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R G Jensen

Publications and source records attributed to R G Jensen.

At least 37 records · Page 2Linked to original sources
PubMed1994

Fatty acid and positional selectivities of gastric lipase from premature human infants: in vitro studies.

Gastric lipase activity in aspirates from premature human infants was tested for fatty acid and positional selectivity using racemic diacid triacylglycerols (TG) as substrates. The resulting free fatty acids and monoacylglycerols (MG) were recovered and analyzed. Octanoic acid (8:0) and decanoic acid (10:0) were hydrolyzed with a preference of 61.5:1 and 2.4:1 compared to palmitic acid (16:0) from rac-16:0-8:0-8:0 and rac-16:0-10:0-10:0, respectively. The ratio of lauric acid (12:0) to oleic acid (18:1) hydrolyzed from rac-18:1-12:0-12:0 was 13:1. Myristic acid (14:0), 18:1 and linoleic acid (18:2) were released at similar rates. These data and the composition of the MG suggest that, in vitro, the lipase is selective for shorter chain fatty acids and for fatty acids on the primary positions of the TG backbone.

Caprylates↗
PubMed1994

Total lipid and fatty acid composition of milk from women with and without insulin-dependent diabetes mellitus.

Milk lipid and fatty acids were measured from women with insulin-dependent diabetes mellitus (IDDM), a comparison group of women without diabetes, and reference women. Milk samples were collected 80 min after breakfast at 2, 3, 7, 14, 42, and 84 d postpartum (pp). Total lipid and medium-chain fatty acids (MCFAs) in the group with IDDM were similar to or greater than those of control and reference groups at all times and were within normal, reported ranges. Milk long-chain polyunsaturated fatty acids (LC-PUFAs) were lower in women with IDDM from 14 to 84 d pp. Lower milk LC-PUFAs may be a result of altered fatty acid metabolism in women with IDDM.

Adult↗
PubMed1993

Anion exchange separation and pulsed amperometric detection of inositols from flower petals.

A rapid and specific method for the separation of cyclic sugar alcohols by anion exchange HPLC and subsequent detection by pulsed amperometry is presented. The cyclitols include the inositols and O-methyl inositols. Although examples use plant extracts the method has general application and is suitable for detecting as little as 10 pmol of substance. Carbohydrates are weak acids with pKa values typically above 12. While separation of most monosaccharides on high-performance anion exchange columns in aqueous NaOH is adequate, the ionization of inositols and O-methyl inositols is weak and their separation is poor. Use of a high-capacity anion exchange column separated the inositols well but the more ionized sugars were tightly retained. Automatic switching of the inositol fraction eluting from the lower-capacity column onto the high-capacity column with subsequent detection by pulsed amperometry gave specific and rapid separations of the inositols with a turnaround time of 16 min. As an example of application, we chose the separation and identification of cyclic and acyclic sugar alcohols in flower petals from a variety of plants. There was an apparent correlation between the postharvest longevity of flowers and the content of inositols, particularly D-pinitol.

Chromatography, High Pressure Liquid↗
PubMed1993

Delayed lactogenesis in women with insulin-dependent diabetes mellitus.

Breast milk lactose, total nitrogen, conductivity, osmolality, and intake by infants of 33 women with insulin-dependent diabetes mellitus (IDDM), 33 control women without diabetes, and 11 reference women were determined in a 3-mo study of lactation. Milk of women with IDDM had significantly lower lactose and higher total nitrogen (2-3 d postpartum), and their infants had significantly less milk intake (7-14 d postpartum) than did control or reference women. Total nitrogen was negatively correlated with milk lactose for women with IDDM at all times and for control women through day 14 postpartum. The data indicate delayed lactogenesis for women with IDDM, which was more likely to occur with poor metabolic control. Differences in milk composition of women with IDDM do not preclude them from breast-feeding their infants.

Diabetes Mellitus, Type 1↗
PubMed1992

Expression of a bacterial mtlD gene in transgenic tobacco leads to production and accumulation of mannitol.

