A colorimetric determination of fatty acids as a new assay of lipases in reverse micelles

A new simple spectrophotometric method is described for the determination of the free fatty acid content in triglyceride oils or other lipophilic samples. The method utilizes phenol red as fatty acid indicator, which is solubilized phenol red as fatty acid indicator, which is solubilized in reverse micelles formed by AOT [sodiumbis(2-ethylhexyl) sulfosuccinate] in isooctane. Fatty acid determinations in vegetable oils can be carried out rapidly with oil samples of less than 100 mg. The acid value of three different oils tested agreed quite well with the acid value obtained for the same samples with another colorimetric determination using cupric acetate. The method can be extended to a continuous determination of fatty acids which are released during the initial stage of a lipase catalyzed hydrolysis of triglyceride substrates in reverse micelles. This new sensitive lipase assay has been applied for a lipase ofPseudomonas bacteria with lipase concentrations as low as 0.1 μg/ml. Using trioctanoylglycerol as substrate in 50 mM AOT/isooctane with w_o=[H₂O]/[AOT]=11.1 (pH 9.0), the apparent overall Michaelis-Menten constant (K_m′app,ov) is 27 mM and the turnover number (k_cat) 44 sec⁻¹.     

Optimizing storage performance in public cloud platforms

Cloud computing is an elastic computing model where users can lease computing and storage resources on demand from a remote infrastructure.It is gaining popularity due to its low cost,high reliability,...     

A model for studying LCAT reaction: In vitro cholesterol esterification in pig ovarian follicular fluid

Phosphatidylcholine acyltransferase (lecithin:cholesterol acyltransferase or LCAT; EC 2.3.1.43) activity was found to be present in pig ovarian follicular fluid (POFF), in addition to pig serum (PS). The cholesterol esterification rate in both POFF and PS is linear with incubation time up to 2 hr. The mean absolute rate of POFF-cholesterol esterification was 8.1±0.4 nmoles per ml per hr approximately one-fourth of that in PS. However, the fractional rate (percent of labeled cholesterol esterified per hr) of POFF-cholesterol esterification was similar to that observed in PS. There was little variation of absolute rate of cholesterol esterification in the fluid obtained from different sizes of follicles. Fatty acid or triacylglycerol did not participate in the reaction of cholesterol esterification in POFF. No appreciable change in enzymatic activity was found from storing POFF at 4 C for periods of time up to 24 hr or at −70 C up to 2 months, but activity was lost thereafter. On the other hand, PS showed a much longer period of stability (5 days at 4 C and 9 months at −70 C). A discrepancy between the fatty acid composition of cholesteryl esters formed by the LCAT reaction and the fatty acid composition at the C-2 position of phosphatidylcholine led us to propose a two-step mechanism for the LCAT reaction. It is concluded that the LCAT of POFF, as well as that of plasma, is specific for individual fatty acids rather than for the fatty acid composition of phosphatidylcholine. The fatty acid concentration of lysophosphatidylcholine decreased during prolonged incubation times (6 to 21 hr) suggesting that the increased lysophosphatidylcholine formed as a product of the LCAT reaction may be reused as substrate for the LCAT reaction or for hydrolysis by lysophosphatidylcholine hydrolase. Presented at the AOCS Meeting, New York, May 1977.     

Coordinate descent with arbitrary sampling I: algorithms and complexity†

We study the problem of minimizing the sum of a smooth convex function and a convex block-separable regularizer and propose a new randomized coordinate descent method, which we call ALPHA. Our method at every iteration updates a random subset of coordinates, following an arbitrary distribution. No coordinate descent methods capable to handle an arbitrary sampling have been studied in the literature before for this problem. ALPHA is a very flexible algorithm: in special cases, it reduces to deterministic and randomized methods such as gradient descent, coordinate descent, parallel coordinate descent and distributed coordinate descent—both in nonaccelerated and accelerated variants. The variants with arbitrary (or importance) sampling are new. We provide a complexity analysis of ALPHA, from which we deduce as a direct corollary complexity bounds for its many variants, all matching or improving best known bounds.