membrane. The molar ratio between the three main pigments β-carotene, cryptoxanthine, and lycopene is about 1∶1∶10 in this final state. GA/OsO fixation is unable to stabilize the 'lycopenic' structures (membranes as well as crystals). [ABSTRACT FROM AUTHOR]