A bacterial gene encoding mannitol-1-phosphate dehydrogenase, mtlD, was engineered for expression in higher plants. Gene constructions were stably incorporated into tobacco plants. The mtlD gene was expressed and translated into a functional enzyme in tobacco, resulting in the synthesis and accumulation of mannitol, which was identified by NMR and mass spectroscopy. Mannitol concentrations exceeded 6 mumol/g (fresh weight) in the leaves and in the roots of some transformants, whereas this sugar alcohol was not detected in these organs of wild-type tobacco plants or of untransformed tobacco plants that underwent the same regeneration scheme. These experiments demonstrate that branch-points in plant carbohydrate metabolism can be generated by which novel gene products can utilize endogenous substrates to divert metabolic energy into novel compounds. Additionally, the system described here allows for physiological studies in which the responses of wild-type and transgenic tobacco to various environmental stimuli can be compared directly. Such studies will facilitate our understanding of the roles of sugar alcohols (e.g., in stress tolerance) in higher plants.

Escherichia coli↗
PubMed1992

Effect of fish oil on the fatty acid composition of human milk and maternal and infant erythrocytes.

To examine the effect of fish oil supplementation on the fatty acid (FA) composition of human milk and maternal and infant erythrocytes, five lactating women were supplemented with 6 g of fish oil daily for 21 d. Usual maternal diets contained 1,147 mg of total n-3 FA, with 120 mg from very long-chain (> C18) n-3 FA. Supplementation increased dietary levels to 3,092 mg of total n-3 FA and 2,006 mg of very long-chain n-3 FA. Milk samples were collected daily, prior to fish oil ingestion, and at 4-h intervals on days 1, 7, 14 and 21. Milk n-3 FA content increased within 8 h and reached steady state levels within one week. The n-6 fatty acid content decreased. Erythrocyte eicosapentaenoic acid content increased from 0.24% to 1.4% (P < 0.01) in mothers and from 0.11% to 0.70% (P < 0.05) in infants. Docosapentaenoic acid increased from 1.4% to 2.2% (P < 0.05) in mothers and from 0.30% to 0.78% (P < 0.01) in infants. There was no significant change in docosahexaenoic acid or n-6 fatty acid content. Maternal platelet aggregation responses were variable. No differences in milk or plasma tocopherol levels were noted.

Dietary Fats, Unsaturated↗
PubMed1992

Effect of dietary intake of n-6 and n-3 fatty acids on the fatty acid composition of human milk in North America.

To determine the effect of maternal dietary n-6 and n-3 polyunsaturated fatty acids (PUFA) on the amounts of these fatty acids in human milk, two criteria must be met. These are assessment of the maternal diet and accurate analysis of the milk fatty acids. This type of analysis requires gas-liquid chromatography with capillary columns to resolve important n-6 and n-3 C20 and C22 fatty acid. This type of analytic equipment has only recently become available; thus the amount of complete data on human milk fatty acids is limited. To assess actual fatty acid intakes by the infant, the fat content and volume of milk received by the infant must be known. Alterations in maternal dietary intake of PUFA cause similar changes in milk PUFA. Several investigators have shown that maternal supplementation with fish oils increases the amounts of 20:5n-3 and 22:6n-3 in milk and maternal and infant erythrocyte lipids. A new mathematic index for assessment of essential fatty acid status, the mean melting point of plasma phospholipid fatty acids, has been proposed. We found in some mother-infant pairs that maternal supplementation with fish oil lowered the mean melting points of erythrocyte lipids to levels seen in nonpregnant women.

Diet↗
PubMed1992

Simple Determination of the CO(2)/O(2) Specificity of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase by the Specific Radioactivity of [C]Glycerate 3-Phosphate.

