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Changes in protein composition were noted when heterocysts of Anabaena sp. strain CA were isolated from filaments grown in 1% CO2-99% N2 and subsequently exposed to oxygen. Immunospecific Western blot analysis showed that the Fe protein of nitrogenase is altered. In cells grown under microaerobic conditions, the Fe protein was found in a form with an apparent molecular weight of 30,000. Exposure to oxygen caused a shift in the migration of this polypeptide to a position corresponding to an apparent molecular weight of 31,500. This modification was reversible upon removal of oxygen from the culture. Chloramphenicol did not inhibit the alteration in either direction. Suppression by ammonium nitrate of the recovery of nitrogenase activity from the effects of oxygen did not prevent the alteration of the protein. Other inhibitors of nitrogenase activity, (metronidazole, carbonyl cyanide m-chlorophenylhydrazone, and phenazine methosulfate) were tested for their effect on Fe protein modification. Alteration of the Fe protein may relate to the protection of nitrogenase from the deleterious effects of oxygen.

The cyanobacterium Agmenellum quadruplicatum PR-6 (Synechococcus sp PCC 7002) was grown turbidostatically in white light at three levels of irradiance: 20, 200, and 1260 microeinsteins per square meter per second. Phycobilisomes were isolated from each culture and analyzed by absorbance, gel electrophoresis, and electron microscopy. The ratio of phycocyanin to allophycocyanin decreased 1.8-fold from the lowest to highest irradiance. This change was due entirely to an approximately 2.5-fold decrease in one structural unit of rod domains, the complex of phycocyanin, and a 33-kilodalton linker polypeptide (LR33). For a given irradiance, phycobilisomes from cells grown on ammonium as the nitrogen source had 10 to 20% more phycocyanin than those from nitrate cultures. Total RNA was isolated from all cultures and probed with gene fragments specific to phycocyanin and allophycocyanin subunits and LR33. The relative level of RNAs encoding phycocyanin and allophycocyanin was found to vary with light intensity in parallel with the phycobiliprotein ratio. Hence, the light-harvesting capacity of phycobilisomes is directly regulated by relative levels of phycobiliprotein mRNA. The LR33 transcript occurs as a 3' extension on about 10% of phycocyanin transcripts. The ratio of RNA encoding LR33 to that encoding phycocyanin did not vary with irradiance, although the protein ratio changed 1.7-to twofold between extremes. Based on these and other observations, we propose that the LR33 protein is constitutively synthesized at a rate higher than that required to complex with available phycocyanin.The cyanobacterium Agmenellum quadruplicatum (Synechococcus sp PCC 7002) was chosen for this study. The phycobilisomes of this organism are well described in terms ofoverall structure and the function ofindividual polypeptide components (reviewed in refs. 2 and 6). The major components of this complex are the pigmented proteins, PC' and AP. The former is localized in rod substructures, where it is bound to linker polypeptides called LRC29, LR33, and LR9. Rods are linked to a central core domain by LRC29. The core contains AP and its associated linker polypeptides.The genes encoding the a and 13 subunits of PC (cpcA and cpcB, respectively) are linked in tandem with those encoding LR33 (cpcC) and LR9 (cpcD) (7-9, 20) (Fig. 4). Genes encoding AP a and ,B subunits (apcA and apcB, respectively) and one linker polypeptide (LC8.5) are similarly clustered (4). Transcripts encoding these cpc and apc loci have been mapped (12). The major transcript of each locus encodes only the a and ,B subunits of the respective phycobiliproteins. Minor transcripts extend further in the 3' direction to encode linker polypeptides. Having this knowledge of phycobilisome structure and gene organization in A. quadruplicatum, we could readily investigate responses to changes in light intensity.In addition to irradiance, we simultaneously examined the effect of nitrogen source on phycobilisome structure. This is of interest because phycobiliproteins are strongly...

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With deterioration of the wild population over the last two decades, captive reproduction of black rhinoceros has become a high priority for zoological gardens. Several reproductive parameters of female black rhinoceros were analyzed with data from the international studbook, and compared to data from field studies. These analyses yielded comparisons for ages of females at first calving, length of birth intervals, and span of reproductive life, The implications for rhino productivity are discussed, and some suggestions for increasing productivity are presented. o 1992 WiIey-Liss, Inc.