Decrease Of NaCl Concentration Research Articles

Neuronal sensorimotor integration guiding salt concentration navigation in Caenorhabditis elegans

Animals navigate their environment by manipulating their movements and adjusting their trajectory which requires a sophisticated integration of sensory data with their current motor status. Here, we utilize the nematode Caenorhabditis elegans to explore the neural mechanisms of processing the sensory and motor information for navigation. We developed a microfluidic device which allows animals to freely move their heads while receiving temporal NaCl stimuli. We found that C. elegans regulates neck bending direction in response to temporal NaCl concentration changes in a way which is consistent with a C. elegans' navigational strategy which regulates traveling direction toward preferred NaCl concentrations. Our analysis also revealed that the activity of a neck motor neuron is significantly correlated with neck bending and activated by the decrease in NaCl concentration in a phase-dependent manner. By combining the analysis of behavioral and neural response to NaCl stimuli and optogenetic perturbation experiments, we revealed that NaCl decrease during ventral bending activates the neck motor neuron which counteracts ipsilateral bending. Simulations further suggest that this phase-dependent response of neck motor neurons can facilitate curving toward preferred salt concentrations.

Low salinity activates a virulence program in the generalist marine pathogen Photobacterium damselae subsp. damselae.

Facultative marine bacterial pathogens sense environmental signals so that the expression of virulence factors is upregulated on entry into hosts and downregulated during the free-living lifestyle in the environment. In this study, we utilized transcriptome sequencing to compare the transcriptional profiles of Photobacterium damselae subsp. damselae, a generalist pathogen that causes disease in diverse marine animals and fatal infections in humans at NaCl concentrations that mimic the free-living lifestyle or host internal milieu, respectively. We here show that NaCl concentration constitutes a major regulatory signal that shapes the transcriptome and uncover 1,808 differentially expressed genes (888 upregulated and 920 downregulated in response to low-salt conditions). Growth at 3% NaCl, a salinity that mimics the free-living lifestyle, upregulated genes involved in energy production, nitrogen metabolism, transport of compatible solutes, utilization of trehalose and fructose, and carbohydrate and amino acid metabolism with strong upregulation of the arginine deiminase system (ADS). In addition, we observed a marked increase in resistance to antibiotics at 3% NaCl. On the contrary, the low salinity conditions (1% NaCl) that mimic those encountered in the host triggered a virulence gene expression profile that maximized the production of the type 2 secretion system (T2SS)-dependent cytotoxins damselysin, phobalysin P, and a putative PirAB-like toxin, observations that were corroborated by the analysis of the secretome. Low salinity also upregulated the expression of iron-acquisition systems, efflux pumps, and other functions related to stress response and virulence. The results of this study greatly expand our knowledge of the salinity-responsive adaptations of a generalist and versatile marine pathogen. IMPORTANCE Pathogenic Vibrionaceae species experience continuous shifts of NaCl concentration in their life cycles. However, the impact of salinity changes in gene regulation has been studied in a small number of Vibrio species. In this study, we analyzed the transcriptional response of Photobacterium damselae subsp. damselae (Pdd), a generalist and facultative pathogen, to changes in salinity, and demonstrate that growth at 1% NaCl in comparison to 3% NaCl triggers a virulence program of gene expression, with a major impact in the T2SS-dependent secretome. The decrease in NaCl concentration encountered by bacteria on entry into a host is proposed to constitute a regulatory signal that upregulates a genetic program involved in host invasion and tissue damage, nutrient scavenging (notably iron), and stress responses. This study will surely inspire new research on Pdd pathobiology, as well as on other important pathogens of the family Vibrionaceae and related taxa whose salinity regulons still await investigation.

