Affect Lipase Activity Research Articles

Dialysis with icodextrin interferes with measurement of serum alpha-amylase activity.

The glucose polymer icodextrin has gained a widespread use in peritoneal dialysis especially in patients with low ultrafiltration and high peritoneal transport properties. In patients using a once-daily exchange with icodextrin, a decreased serum amylase activity has been reported. We explored the potential underlying mechanisms of this effect. Using standard chromolytic methods, serum amylase activity was measured in blood samples from 11 patients on icodextrin treatment and from 11 patients on conventional glucose treatment. Samples were additionally supplemented with alpha-amylase and unused icodextrin dialysis fluid. Potential complex formation between icodextrin and alpha-amylase was studied by SDS-gel electrophoresis with protein silver staining and fluorophore-assisted carbohydrate staining with the AMAC (FACE) method, which provides oligosaccharide labelling. Lipase activity was measured in parallel in all samples by two standard methods. Amylase activity was reduced by 90% in serum from patients using icodextrin for the long dwell (15.9+/-10.9 U/l) vs patients using standard glucose (157.1+/-23.7 U/l; P<0.001). Addition of icodextrin to serum samples from patients using conventional glucose solutions induced a dose-dependent decrease in amylase activity. The assay results indicated a substrate competition between ET7-G7PNP and icodextrin. AMAC fluorophore staining of icodextrin and subsequent gel electrophoresis failed to demonstrate complex formation between icodextrin and alpha-amylase. Unlike the amylase findings, icodextrin did not affect lipase activity. The present findings indicate that icodextrin competitively interacts as a substrate in the amylase assay. In support of this, fluorophore-assisted oligosaccharide electrophoresis on SDS gel failed to reveal the formation of an 'amylase/icodextrin complex'. Lipase measurement should provide an alternative and unconfounded method for diagnosing pancreatitis in icodextrin patients.

DsbA and DsbC affect extracellular enzyme formation in Pseudomonas aeruginosa.

DsbA and DsbC proteins involved in the periplasmic formation of disulfide bonds in Pseudomonas aeruginosa were identified and shown to play an important role for the formation of extracellular enzymes. Mutants deficient in either dsbA or dsbC or both genes were constructed, and extracellular elastase, alkaline phosphatase, and lipase activities were determined. The dsbA mutant no longer produced these enzymes, whereas the lipase activity was doubled in the dsbC mutant. Also, extracellar lipase production was severely reduced in a P. aeruginosa dsbA mutant in which an inactive DsbA variant carrying the mutation C34S was expressed. Even when the lipase gene lipA was constitutively expressed in trans in a lipA dsbA double mutant, lipase activity in cell extracts and culture supernatants was still reduced to about 25%. Interestingly, the presence of dithiothreitol in the growth medium completely inhibited the formation of extracellular lipase whereas the addition of dithiothreitol to a cell-free culture supernatant did not affect lipase activity. We conclude that the correct formation of the disulfide bond catalyzed in vivo by DsbA is necessary to stabilize periplasmic lipase. Such a stabilization is the prerequisite for efficient secretion using the type II pathway.

Regulation of the germination of Aleppo pine (Pinus halepensis) by nitrate, ammonium, and gibberellin, and its role in post-fire forest regeneration

Aleppo pine (Pinus halepensis Mill.) regenerates after wildfires only by germination. This post-fire germination is controlled by temperature, light and the chemical characteristics of the ash-bed. The extremely high pH caused by the ash inhibits germination of Aleppo pine as well as of many other species. Here we report that ash extracts at neutral pH stimulate P. halepensis germination. The effects of ash extracts, nitrate, ammonium (in concentrations present in the ash) and GA 3 on the germination of P. halepensis seeds and on lipase activity at early germination were studied under controlled conditions. Sub-optimal concentrations of nitrate-and ammonium-stimulated germination and the activity of lipase in the seeds. It is proposed that nitrate increases seed sensitivity to GA 3 while ammonium directly affects lipase activity. The balance between the inhibition of germination by the high pH of ash and its stimulation by the nitrate and ammonium present in the ash determines the overall effect of the ash on post-fire germination of Aleppo pine. The pine seedlings appear in high density among the trees but because of the effects of the ash they appear in sparse stands under the projection of the burned pine canopies. These seedlings benefit from weak inter- and intra-specific competition as well as improved mineral nutrition and have good chances to grow into large trees that will form the regenerating forest; therefore, the enhancement of P. halepensis germination by nitrate and ammonium and its inhibition by high pH can he considered as ecophysiological adaptations to post-fire regeneration.

Heritability of Lipase Activity of Oat Caryopses

Oat (Avena sativa L.) is a potentially economically viable source of lipase, an enzyme used in foods, chemicals, and pharmaceuticals, which occurs on the surface of oat caryopses (groats). The objectives of this study were to: (i) estimate the broad‐sense heritability of the lipase activity of oat caryopses, (ii) determine the genetic and phenotypic correlations between lipase activity and other important agronomic traits, and (iii) test whether five cycles of recurrent selection for test weight caused a correlated response in lipase activity. Entries included 10 check cultivars, 95 randomly chosen S0‐derived lines from the initial cycle (C0), and 19 S0‐derived lines from C5 of a population developed by randomly mating oat cultivars and lines adapted to the midwestern USA. Entries were grown at three Iowa locations in 1996 and 1997. Broad‐sense heritability estimates for lipase activity were 0.22 on a sample basis in the population, and 0.63 on a line‐mean basis. Lipase activity had positive genetic correlations with total biomass (r = 0.31), heading date (r = 0.53), and plant height (r = 0.58), positive phenotypic correlations with heading date (r = 0.18) and plant height (r = 0.26), and negative phenotypic correlations with biomass (r = −0.13), test weight (r = −0.30), weight of 50 seeds (r = −0.18), weight of 50 groats (r = −0.40), and groat percentage (r = −0.34). The C0 and C5 populations did not differ for mean lipase activity, indicating that selection for increased test weight did not affect lipase activity. We suggest that selection for cultivars with higher lipase activity and acceptable grain quality is possible.

