Although exposure of Synechococcus sp. PCC 7942 to iron stress induced the accumulation of the isiA gene product (CP43P P) compared with non-stressed controls, immunodetection of the N-terminus of cytochrome (Cyt) f indicated that iron stress not only reduced the content of the 40 kDa, heme-binding, Cyt f polypeptide by 32% % but it also specifically induced the accumulation of a new, 23 kDa, non-heme-binding, putative Cyt f polypeptide. Concomitantly, iron stress restricted intersystem electron transport based on the in vivo reduction of P700 + , monitored as v vA 820 /A 820 in the presence and absence of electron transport inhibitors, as well as the inhibition of the Emerson enhancement effect on O 2 evolution. However, iron stress appeared to be associated with enhanced rates of PS I cyclic electron transport, low rates of PS I-driven photoreduction of NADP + but comparable rates for PS II+PS I photoreduction of NADP + relative to controls. We hypothesize that Synechococcus sp. PCC 7942 exhibits a dynamic capacity to uncouple PS II and PS I electron transport, which may allow for the higher than expected growth rates observed during iron stress. ß

Photosynthetic acclimation to temperature and irradiance was studied in the filamentous, non-heterocystous cyanobacterium Plectonema boryanum UTEX 485. Growth rates of this cyanobacterium measured at ambient CO2 were primarily influenced by temperature with minimal effects of irradiance. Both growth temperature and irradiance affected linolenic (18:3) and linoleic acid (18:2) levels in the four major lipid classes in an independent but additive manner. In contrast, photosynthetic acclimation was not due to either growth temperature or irradiance per se, but rather, due to the interaction of these environmental factors. P. boryanum grown at low temperature and moderate irradiance mimicked cells grown at high light. Compared to cells grown at either 29 degrees C/150 micromol m(-2) s(-1) (29/150) or 15/10, P. boryanum grown at either 15/150 or 29/750 exhibited: (1) reduced cellular levels of Chl a and phycobilisomes (PBS), and concomitantly higher content of an orange-red carotenoid, myxoxanthophyll; (2) higher light saturated rates (Pmax) when expressed on a Chl a basis but lower apparent quantum yields of oxygen evolution and (3) enhanced resistance to high light stress. P. boryanum grown at 15/150 regained normal blue-green pigmentation within 16 h after a temperature shift to 29 degrees C at a constant irradiance of 150 micromol m(-2) s(-1). DBMIB and KCN but not DCMU and atrazine partially inhibited the change in myxoxanthophyll/Chl a ratio following the shift from 15 to 29 degrees C. We conclude that P. boryanum responds to either varying growth temperature or varying growth irradiance by adjusting the ability to absorb light through decreasing the cellular contents of Chl a and light-harvesting pigments and screening of excessive light by myxoxanthophyll predominantly localized in the cell wall/cell membrane to protect PSII from over-excitation. The possible role of redox sensing/signalling for photosynthetic acclimation of cyanobacteria to either temperature or irradiance is discussed.

These results indicate that the maintenance of Tbdn-1 expression is important for retinal blood vessel homeostasis and for controlling retinal neovascularization in adults. Restoration of Tbdn-1 protein expression and/or activity may provide a novel approach for treating proliferative retinopathies.

The role of growth temperature and growth irradiance on the regulation of the stoichiometry and function of the photosynthetic apparatus was examined in the cyanobacterium Plectonema boryanum UTEX 485 by comparing mid-log phase cultures grown at either 29°C/150 mol m Ϫ2 . The stoichiometry of specific components of the photosynthetic apparatus, such as the ratio of photosystem (PS) I to PSII, phycobilisome size and the relative abundance of the cytochrome b 6 /f complex, the plastoquinone pool size, and the NAD(P)H dehydrogenase complex were regulated by both growth temperature and growth irradiance in a similar manner. This indicates that temperature and irradiance may share a common sensing/signaling pathway to regulate the stoichiometry and function of the photosynthetic apparatus in P. boryanum. In contrast, the accumulation of neither the D1 polypeptide of PSII, the large subunit of Rubisco, nor the CF 1 ␣-subunit appeared to be regulated by the same mechanism. Measurements of P700 photooxidation in vivo in the presence and absence of inhibitors of photosynthetic electron transport coupled with immunoblots of the NAD(P)H dehydrogenase complex in cells grown at either 29°C/750 mol m Ϫ2 s Ϫ1 or 15°C/150 mol m Ϫ2 s Ϫ1 are consistent with an increased flow of respiratory electrons into the photosynthetic intersystem electron transport chain maintaining P700 in a reduced state relative to cells grown at either 29°C/150 mol m Ϫ2 s Ϫ1 or 15°C/10 mol m Ϫ2 s Ϫ1 . These results are discussed in terms of acclimation to excitation pressure imposed by either low growth temperature or high growth irradiance.Cyanobacteria are a large and diverse group of prokaryotes performing oxygenic photosynthesis in a manner similar to green algae and plants. The cyanobacterial photosynthetic apparatus consists of five multiprotein complexes. PSII, cytochrome b 6 f, PSI, and ATP synthase are common to both cyanobacteria and plants. However, the fifth complex, a lightharvesting antenna of PSII, is functionally but not structurally homologous (Gantt, 1994). In cyanobacteria, light harvesting is mediated by phycobilisomes (PBSs), complex protein structures located on the cytoplasmic surface of the thylakoid membranes. The major components of the PBS are the biliproteins, allophycocyanin (AP), phycocyanin (PC), phycoerythrin, and phycoerythrocyanin, with covalently attached bilin chromophores. Different colorless linker polypeptides are specifically associated with each type of phycobiliprotein and function to stabilize the PBS and optimize their absorbance and energy transfer characteristics. The PBSs are composed of two structural domains: an AP core that is in direct contact with the thylakoid membrane and generally six rods of stacked PC and, in some strains, phycoerythrin or phycoerythrocyanin hexamers radiating from the core (Sidler, 1994).Another important distinction between cyanobacteria and chloroplasts is that in cyanobacteria, both respiratory and photosynthetic electron transport chains function within thylakoid membranes, wh...

The efficient extraction of proteins of interest from cells and tissues is not always straightforward. Here we demonstrate the differences in extraction of the focal adhesion protein Kindlin-2 from choriocarcinoma cells using NP-40 and RIPA lysis buffer. Furthermore, we demonstrate the use of a more denaturing urea/thiourea lysis buffer for solubilization, by comparing its effectiveness for solubilization of small heat-shock proteins from smooth muscle with the often utilized RIPA lysis buffer. Overall, the results demonstrate the importance of establishing the optimal lysis buffer for specific protein solubilization within the experimental workflow.