The effect of recombinant caspase 3 on myofibrillar proteins in porcine skeletal muscle

The objective of this study was to investigate the potential role of the caspase protease family in meat tenderisation by examining if caspase 3 was capable of causing myofibril protein degradation. Full-length human recombinant caspase 3 (rC3) was expressed in Escherichia coli and purified. The rC3 was active in the presence of myofibrils isolated from porcine longissimus dorsi muscle (LD) and retained activity in a buffer system closely mimicking post mortem conditions. The effect of increasing concentrations of rC3, incubation temperature, as well as incubation time on the degradation of isolated myofibril proteins were all investigated in this study. Myofibril protein degradation was determined by SDS-PAGE and Western blotting. There was a visible increase in myofibril degradation with a decrease in proteins identified as desmin and troponin I and the detection of protein degradation products at approximately 32, 28 and 18 kDa with increasing concentrations of rC3. These degradation products were analysed using MALDI-TOF mass spectrometry and identified to occur from the proteolysis of actin, troponin T and myosin light chain, respectively. The production of these degradation products was not inhibited by 5 mM EDTA or semi-purified calpastatin but was inhibited by the caspase-specific inhibitor Ac-DEVD-CHO. The temperature at which isolated myofibrils were incubated with rC3 was also found to affect degradation, with increasing incubation temperatures causing increased desmin degradation and cleavage of pro-caspase 3 into its active isoform. Incubation of isolated myofibrils at 4°C for 5 days with rC3 resulted in the visible degradation of a number of myofibril proteins including desmin and troponin I. This study has shown that rC3 is capable of causing myofibril degradation, hydrolysing myofibril proteins under conditions that are similar to those found in muscle in the post mortem conditioning period.     

Antigen recognition in the female reproductive tract. II. Endocytosis of horseradish peroxidase by Langerhans cells in murine vaginal epithelium.

Previous studies have shown that dendritic cells in the murine vaginal epithelium at diestrus and metestrus can endocytose intravaginally administered soluble protein tracers, but the identity of the dendritic cells was not established. In the investigation reported here, we used a combination of histochemistry and transmission electron microscopy to study the endocytosis of exogenous horseradish peroxidase by vaginal dendritic cells and to identify these cells as Langerhans' cells on the basis of their cellular associations, ultrastructural morphology, and the presence of Langerhans' cell granules.     

A kinetic study of the folding of nuclease B, a possible precursor of staphylococcal nuclease A.

Nuclease B, which contains an additional flexible amino acid sequence of 19 amino acid residues bound to the NH2-terminus of nuclease A, an extracellular nuclease of Staphylococcus aureus, has been investigated in order to determine the influence of the extra residues on the refolding of the nuclease A portion from the acid denaturated state by monitoring the change in tryptophan fluorescence using a stopped-flow technique. It was found that the kinetic parameters of this refolding is similar within experimental error for nuclease A and nuclease B for the entire course (up to 40 s) studied. Therefore, the extra residues do not appear to have any detectable effect on the dynamic events involved in the refolding process. Thus, the folding of the nuclease A portion of nuclease B appears to be thermodynamically and kinetically independent of the 19 residues at the amino-terminus.     

Virtual Reconstruction and Prey Size Preference in the Mid Cenozoic Thylacinid,Nimbacinus dicksoni (Thylacinidae,Marsupialia)

Thylacinidae is an extinct family of Australian and New Guinean marsupial carnivores, comprizing 12 known species, the oldest of which are late Oligocene (∼24 Ma) in age. Except for the recently extinct thylacine (Thylacinus cynocephalus), most are known from fragmentary craniodental material only, limiting the scope of biomechanical and ecological studies. However, a particularly well-preserved skull of the fossil species Nimbacinus dicksoni, has been recovered from middle Miocene (∼16-11.6 Ma) deposits in the Riversleigh World Heritage Area, northwestern Queensland. Here, we ask whether N. dicksoni was more similar to its recently extinct relative or to several large living marsupials in a key aspect of feeding ecology, i.e., was N. dicksoni a relatively small or large prey specialist. To address this question we have digitally reconstructed its skull and applied three-dimensional Finite Element Analysis to compare its mechanical performance with that of three extant marsupial carnivores and T. cynocephalus. Under loadings adjusted for differences in size that simulated forces generated by both jaw closing musculature and struggling prey, we found that stress distributions and magnitudes in the skull of N. dicksoni were more similar to those of the living spotted-tailed quoll (Dasyurus maculatus) than to its recently extinct relative. Considering the Finite Element Analysis results and dental morphology, we predict that N. dicksoni likely occupied a broadly similar ecological niche to that of D. maculatus, and was likely capable of hunting vertebrate prey that may have exceeded its own body mass.