Effect of salinity on the potential cadmium phytoremediation from the polluted soil by carpobrotus rossii

Nowadays, toxic metals accumulation in soil texture due to anthropogenic activities is a major form of pollution, which can lead to worldwide concerns; however, there are many treatment methods to remove them from soil such as phytoremediation. The carpobrotus rossii, has shown great potential to tolerate high salinity and accumulate Cd from contaminated soils. The experiments, in this study, are analyzed and optimized by Central Composite Design (CCD) as method and using Response Surface Methodology (RSM) package in R software. The Cd removal by root and the whole plant followed the quadratic model and the R2 values were 94.95 and 94.81, respectively. The results showed that a decrease in NaCl concentration in Cd-containing solution can increase the phytoremediation process of Cd by carpobrotus rossii, significantly. The optimum conditions for 58% Cd removal by the whole plant, predicted through a CCD response surface methodology model were as follows: initial Cd concentration of 49 mgKg−1,NaCl concentration of 16 dSm−1, time of 17 days, and pH of 6.5. C. rossii's potential in removing 58% of Cd under the obtained optimum condition from the modelling was evaluated in real condition in the laboratory. The results revealed that around 56% of the initial added Cd concentration was removed by carpobrotus rossii. As a take home message, carpobrotus rossii can be recommended as an efficient plant to remove heavy metals especially cadmium from soil and sediments in arid area which have a salty soil.

Effect of salinity and temperature on the extraction of extracellular polymeric substances from an anaerobic sludge and fouling in submerged hollow fibre membranes

The results of the characterisation of anaerobic sludge-derived extracellular polymeric substances (EPS) under different extraction conditions and their effects on the fouling in submerged hollow fibre membranes are presented. A wide range of EPS extraction results was obtained depending on the extraction conditions. Proteins, polysaccharides, and humic substances represented 80–99% of the total organic matter extracted, with 54–60% identified as humic substances. Ultrasonication was more effective than vortex agitation, ensuring higher EPS extraction yields in a shorter contact time. The increase in temperature from 30 °C to 50 °C and the decrease in NaCl concentration favoured the EPS diffusion, but this positive temperature effect was negligible for an ultrasonic contact. Linear, quadratic, and combined effects of ultrasonication time and solvent salinity were statistically significant effects for ultrasonication-assisted EPS extraction. The highest extraction yield was achieved using ultrasonication at 30 ºC for at least 60 min with salt-free water as the solvent, and an EPS extract with 138.8 mg TOC/L was obtained. Batch ultrafiltration-backwash tests at different permeation rates allowed to determine the specific resistance to filtration of the EPS extracts, which increased from 103.8·10 12 m/kg TOC to 169.4·10 12 m/kg TOC in presence of 1.8 wt% of NaCl. Salinity also provided rigidity to the EPS gel layer, reducing the compressibility index from 0.23 to 0.03. • Ultrasonication and salt reduction favoured the diffusion of EPS. • Maximum EPS extraction required over 60 min of ultrasonication with salt-free water. • Humic substances were the predominant EPS in the side stream AnMBR sludge. • Salt increased the specific resistance and decreased the gel layer compressibility. • The retention degree increased with EPS and salt concentration.

Interaction of Midazolam with Glassy Carbon Supported Lipid Membrane in the Presence and Absence of Marker Ions

A biomimetic membrane was formed on the surface of electrochemically activated glassy carbon electrode in NaCl bath solutions. The variation of electrochemical properties of solid supported bilayer lipid membrane (s-BLM) with NaCl concentration in the bath solutions in the presence and absence of ferri/ferrocyanide marker ions was discussed using electrochemical impedance spectroscopy. The extent of pore formation on the s-BLM surface was discussed using bode phase diagram. The electrochemical impedance studies show that the partition of midazolam into the s-BLM strongly depends on Cl– ion concentration in the bath solutions. The variation of membrane capacitance with drug dose shows the ionized form of midazolam interaction with the surface of s-BLM while the neutral and ion pair forms get partitioned into the membrane. In the presence of marker ions, the membrane resistance increases with decrease in NaCl concentration in the bath solution. The cyclic voltammetric responses of marker ions for bare and drug doped s-BLMs in NaCl bath solutions were recorded and variation of redox peak currents with drug dose was discussed.

