Catherine Verret

Isolation and identification of a μ-calpain-protein kinase Cα complex in skeletal muscle

A μ‐calpain‐PKC complex was isolated from rabbit skeletal muscle by ultracentrifugation and by anion‐exchange chromatography. The PKC associated to μ‐calpain was stimulated by calcium, phosphatidylserine and diacylglycerol, and corresponds to a conventional PKC (cPKC). This complex presents an apparent molecular mass close to 190 kDa and is composed of one μ‐calpain molecule and of one cPKC molecule. Using monoclonal antibodies specific for the different cPKC isoforms, the isoenzyme associated to μ‐calpain was identified as cPKCα. Immunofluorescence staining reveals a co‐localization of μ‐calpain and cPKCα on the muscle fibre plasma membranes.

Changes in Volatile Aromatic Compounds of Strawberry Puree Treated by High-pressure During Storage

The changes in volatile flavor components and lipoxygenase and peroxidase enzymatic activity of Cilady strawberry puree during high pressure processing (400 MPa/20 °C/20 min) and storage at 4 °C were evaluated. High pressure processing maintains the original aromatic distribution, but after thirty days of storage an increase in some volatile compounds was observed. After high pressure treatment and storage, a residual lipoxygenase activity was observed, which could explain some slight changes of volatile compounds. On the other hand, the peroxidase was clearly inactivated by high pressure treatment.

Calpain-PKC Inter-Relations in Mouse Hippocampus: A Biochemical Approach

In previous studies, we isolated and identified a μ-calpain/PKCα complex from rabbit skeletal muscle. Here, we have used specific purification procedures in order to study the interactions between μ-calpain and PKC in mouse hippocampus, a brain structure implicated in memory processes. We observed that μ-calpain and conventional PKCs (α, βII and γ) are co-eluted after anion exchange chromatography. In contrast to our previous results obtained on skeletal muscle, μ-calpain and PKC isoenzymes were dissociated after gel filtration chromatography. Furthermore, μ-calpain induced the proteolytic conversion of PKCα, βII, and γ into PKMα, βII, and γ with a preferential hydrolysis of PKCγ, a specific isoenzyme of the nervous system. Although the μ-calpain/PKC interactions in the hippocampus are quite different from skeletal muscle, our results however, point out the functional importance of these inter-relations. Moreover, as PKCγ has been involved in the biochemical events underlying learning and memory, the preferential relationship between μ-calpain and PKCγ promotes the importance of the role that μ-calpain could play in the cellular mechanisms of memory formation.

Degradation of protein kinase Mα by μ-calpain in a μ-calpain-protein kinase Cα complex

Abstract In previous studies, we isolated and identified a μ-calpain-PKCα complex from rabbit skeletal muscle. At the same time we pointed out that an association between μ-calpain and PKCα could occur at the level of the plasma membrane of muscle cells, and that PKCα could thus be considered as a potential μ-calpain substrate. In the present study, using the μ-calpain-PKCα complex as a model, we report that μ-calpain is activated in the combined presence of physiological calcium concentrations (less than 1 μM) and phosphatidylserine. Furthermore our data also show that: (1) there exists a correlation between the appearance of autolyzed μ-calpain forms and PKCα hydrolysis which leads to the formation of PKMα; (2) in certain experimental conditions, autolyzed μ-calpain forms are able to hydrolyze PKMα independently of the presence of diacylglycerol.

Effects of high pressure on anhydrous milk fat crystallization in emulsion

Anhydrous milk fat crystallization was compared either in bulk phase or in oil in water emulsion by studying melting curves obtained by calorimetry measurements. Emulsions were submitted to a high pressure (HP) treatment (200 MPa/10 min). An aging period of 72 h was required to obtain the highest amount of crystallized fat at 4 °C. Emulsification promoted the crystallization of low melting point (LMP) triglycerides. The effect of HP on anhydrous milk fat crystallization depended on the aging time. For short aging periods (30 min and 1 h), HP treatment favored the crystallization of LMP triglycerides, thus amplifying the effect of emulsification compared with the crystallization in bulk phase. However, for a long aging time, i.e. 48 h, the amounts of crystallized matter in emulsion with or without HP treatment were comparable. This result was interpreted in terms of a different polymorphic form crystallizing under HP.

