Association by 2,3-dihydroxybenzaldehyde of monomeric phenolase in spinach chloroplasts

In the presence of 5 mM 2,3-dihydroxybenzaldehyde, the monomeric phenolase (MW 36000) of spinach chloroplasts is completely converted to its dimer within 6 hr without significant change in activity. The aldehyde at concentrations higher than 0.25 mM could bring about this conversion after 18 hr treatment. The association of the two monomers becomes tighter with increasing concentration of the aldehyde. The dimer gave rise to a higher MW protein after freezing briefly. Several mono- and dihydroxybenzaldehydes, 2,3-dihydroxybenzoic acid, and o-vanillin did not produce the dimer.     

Diel feeding patterns of the congiopodid fishHypodytes rubripinnis in Aburatsubo Bay,Japan

Diel changes in the feeding intensity and diet composition of the congiopodid fishHypodytes rubriphnnis were studied in Aburatsubo Bay, Miura Peninsula, Japan, on July 24 and 25, 1985. In samples taken at night, the ratio of stomach content weight to body weight was high and the frequency of occurrence of fish with empty stomach was very low, while the reverse was the case in the daytime, suggesting that this species feeds intensively at night, instead of during the day. Gammarids were the most dominant prey and isopods and caprellids were next important. These three prey items accounted for 91% of the total diet by number. The proportion of isopods in the total diet showed the most remarkable diel change. They amounted to about 30% at night, but were not consumed in the daytime.     

Identification of plasmid partition function in coryneform bacteria

We have identified and characterized a partition function that is required for stable maintenance of plasmids in the coryneform bacteria Brevibacterium flavum MJ233 and Corynebacterium glutamicum ATCC 31831. This function is localized to a HindIII-NspV fragment (673 bp) adjacent to the replication region of the plasmid, named pBY503, from Brevibacterium stationis IFO 12144. The function was independent of copy number control and was not associated directly with plasmid replication functions. This fragment was able to stabilize the unstable plasmids in cis but not in trans.     

Conformational states of syntaxin-1 govern the necessity of N-peptide binding in exocytosis of PC12 cells and Caenorhabditis elegans

Syntaxin-1 is the central SNARE protein for neuronal exocytosis. It interacts with Munc18-1 through its cytoplasmic domains, including the N-terminal peptide (N-peptide). Here we examine the role of the N-peptide binding in two conformational states (“closed” vs. “open”) of syntaxin-1 using PC12 cells and Caenorhabditis elegans. We show that expression of “closed” syntaxin-1A carrying N-terminal single point mutations (D3R, L8A) that perturb interaction with the hydrophobic pocket of Munc18-1 rescues impaired secretion in syntaxin-1–depleted PC12 cells and the lethality and lethargy of unc-64 (C. elegans orthologue of syntaxin-1)-null mutants. Conversely, expression of the “open” syntaxin-1A harboring the same mutations fails to rescue the impairments. Biochemically, the L8A mutation alone slightly weakens the binding between “closed” syntaxin-1A and Munc18-1, whereas the same mutation in the “open” syntaxin-1A disrupts it. Our results reveal a striking interplay between the syntaxin-1 N-peptide and the conformational state of the protein. We propose that the N-peptide plays a critical role in intracellular trafficking of syntaxin-1, which is dependent on the conformational state of this protein. Surprisingly, however, the N-peptide binding mode seems dispensable for SNARE-mediated exocytosis per se, as long as the protein is trafficked to the plasma membrane.     

Constitution of inactive phenolase-inhibitor complex in spinach chloroplasts

From inactive phenolase-inhibitor complex of spinach chloroplasts, the inhibitor is liberated with ethyl acetate. The complex is re-constituted from its two components by freezing, and can be activated at elevated temperatures. The inhibitor seems to be a volatile acid, and on freezing, propionic, butyric and valeric acids can reduce the enzyme activity greatly.