A new method is presented for measurement of the CO(2)/O(2) specificity factor of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The [(14)C]3-phosphoglycerate (PGA) from the Rubisco carboxylase reaction and its dilution by the Rubisco oxygenase reaction was monitored by directly measuring the specific radioactivity of PGA. (14)CO(2) fixation with Rubisco occurred under two reaction conditions: carboxylase with oxygenase with 40 micromolar CO(2) in O(2)-saturated water and carboxylase only with 160 micromolar CO(2) under N(2). Detection of the specific radioactivity used the amount of PGA as obtained from the peak area, which was determined by pulsed amperometry following separation by high-performance anion exchange chromatography and the radioactive counts of the [(14)C]PGA in the same peak. The specificity factor of Rubisco from spinach (Spinacia oleracea L.) (93 +/- 4), from the green alga Chlamydomonas reinhardtii (66 +/- 1), and from the photosynthetic bacterium Rhodospirillum rubrum (13) were comparable with the published values measured by different methods.

Journal Article↗
PubMed1992

Lipids in human milk and infant formulas.

About 50 metabolically important fatty acids can be identified in human milk. The extent of absorption of milk fatty acids varies considerably from infant to infant, particularly in pre-term infants, and requires more study. Human milk provides sufficient vitamins A and E for the term infant, but supplementation with vitamins D and K may be necessary. More research is needed on the amounts of the fat-soluble vitamins in human milk, the efficiency of transfer from mother to infant, the reasons for variation in different women, and the consequences to breast-fed infants of inadequate intake of vitamins D and K. Breast milk contains the PUFA needed by term infants who are able to synthesize the long-chain PUFA soon after birth. Pre-term infants fed formulae need supplementation with n3 and n6 long-chain PUFA, since formulas currently do not contain these acids. More work is needed to determine the requirements for n3 and n6 fatty acids, expressed as weights per kilogram. A larger data base using improved analytical procedures to study the nature and content of lipids in human milk is needed. The impact of maternal genetics and diet on fatty acids in milk should be studied, as well as the effect of maternal diet on eicosanoids secreted by the mammary gland. Information on the structure and function of the milk fat globule and its membrane is needed. Little is known about the effect of milk banking on milk lipids. The reader of this review will no doubt find other gaps in our knowledge of the lipid composition and nutritional value of milk that require additional investigation.

Fatty Acids↗
PubMed1991

Purification and characterization of large and small subunits of ribulose 1,5-bisphosphate carboxylase expressed separately in Escherichia coli.

Procedures were developed for 95 and 80% purification to homogeneity of the large subunit (L) and small subunit (S) of ribulose 1,5-bisphosphate carboxylase/oxygenase (L8S8) from Synechococcus PCC 6301, each expressed separately in Escherichia coli. Purified L had a low specific activity in the absence of S (0.075 mumol CO2 fixed/mg holoenzyme/min). Following elution on a Pharmacia Superose 6 or 12 gel filtration column, 50% of the purified L appeared as the octamer, L8. The rest was in equilibrium with lower polymeric species and/or was retained on the column. Large and small subunits assembled rapidly into the L8S8 holoenzyme that had high specific activities, 6.2 and 3.1 mumol CO2 fixed/mg holoenzyme/min for the homologous Synechococcus L8S8 and the hybrid Synechococcus L-pea S L8S8, respectively. The CO2 dependence for carbamylation of L8 was compared to that of L8S8 as a function of pH and CO2 concentration. The pH dependence indicated an apparent pKa for L8 of 8.28 and for L8S8 of 8.15, suggesting that S may influence the pKa of the lysine involved in carbamylation. The Kact for CO2 at pH 8.4 were similar for L8 (13.5 microM) and L8S8 (15.5 microM). L8 bound 2-[14C]carboxy-D-arabinitol 1,5-bisphosphate (CABP) tightly so that most of the bound [14C]CABP survived gel filtration. A major amount of the L8-[14C]CABP complex appeared as larger polymeric aggregates when eluted in the presence of E. coli protein.

Chromatography, Ion Exchange↗
PubMed1991

Modulation of the tight binding of carboxyarabinitol 1,5-bisphosphate to the large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase.