Naïve balance between structural stability and DNA-binding ability of c-Myb R2R3 under physiological ionic conditions

The minimum functional unit of c-Myb for specific DNA binding, c-Myb R2R3, fluctuates largely in solution which is critical for its DNA-binding function. The thermal stability of R2R3 increases with increasing NaCl concentrations and upon DNA binding as well. The DNA-binding affinity of R2R3 is stringently dependent on NaCl concentration, and decreases both with an increase or decrease in NaCl concentration from the physiological levels. The decreased DNA-binding affinity under low NaCl concentrations is because of the unfavorable entropy change, in contrast to the thermodynamic contribution under high NaCl concentrations. Together with the findings from thermal stability and structure analyses, the results indicate that R2R3 fluctuates more largely under low ionic strength than high ionic strength, resulting in its decreased stability and DNA-binding affinity. Under physiological conditions, R2R3 fluctuates properly to express its DNA-binding ability. The present results clearly show the naïve balance between structural stability and DNA binding.

Effect of Sodium Chloride on the Reduction of Bacillus Cereus in Shrimp Jeotgal During Refrigerated Storage

AbstractSalted shrimp Jeotgal, a favorite in Korea, is raw fermented fish containing 20–30% NaCl, which serves to inhibit its decay for a certain period. However, Bacillus cereus has been detected in commercial salted–fermented shrimp. Therefore, the goal of the present study was to examine the effect of 5–15% NaCl on the inactivation of B. cereus in various salted shrimp stored for two weeks. We determined whether NaCl could affect lactic acid bacteria and pH in salted shrimp during storage. B. cereus significantly (P < 0.05) decreased with increasing NaCl concentration and storage time at 10C. The average B. cereus count steadily and rapidly reduced before and after a 7‐day storage period, respectively. Moreover, there was no significant change in the population of lactic acid bacteria and the Hunter color (P > 0.05) during storage periods at 10C.Practical ApplicationsThis study indicates that the use of NaCl at doses of 5–15% could be an effective way to control B. cereus contamination in salted shrimp during storage at 10C. The color measurement degenerated with stepwise decrease in NaCl concentration from 7 days of storage. Therefore, we suggest that salted shrimp containing 5–15% NaCl should be consumed within 7 days.

Removal and Recovery of Acid Azo Dyes by Solvent Extraction using Cetyltrimethylammonium Chloride

Synthetic organic dyes contained in industrial effluents should be removed to avoid health hazards and destruction of the ecosystem. In this study, the extraction of acidic azo dyes to cetyltrimethylammonium chloride (CTAC)/1-hexanol/isooctane solution was investigated. It was found that acidic dyes were extracted to the organic solution by electrostatic interaction between sulfo group of dyes and CTAC. The extraction ratio of dyes increased with an increase in CTAC concentration and with a decrease in NaCl concentration, and generally was not affected by dye concentration and pH. The extraction of acidic dyes by CTAC was explained by ion-exchange mechanism and the extraction equilibrium constants were estimated from the experimental data. AR13 and AR27 extracted to CTAC organic solution were recovered into stripping solution of high NaCl concentration, and AO52 was recovered into that of low pH. There was no deterioration of the forward and backward extraction behavior by the reused CTAC organic solution.

