Grouped sequential exploitation of food patches in a flock feeder,the feral pigeon

Feral and laboratory flocks of rock doves ($\text{Columba}$$\text{livia}$) show a pattern of grouped sequential exploitation when simultaneously presented with two dispersed, depleting patches of seed. This behavior contrasts with the ideal free distribution pattern shown when patches are small and concentrated. Grouped sequential exploitation consists of two phases: all pigeons first land together and feed at one patch, then leave one by one for the other patch. Departure times of individuals for the second patch are correlated with feeding rate at patch 1, which is in turn correlated with position in the dominance hierarchy. The decision to switch from patch 1 to patch 2 improves individual feeding rates in all cases, but is done slightly later than it should according to optimal foraging theory.     

Cardiolipin biosynthesis and remodeling enzymes are altered during development of heart failure

Cardiolipin (CL) is responsible for modulation of activities of various enzymes involved in oxidative phosphorylation. Although energy production decreases in heart failure (HF), regulation of cardiolipin during HF development is unknown. Enzymes involved in cardiac cardiolipin synthesis and remodeling were studied in spontaneously hypertensive HF (SHHF) rats, explanted hearts from human HF patients, and nonfailing Sprague Dawley (SD) rats. The biosynthetic enzymes cytidinediphosphatediacylglycerol synthetase (CDS), phosphatidylglycerolphosphate synthase (PGPS) and cardiolipin synthase (CLS) were investigated. Mitochondrial CDS activity and CDS-1 mRNA increased in HF whereas CDS-2 mRNA in SHHF and humans, not in SD rats, decreased. PGPS activity, but not mRNA, increased in SHHF. CLS activity and mRNA decreased in SHHF, but mRNA was not significantly altered in humans. Cardiolipin remodeling enzymes, monolysocardiolipin acyltransferase (MLCL AT) and tafazzin, showed variable changes during HF. MLCL AT activity increased in SHHF. Tafazzin mRNA decreased in SHHF and human HF, but not in SD rats. The gene expression of acyl-CoA: lysocardiolipin acyltransferase-1, an endoplasmic reticulum MLCL AT, remained unaltered in SHHF rats. The results provide mechanisms whereby both cardiolipin biosynthesis and remodeling are altered during HF. Increases in CDS-1, PGPS, and MLCL AT suggest compensatory mechanisms during the development of HF. Human and SD data imply that similar trends may occur in human HF, but not during nonpathological aging, consistent with previous cardiolipin studies.     

Autocatalytic processing of the streptococcal cysteine protease zymogen: processing mechanism and characterization of the autoproteolytic cleavage sites.

The autocatalytic processing of the streptococcal cysteine protease zymogen (proSCP) to active streptococcal cysteine protease (SCP) was investigated in vitro using purified protein from Streptococcus pyogenes strain B220. It was found that the autocatalytic maturation of the zymogen proceeds through the sequential appearance of at least six intermediates, five of which were characterized through a combination of N-terminal sequencing and MS. Intermediates were identified as resulting from cleavages after Lys26, Asn41, Lys101, Ala112, and Lys118. Time-course studies of the proSCP processing gave a sigmoidal activity profile and indicated that proSCP catalyses its own transformation, mainly via an intermolecular processing mechanism. A similar sequential appearance of intermediates was observed when inactive Cys192Ser proSCP was treated with native, enzymatically active SCP, thus demonstrating that the maturation can exclusively proceed by a bimolecular mechanism. It was shown that proSCP, but not mature SCP, immobilized on a Sepharose resin is capable of liberating itself from the column, indicating that the zymogen is also capable of intramolecular processing. In order to test whether the amino acid sequences at the processing sites could be used for developing new, specific substrates, 3-amino benzoic acid octapeptide derivatives based on all five characterized amino acid sequences from the autoprocessing cleavage sites were synthesized and tested for activity. The 3-amino benzoic acid derivatives have kcat/KM values ranging from 1200 to 7700.M-1.s-1, making them very good endopeptidase substrates for SCP.