Sensory and Microbial Quality of Milk Processed for Extended Shelf Life by Direct Steam Injection

Heat treatments of milk between 100 and 145°C produce a new type of product with a shelf life of 15 to 30 days at 7°C, which is termed extended shelf life (ESL) milk. Little information is available on the safety and sensory qualities of this product. Extended shelf life milk is being processed commercially to expand the distribution area of fluid milk products. After arrival at market, this product still has the shelf life of a pasteurized product. In this study milk was processed by direct steam injection at temperatures between 100 and 140°C for 4 or 12 s. Holding time did not significantly affect the sensory quality of the milk. A trained taste panel found cooked flavor and other off flavors varied significantly with increasing processing temperature and storage time. There were no significant differences noted in cooked or off flavors between 132 and 140°C. Psychrotrophic Bacillus species were isolated from milk processed at and below 132°C, while no organisms were isolated from milk processed at temperatures at or above 134°C. Consumer preference panels indicated consumers preferred milk processed at 134°C for 4 s to ultrahigh-temperature (UHT) processed milk, although there was a slight preference for high-temperature short-time processed (HTST) milk compared to milk processed at 134°C for 4 s. Higher temperatures had a less destructive effect on lipase activity, while storage time did not significantly affect lipase activity.

Effects of Diet and Ketones on Rat Pancreatic Lipase in Cultured Acinar Cells

The activity, synthesis rate and mRNA level of pancreatic lipase increase with dietary fat intake. Ketones, intermediates of lipid metabolism, have been proposed to mediate this change. Therefore, we investigated their direct effect on cultured pancreatic acinar cells and examined their possible interactive effects with glucose and dietary fat. beta-Hydroxybutyrate (0.01 to 2 mmol/L) did not affect lipase activity in cells isolated from rats fed a commercial nonpurified (NP) diet and cultured in high glucose (HG, 27.8 mmol/L) or low glucose (LG, 6.9 mmol/L) medium. The effects of ketones were also examined in acinar cells isolated from rats fed purified high fat (HF, 67% of energy from fat) or low fat (LF, 11% of energy from fat) diet. Cellular lipase was significantly higher in cells from HF-fed rats at both 24 and 48 h (264% and 145% of LF values, respectively; P less than 0.0001). beta-Hydroxybutyrate significantly increased (P less than 0.04) lipase activity in LF cells at 48 h but did not affect lipase activity in HF cells. These studies suggest that ketones may be involved in the regulation of pancreatic lipase in rats fed a LF diet, but their role is complex and interactive with dietary carbohydrate and fat.

Effect of Rice Hemicelluloses on Pancreatic Lipase Activity In Vitro

ABSTRACTThe influence of rice bran water‐soluble hemicellulose on hydrolysis of fat by pancreatic lipase with and without bile salts was examined in vitro. Bile salts are required for emulsification of the oil. Three of the major salts found in human bile (sodium cholate, glycocholate, and taurocholate) were tested for emulsifying properties with and without rice hemicellulose. The lipase activity decreased with increased addition of hemicellulose to the bile salt‐enzyme reaction mixture. The results suggest that rice hemicellulose affects lipase activity indirectly by rendering the bile salts less available for emulsification of the oil and subsequent hydrolysis by the lipase.

Activation of Lipolysis. I.Distribution of Lipase Activity in Temperature Activated Milk

Temperature activation did not affect lipase activity of whole milk but altered the distribution of lipase in skim milk and cream fractions. Cooling milk to 4C caused migration of lipase activity to the cream fraction. Maximum redistribution of lipase activity was achieved by the normal temperature activation treatment of warming milk from 4C to 30C and recooling. Repeated temperature activation treatments failed to increase the amount of lipase adsorbed to the cream fraction. Storage of milk at 4C for 24h or at 22C for 2h prior to temperature activation decreased lipase activity of the cream. Warming temperature-activated milk reversed the migration of lipase activity from cream to skim milk. Relationships between lipase activities of skim milk and cream from milk before and after activation indicate that a) equilibrium between the lipase activity of skim milk and cream is temperature dependent and b) distribution of lipase in milk is determined primarily by the lipid phase.

Rapid and Sensitive Assay for Milk Lipase1,2

An improved micromethod has been developed for measuring lipase activity in milk by the pH stat technique. The silica-gel procedure measures only 16.8% of the lipase activity observed in milk by the pH stat method. The major factors contributing to this apparent low lipase activity by the silica-gel method were a) incomplete titration of the long chain free fatty acids; b) lack of proportionate response of milk lipase activity to increased concentrations of milk in the assay system; and c) variations in the pH of the lipase assay mixture during the silica-gel incubation period. Compared to the silica-gel method, the pH stat assay had greater sensitivity, accuracy, and rapidity and allowed measurement of the initial reaction velocity.During storage at 4C the lipolytic activity of fresh raw milk was constant up to 24 hr, after which it decreased. Homogenization of raw milk does not appear to affect lipase activity per se.It appears to be a substrate activating phenomenon, in that there is a direct relationship between homogenization pressure and susceptibility of milk fat to lipolysis.