Thrombin Inhibition by Serpins Disrupts Exosite II

Thrombin uses three principal sites, the active site, exosite I, and exosite II, for recognition of its many cofactors and substrates. It is synthesized in the zymogen form, prothrombin, and its activation at the end of the blood coagulation cascade results in the formation of the active site and exosite I and the exposure of exosite II. The physiological inhibitors of thrombin are all serpins, whose mechanism involves significant conformational change in both serpin and protease. It has been shown that the formation of the thrombin-serpin final complex disorders the active site and exosite I of thrombin, but exosite II is thought to remain functional. It has also been hypothesized that thrombin contains a receptor-binding site that is exposed upon final complex formation. The position of this cryptic site may depend on the regions of thrombin unfolded by serpin complexation. Here we investigate the conformation of thrombin in its final complex with serpins and find that in addition to exosite I, exosite II is also disordered, as reflected by a loss of affinity for the γ'-peptide of fibrinogen and for heparin and by susceptibility to limited proteolysis. This disordering of exosite II occurs for all tested natural thrombin-inhibiting serpins. Our data suggest a novel framework for understanding serpin function, especially with respect to thrombin inhibition, where serpins functionally "rezymogenize" proteases to ensure complete loss of activity and cofactor binding.

Functional role of aquaglyceroporin 7 expression in the pancreatic beta‐cell line BRIN‐BD11

Both mouse and rat pancreatic islet beta-cells were recently found to express aquaglyceroporin 7 (AQP7). In the present study, the expression and role of AQP7 in the function of BRIN-BD11 cells were investigated. AQP7 mRNA and protein were detected by RT-PCR and Western blot analysis, respectively. In an isoosmolar medium, the net uptake of [2-(3)H]glycerol displayed an exponential time course reaching an equilibrium plateau value close to its extracellular concentration. Within 2 min of incubation in a hypotonic medium (caused by a 50 mM decrease in NaCl concentration), the [2-(3)H]glycerol uptake averaged 143.2 +/- 3.8% (n = 24; P < 0.001) of its control value in isotonic medium, declining thereafter consistently with previously demonstrated volume regulatory decrease. When isoosmolarity was restored by the addition of 100 mM urea to the hypotonic medium, [2-(3)H]glycerol uptake remained higher (112.1 +/- 2.8%, n = 24; P < 0.001) than its matched control under isotonic conditions, indicating rapid entry of urea and water. Insulin release by BRIN-BD11 cells was 3 times higher in hypotonic than in isotonic medium. When glycerol (100 mM) or urea (100 mM) were incorporated in the hypotonic medium, the insulin release remained significantly higher than that found in the control isotonic medium, averaging respectively 120.2 +/- 4.2 and 107.0 +/- 3.8% of the paired value recorded in the hypotonic medium. These findings document the rapid entry of glycerol and urea in BRIN-BD11 cells, likely mediated by AQP7.

Improved monospermic fertilization and subsequent blastocyst formation of bovine oocytes fertilized in vitro in a medium containing NaCl of decreased concentration.

The objective of this study was to evaluate whether changes in NaCl concentration in a fertilization medium could improve normal fertilization and preimplantation development of bovine oocytes. In vitro matured bovine oocytes were inseminated with frozen-thawed semen for 18 hr in a Tyrode's medium with albumin, lactate and pyruvate (TALP), to which 114 (TALP-114), 96 (TALP-96) or 78 (TALP-78) mM NaCl was added. Presumptive zygotes were cultured for 192 hr in a modified TALP containing 90 mM NaCl, 1.5 mM glucose, 0.3% (w/v) BSA, minimal essential medium (MEM) essential and nonessential amino acids, and insulin-transferrin-selenium complex. Lower polyspermy rate was obtained by the insemination in TALP-96 (7.8 +/- 2.3%) than by the insemination in TALP-114 (25.6 +/- 1.4%), without decrease in male pronucleus (MPN) formation. Fertilization in TALP-78 also yielded decreased polyspermic fertilization (3.8 +/- 1.5%), but significant decrease in MPN formation was found (63.1 +/- 3.1%). In preimplantation development, more blastocysts developed from oocytes inseminated in TALP-96 (24.1 +/- 1.7%) than from oocytes inseminated in TALP-114 (16.8 +/- 1.4%). TALP-78, however, did not improve preimplantation development beyond the 8-cell stage compared with TALP-114. Mean cell number of blastocyst was higher when oocytes were fertilized in TALP-96 (137.0 +/- 4.5) than in TALP-114 (123.1 +/- 5.1) and in TALP-78 (102.3 +/- 4.5). These results demonstrate that insemination of bovine oocytes in a TALP with decreased NaCl concentration (96 mM) improves blastocyst formation and embryo viability. Decrease in NaCl concentration below 96 mM, however, may delay or inhibit MPN formation, and inhibits subsequent development in vitro.

