Soluble cytochrome c-554, CycA, is not essential for photosynthetic electron transfer in Chlorobium tepidum

We constructed a mutant lacking soluble cytochrome c-554 (CycA) by disruption of the cycA gene in the green sulfur bacterium Chlorobium tepidum. The mutant grew phototrophically with a growth rate slower than that of the wild type, suggesting that CycA is not essential for photosynthetic electron transfer even though CycA is known to work as an electron donor to the reaction center. The re-reduction of photo-oxidized cytochrome c(z) by quinol oxidoreductase was inhibited almost completely by the addition of stigmatellin in the mutant cells. This result indicates that, in the mutant cells, the linear electron transfer can occur from the quinol oxidoreductase to cytochrome c(z), and to reaction center P840 with no participation of CycA.     

Pheophytinization kinetics of chlorophyll c under weakly acidic conditions: Effects of acrylic acid residue at the 17-position

Pheophytinization of chlorophyll (Chl) c₁, which was isolated from the diatom Chaetoceros gracilis, was kinetically analyzed under weakly acidic conditions, and was compared with that of protochlorophyllide (PChlide) a and chlorophyllide (Chlide) a. Chl c₁ possessing a trans-acrylic acid residue at the 17-position exhibited slower pheophytinization kinetics than PChlide a and Chlide a, both of which possessed a propionic acid residue at the same position. The difference in pheophytinization properties between Chl c₁ and (P)Chlide a was ascribable to the electronegativity of the 17-substituent in Chl c₁ larger than that of (P)Chlide a due to the C17¹–C17² double bond with the conjugated 17²-carboxy group in Chl c₁. Demetalation kinetics of PChlide a was slower than that of Chlide a, which originated from the effect of the π-macrocyclic structures.     

Chlorophyllide a Oxidoreductase Works as One of the Divinyl Reductases Specifically Involved in Bacteriochlorophyll a Biosynthesis

Bacteriochlorophyll a is widely distributed among anoxygenic photosynthetic bacteria. In bacteriochlorophyll a biosynthesis, the reduction of the C8 vinyl group in 8-vinyl-chlorophyllide a is catalyzed to produce chlorophyllide a by an 8-vinyl reductase called divinyl reductase (DVR), which has been classified into two types, BciA and BciB. However, previous studies demonstrated that mutants lacking the DVR still synthesize normal bacteriochlorophyll a with the C8 ethyl group and suggested the existence of an unknown “third” DVR. Meanwhile, we recently observed that chlorophyllide a oxidoreductase (COR) of a purple bacterium happened to show the 8-vinyl reduction of 8-vinyl-chlorophyllide a in vitro. In this study, we made a double mutant lacking BciA and COR of the purple bacterium Rhodobacter sphaeroides in order to investigate whether the mutant still produces pigments with the C8 ethyl group or if COR actually works as the third DVR. The single mutant deleting BciA or COR showed production of the C8 ethyl group pigments, whereas the double mutant accumulated 8-vinyl-chlorophyllide, indicating that there was no enzyme other than BciA and COR functioning as the unknown third DVR in Rhodobacter sphaeroides (note that this bacterium has no bciB gene). Moreover, some COR genes derived from other groups of anoxygenic photosynthetic bacteria were introduced into the double mutant, and all of the complementary strains produced normal bacteriochlorophyll a. This observation indicated that COR of these bacteria performs two functions, reductions of the C8 vinyl group and the C7=C8 double bond, and that such an activity is probably conserved in the widely ranging groups.     

Evidence for existence of various homologues and analogues of platelet activating factor in a lipid extract of bovine brain

Vasodepressor phospholipid with platelet-aggregating activity was highly purified from a lipid extract of bovine brain and subjected to field desorption-mass spectrometry. It was further analyzed by gas-liquid chromatography-mass spectrometry after hydrolysis with phospholipase C and conversion to tert-butyldimethylsilyl derivatives. Results indicated the presence of four species of platelet activating factor (1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF) and ten acyl analogues of PAF. The acyl analogues of PAF included species having an sn-2-propionyl or sn-2-butyryl group, which have not been previously detected in natural sources. The total amount of acyl analogues of PAF was much higher than that of PAF.     

Novel molecular analogues of phosphatidylcholines in a lipid extract from bovine brain: 1-long-chain acyl-2-short-chain acyl-sn-glycero-3-phosphocholines

A vasodepressor phospholipid fraction named Depressor-IA from a bovine brain lipid extract was analyzed by capillary gas-liquid chromatography-mass spectrometry as tert-butyldimethylsilyl derivatives after hydrolysis with phospholipase C. Results show that Depressor-IA is a mixture of 3 platelet-activating factors and 17 1-acyl analogues. Three platelet-activating factors having sn-1-O-hexadecyl, octadecyl, and octadecenyl groups were suggested to account for the hypotensive activity of Depressor-IA, although the total amount of 1-acyl analogues of platelet-activating factor was much more than that of platelet-activating factor in the purified Depressor-IA. 1-Long-chain acyl-2-short-chain acyl-glycero-3-phosphocholines identified in Depressor-IA included novel molecular analogues having sn-2-propionyl, acryloyl, butyryl, valeryl, caproyl, and hepatonoyl groups.