Docosahexaenoic acid level of the breast milk of some Filipino women.

This study was conducted to determine the docosahexaenoic acid (DHA) level of the breast milk of 100 Filipino women as affected by diet. The subject distribution was patterned after the 1997 Family and Income Expenditure Survey of the National Statistics Office regarding the total number of families, and the total and average family income and expenditures by income class in an urban area. The subjects were asked to complete a 3-day food record and food frequency questionnaire to ascertain the nutrient content of their food intake and approximate eating habits. Hind milk was drawn manually by means of a fabricated glass breast pump and collected in polypropylene vials. The milk samples were stored in a freezer maintained at -25+/-2 degrees C until they were transported to the University of Montreal for fatty acid composition. The milk was methylated using the Lepage and Roy method. The obtained fatty acid methyl esters were analyzed by gas chromatography. Results showed that the milk samples contain an average of 188.34 microg DHA/ml milk, while %DHA of the samples is 0.65%. Regression analysis revealed that mean protein intake of the subjects was a determinant of the DHA level in the milk samples.

Kinetic analysis of the selectivity of acylcarnitine synthesis in rat mitochondria.

Mitochondrial acylcarnitine synthesis is an obligatory step in the transport of cytosolic long-chain FA into the mitochondria. It is an important control point in the partitioning of cytosolic fatty acids to synthetic pathways or to mitochondrial beta-oxidation. Mitochondrial carnitine palmitoyltransferase I (CPT I; EC 2.3.1.21) is the enzyme that catalyzes the transformation of long-chain fatty acylCoA esters to acylcarnitine. Additionally, the isoform of acylCoA synthetase (EC 6.2.1.3) found in mitochondria, which is in close proximity to CPT I on the outer membrane, may act in concert with CPT I to form acylcarnitines from cytosolic nonesterified FA (NEFA). The mitochondrial acylcarnitine synthesis pathway is exposed to multiple fatty acid substrates present simultaneously in the cell milieu, with each fatty acid present at varying pool sizes. The selectivity of this pathway for any particular fatty acid substrate under conditions of multisubstrate availability has not yet been tested experimentally. Our objective was to develop mathematical equations that make use of kinetic constants derived from single-substrate experiments to predict the selectivity of the acylcarnitine synthesis pathway under conditions in which two or more substrates are present simultaneously. In addition, the derived equations must be verifiable by experiment. Our approach was to begin with a Michaelis-Menten model that describes the initial rates of an enzyme system acting on multiple and mutually competitive substrates. From this, we derived equations expressing ratios of reaction rates and fractional turnover rates for pairs of substrates. The derived equations do not require assumptions concerning the degree of enzyme saturation. Using rat mitochondrial preparations and the NEFA substrate pairs, linolenic-oleic acids and palmitic-linoleic acids, we showed that the shape of the experimentally derived data on acylcarnitine synthesis fits the predictions of the derived model equations. We further validated the derived equations by showing that their predictions calculated from previously published kinetic constants were consistent with data from actual experiments. Thus, we are able to conclude that with respect to acylcarnitine synthesis, the fractional turnover rate of the linolenic acid pool would always be 2.9-fold faster than that of the oleate pool regardless of the pool size of either fatty acid. Similarly, the fractional turnover rate of the palmitate pool would always be 1.8-fold faster than that of the linoleate pool regardless of pool size. We extended our kinetic model to more than two mutually competitive substrates. Using previously published rate constants for eight physiologically relevant fatty acids, the derived model predicts that regardless of pool size of any of the fatty acids, the linolenate pool, whether as NEFA or as a CoA ester, would always have the highest fractional turnover rate with respect to acylcarnitine synthesis. Conversely, the stearate pool whether as NEFA or as CoA ester will have the lowest fractional turnover rate relative to all the other fatty acids.