202 高濃度 NaCl 水溶液による細胞損傷に及ぼす温度の影響

Exposure to hypertonic solution during freezing is believed to be one of the major causes of the post-thaw cellular injury after freezing at low cooling rates. We have characterized the post-hypertonic survival at 23℃ as a function of hypertonic NaCl concentration, the time of exposure, and the rate of increase or decrease in NaCl concentration by using a newly developed perfusion technique. In the present report the same experiments are carried out at 0℃ and compared with the previous result at 23℃. The cell membrane permeability to water is also measured to explain the obtained result.

Double critical behavior and micellar size effect in the multicomponent surfactant solution

Multicomponent surfactant system, sodium dodecyl sulfate and butanol in an aqueous NaCl solution, which exhibits a closed-loop type reentrant phase separation, was investigated by light scattering experiments focusing on the double critical behaviors and the finite micellar size effect on the dynamic critical behavior. The loop size decreased with the decrease of NaCl concentration, and the double critical point appeared. Approaching the double critical point, the critical exponents ν for the long-range correlation length ξ and γ for the isothermal osmotic compressibility χT determined by use of the spinodal divergency theory showed a crossover behavior from Fisher’s renormalized Ising model values to the doubling of them. ξ and χT formed master curves as a function of εUL=|(TU−T)(TL−T)|/TUTL, and had the effective critical exponents ν=0.73 and γ=1.41 ascertaining the validity of Fisher’s renormalized Ising model. Here, TU and TL are the upper and lower critical solution temperatures, respectively. Dynamic critical behaviors were well explained in a unified manner over the hydrodynamic and critical regions by the modified dynamical droplet model taking the finite micellar size into account, which assumes that the local fluctuations activated thermally behave as the physical clusters with a fractal dimension of df=2.49 and a polydispersity exponent of τ=2.21. The evaluated monomer unit sizes are in good agreement with the micellar sizes obtained independently.

Current Distribution and Electrochemical Environment in a Cathodically Protected Crevice

Abstract Current and potential distributions inside the crevice of a simulated disbonded coating with a holiday during cathodic protection (CP) of steel were measured experimentally in 0.001 M to 0.6 M sodium chloride (NaCl) solutions covering a range of conductivity from 0.012 Ω−1 m−1 to 5.1 Ω−1 m−1. The circular crevice was 95 mm in radius, 0.8 mm in thickness, and open to the test solution through a holiday of 5 mm in radius on the center of the coating. Microelectrodes mounted on the steel surface were used to determine the local current densities inside the crevice. Change in the concentration of dissolved oxygen inside the crevice was monitored with a micro-oxygen electrode. Current distribution was extremely nonuniform. Depending upon NaCl concentrations, the local current density on steel exhibited a 100-fold decrease from that at the holiday opening within 20 mm to 40 mm into the crevice. Current and potential distribution curves became less uniform with a decrease in NaCl concentration and solut...

Mechanisms of cell volume regulation in the proximal segment of the Malpighian tubule of Rhodnius neglectus.