Effect of high pressure treatment on the characteristics of a model emulsion

The aim of this study was to investigate the use of HP (high pressure) technology as a possible alternative method for decontamination of non-food medium. HP (500 MPa) did not modify significantly the physicochemical characteristics of a model non-food emulsion. A 10 min HP treatment inactivated totally Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger and Candida albicans even if all the five microorganisms were inoculated together, regardless of the initial load. No recovery was observed until six months of storage at 25°C.

High pressure inactivation of Pseudomonas in black truffle – comparison with Pseudomonas fluorescens in tryptone soya broth

Pseudomonas is one of the most common genera in black Perigord truffle. Its inactivation by high pressure (100–500 MPa/10 min) applied on truffles at sub-zero or low temperatures was studied and compared with those of Pseudomonas fluorescens in tryptone soya broth. Pressurization of truffles at 300 MPa/4 °C reduced the bacterial count of Pseudomonas by 5.3 log cycles. Higher pressures of 400 or 500 MPa, at 4 °C or 20 °C, allowed us to slightly increase the level of destruction to the value of ca. 6.5 log cycles but did not permit us to completely inactivate Pseudomonas. The results showed a residual charge of about 10 CFU/g. Pressure-shift freezing of truffles, which consists in applying a pressure of 200 MPa/−18 °C for 10 min and then quickly releasing this pressure to induce freezing, reduced the population of Pseudomonas by 3.3 log cycles. The level of inactivation was higher than those obtained with conventional freezing. Endogenous Pseudomonas in truffle was shown to be more resistant to high pressure treatments than P. fluorescens used for inoculation of broths.

The effect of high hydrostatic pressure on black truffle (tuber melanosporum) flavour compounds

The effects of high hydrostatic pressure (HHP), at 4°C or -18°C, on black truffle flavour compounds, alteration enzymes (lipoxigenase (LOX), peroxidase (POD) and polyphenoloxidase (PPO)) and microbiological qualities were evaluated. The choosen analytes for this study are six alcohols, three aldehydes, one ketone and on sulfur component. The highest flavour stability was observed when samples were pressurized at 300 MPa / 4°C / 10 min. All the treatments induced a drastic decrease of LOX activity and a slight decrease of POD activity. On the other hand, the PPO was not inactivated by pressurization at sub-zero (200 MPa / -18°C / 10 min) and was strongly increased after the 300 MPa / 4°C / 10 min treatment. Pressurization at 300 and 550 MPa lead to an almost complete Pseudomonas fluorescens reduction (6 and 6.5 log destruction, respectively) whereas pressurization at -18°C (200MPa) allowed to obtain only 3 log reduction.

Effect of High-pressure Treatment on Polyphenoloxidase Activity of the Agaricus Bisporus Mushroom

High pressure treatments (100-500 Mpa/4 °C/10 min) were carried out on freshly sliced mushrooms ( Agaricus bisporus ) and on liquid extract. Pressure above 200 MPa led to respiratory activity loss, significant enzymatic browning and polyphenoloxidase (PPO) activation in treated mushrooms. Increasing pressure from 200 to 500 MPa enhanced the PPO activation (in whole tissue and in liquid extract). Stabilization of mushroom by high-pressure (HP) alone cannot be considered. A combination of HP with thermal or chemical treatments is found necessary.

Stabilisation of Strawberry Puree Treated by High Pressure During Storage

The pressure treatment (400 MPa / 20°C / 20 min) was carried out on fresh Cilady strawberry puree. High pressure processing maintained the original aromatic distribution and after thirty days of storage, some volatile compounds were slightly modified. In similar conditions, a residual lipoxygenase activity was observed which increased during storage. On the other hand, the peroxidase activity and bacterial growth were clearly inactivated by high pressure treatment and after thirty days of storage at 4°C.