The cell volume regulation of the lower segment cells of the Malpighian tubule of Rhodnius neglectus in anisosmotic media was evaluated by using video-optic techniques. When the medium osmolality was increased with addition of 100 mM mannitol the cells shrank to a minimum of 16.84 +/- 2.62% and subsequently swelled towards their initial volume undergoing a typical regulatory volume increase (RVI). Replacement of either K+ or Cl- or HCO(3-) by Na+, gluconate and phosphate, respectively, abolished the RVI response. Furthermore, the substitution of Na+ by tetramethylammonium (TMA+) in isosmotic conditions led to cellular swelling and death. Addition of either amiloride 10(-4) M, anthracene-9-COOH 5 x 10(-4) M, furosemide 5 x 10(-4) M or ethacrynic acid 5 x 10(-5) M, also abolished RVI. On the other hand, addition of either Ba2+ 10(-3) M, SITS 5 x 10(-4) M, ouabain 10(-3) M or vanadate 10(-3) M, did not change the RVI response. When the tubules were incubated in hyperosmotic media with EGTA 2 mM or verapamil 10(-6) M, the RVI response was abolished. In contrast, a decrease of NaCl concentration from 129 to 79 mM induced a cell swelling to a maximum of 33.11 +/- 1.73%, but the cells maintained swollen, only partially regulating their volume. These results show that the proximal cells of Malpighian tubule of R. neglectus are able to regulate their volume in hyperosmotic but only partially regulating in hyposmotic solutions. The mechanisms in RVI involve Na+, K+, Cl-, Ca2+ and HCO(3-) transport pathways and a ouabain-insensitive ATPase stimulated by Na+.

Characterization of the macula densa stimulus for renin secretion

These studies utilize the isolated perfused rabbit juxtaglomerular apparatus (JGA) to study the macula densa signal for renin secretion in the absence of the confounding influences of intravascular pressure and renal nerve activity. In the first experimental series, JGAs were perfused alternately with high- and low-NaCl solutions to determine the reversibility of the renin response to changes in NaCl concentration. Compared with high-NaCl controls, perfusion with a low-NaCl solution resulted in a fivefold increase in renin secretion rate (RSR) [2.1-10.0 nano-Goldblatt hog units (nGU)/min], and this response was largely reversible. When the solutions were presented in the reverse order, a similar inhibition by high NaCl was observed. In the second series, JGAs were perfused with high-, medium-, and low-NaCl solutions to determine the sensitive range of the renin response to NaCl concentration changes. The full renin response (3.2-16.6 nGU/min), similar in magnitude to that seen in series 1, was found to occur between 80 and 24 mM for Na+ and 61 and 7 mM for Cl-. In the third series, the NaCl concentration and flow rate of the perfusate were altered independently to separate the effects of flow rate, NaCl delivery, and NaCl concentration on RSR. Although a decrease in perfusate flow rate slightly increased RSR (3.4-8.1 nGU/min), a comparable decrease in NaCl concentration resulted in a much higher RSR (26.3 nGU/min). We conclude that in this preparation 1) RSR responds equally to both increases and decreases in macula densa NaCl concentration, and these changes are rapid and largely reversible, 2) the full renin response occurs within the concentration range normally occurring at the macula densa, i.e., below 80 mM Na+ and 61 mM Cl-, and 3) RSR responds with a larger change to alterations in NaCl concentration than in NaCl delivery or fluid flow rate.

Regulation by batrachotoxin, veratridine, and monensin of basal and carbachol-induced phosphoinositide hydrolysis in neurohybrid NCB-20 cells

Batrachotoxin (BTX), veratridine and monensin induced a time- and dose-dependent increase of [3H]-inositol monophosphate (3H-IP1) accumulation in the presence of lithium in prelabeled neurohybrid NCB-20 cells. A decrease of NaCl concentration to less than 30 mM markedly increased basal 3H-IP1 accumulation; however, the percentage of stimulation induced by these three agents remained unchanged even in the complete absence of sodium. The stimulation of phosphoinositide hydrolysis induced by these agents was detected in the absence of lithium but was largely prevented in the calcium-free medium. Tetradotoxin (TTX) blocked effects of BTX and veratridine (IC50 approximately 20nM), but not that stimulated by monensin. Thus, calcium-dependent activation of phospholipase C by these agents did not involve the entry of sodium or lithium. BTX and monensin also induced greater than additive effects on carbachol-induced 3H-IP1 accumulation. These effects were also TTX-sensitive and involved an increase in the Vmax and a decrease in the EC50 for carbachol. Veratridine provoked strikingly different effects on carbachol-dependent phosphoinositide turnover, depending on the passage number of the cells.

Métabolisme des hydrocarbures chez une bactérie marine

The marine bacterium L.16.1 (Alcaligenes sp.) grows preferentially on alkanes (C10 to C18) with a very high growth yield (98 per cent); optimal growth depends strictly on the presence of a well-defined NaCl concentration (100 mM). Our strain is constitutive for the enzymatic systems responsible for the oxidation of alkanes to fatty acids, i.e. NADH-dependent hydroxylase, alcohol and aldehyde dehydrogenases, the latter of which located at the cytoplasmic membrane level. The aerobic oxidation of primary alcohols by particulate extracts prepared in the presence of 400 mM NaCl is NAD+-dependent (Km = 0.082 mM, Vmax = 238 with decanol). With extracts prepared in the absence of NaCl, Vmax undergoes a very strong decrease. On the contrary , the NAD+ (P)+-dependent oxidation of aldehydes is carried out anaerobically by the same extracts irrespective of the presence or the absence of added Na+ in the solutions used for the preparation of these extracts. A possible explanation for our results could be that Na+ acts on the enzymatic systems for which the maintenance of the membrane integrity is essential. This interpretation is consistent with the slowing down of the growth speed accompanying the decrease of NaCl concentration in the growth medium. With regard to alcohol and aldehyde-dehydrogenases, it is noteworthy that these enzymes behave like similar enzymatic activities induced by alkanes in other microorganisms.

Effects of external osmolality on polyamine metabolism in HeLa cells

The polyamine content of Escherichia coli is inversely related to the osmolality of the growth medium. The experiments described here demonstrate that a similar phenomenon occurs in mammalian cells. When grown in media of low NaCl concentration, HeLa cells and human fibroblasts were found to contain high levels of putrescine, spermidine, and spermine. The putrescine content of HeLa cells was a function of the osmolality of the medium, as shown by growing cells in media containing mannitol or additional glucose. External osmolality per se had no effect on the contents of spermidine and spermine. For all media, the total cellular polyamine content could be correlated with the activity of ornithine decarboxylase, the first enzyme in polyamine biosynthesis. Different levels of enzyme activity appear to result solely from variations in the rate of enzyme degradation. A sudden increase in NaCl concentration produced rapid loss of ornithine decarboxylase activity and a gradual loss of putrescine and spermidine. A sudden decrease in NaCl concentration led to rapid and substantial increases in ornithine decarboxylase activity and putrescine.

Proteolysis of β-casein in Cheddar Cheese

Summaryβ-Casein is highly resistant to proteolysis in Cheddar cheese. A decrease in NaCl concentration reduced its resistance, but even in the absence of salt the amount of proteolysis of β-casein was slight. Proteolysis in Cheddar cheese increased when the moisture levels were raised by adding water. The relative susceptibility of β-casein to proteolysis by rennin was reduced considerably when the concentration of a sodium caseinate solution was raised from 10 to 20%. Sequestering the Ca2+by means of EDTA had no significant effect on proteolysis of β-casein. It would appear that the resistance of β-casein to proteolysis is due to the substrate rather than the enzyme and it is suggested that the reduced relative susceptibility to proteolysis is due to some concentration-dependent physical change in the casein molecule which renders the β-casein inaccessible. The salt concentration would also appear to influence this change.Cheddar-cheese flavour is largely independent of rennet concentration and it is possible to manufacture cheese of satisfactory quality using half-normal rennet levels.