The large subunit (L) of ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) from Synechococcus PCC 6301 was expressed in Escherichia coli, purified as the octamer L8, and analyzed for its ability to tightly bind the transition state analog, 2-carboxyarabinitol 1,5-bisphosphate (CABP). [14C]CABP remained tightly bound to L8 after challenging with [12C]CABP and gel filtration, indicating that L8 alone without the small subunit (S) could tightly bind CABP. Binding of CABP to L8 induced a shift in the gel filtration profile due to apparent aggregation of L8. Aggregation did not occur with the L8S8-CABP complex nor with L8-CABP in the presence of 150 mM MgCl2. If ionic strength was increased with either KCl or MgCl2 during or after the binding of [14C]CABP to L8, [14C]CABP in the complex exchanged with [12C]CABP and was lost from the protein. Ionic strength strongly affected the rate constant (k4) for [14C]CABP dissociation from the L8-[14C]CABP complex, but had little effect on k4 for the L8S8-CABP complex. The differences in CABP binding characteristics between the L8-CABP and L8S8-CABP complexes demonstrate that S is intimately involved in maintaining the stability of the tight binding of CABP to the active site. These are the same interactions stabilizing the intermediate, 3-keto-2-carboxyarabinitol 1,5-bisphosphate, to native rubisco during CO2 fixation.

Binding Sites↗
PubMed1991

Xylulose 1,5-Bisphosphate Synthesized by Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase during Catalysis Binds to Decarbamylated Enzyme.

Xylulose 1,5-bisphosphate (XuBP) is synthesized from ribulose 1,5-bisphosphate (RuBP) at carbamylated catalytic sites on ribulose 1,5-bisphosphate carboxylase (Rubisco) with significant amounts of XuBP being formed at pH less than 8.0. XuBP has been separated by high performance liquid chromatography and identified by pulsed amperometry from compounds bound to Rubisco during catalysis with the purified enzyme and from celery (Apium graveolens var Utah) leaf extracts. XuBP does not bind tightly to carbamylated sites, but does bind tightly to decarbamylated sites. Upon incubation of fully activated Rubisco with 5 micromolar XuBP, loss of activator CO(2) occurred before XuBP bound to the enzyme catalytic sites, even in the presence of excess CO(2) and Mg(2+). Binding of XuBP to decarbamylated Rubisco sites was highly pH dependent. At pH 7.0 and 7.5 with 10 millimolar MgCl(2) and 10 millimolar KHCO(3), the apparent dissociation constant for XuBP, K(d), was 0.03 micromolar, whereas at pH 8.0 and 8.5, the apparent K(d) was 0.35 and 2.0 micromolar, respectively. This increase in K(d) with pH was a result of a decrease in the association rate constant and an increase in the dissociation rate constant of XuBP bound to decarbamylated sites on Rubisco. The K(d) of 2-carboxyarabinitol 1-phosphate binding to carbamylated sites was only slightly pH dependent.

Journal Article↗
PubMed1991

Fallover of Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase Activity : Decarbamylation of Catalytic Sites Depends on pH.

Loss of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity during CO(2) fixation, called fallover, occurred with or without loss of activator CO(2) from catalytic sites depending on pH. At pH 7.5, but not at pH 8.5, the fraction of Rubisco sites that were carbamylated decreased during fallover. Inhibitors which formed during fallover were identified following NaBH(4) reduction and separation of the products by high performance anion-exchange chromatography and pulsed amperometric detection. They were xylulose 1,5-bisphosphate (XuBP) and 3-ketoarabinitol 1,5-bisphosphate. During fallover at pH 8.5, 3-ketoarabinitol-P(2) was the only inhibitor binding to Rubisco and this binding was at carbamylated sites, although both inhibitors were made. At pH 7.5, both inhibitors were bound to catalytic sites of Rubisco with XuBP bound tightly to decarbamylated sites, whereas 3-ketoarabinitol-P(2) bound to carbamylated sites. The pH during fallover also influenced the ratio of 3-ketoarabinitol-P(2) to XuBP formed. When fallover occurred at pH 7.5, both the formation of XuBP and its binding affinity to decarbamylated Rubisco sites were increased compared with those at pH 8.5. 3-Ketoribitol-P(2) was not found at either pH.

Journal Article↗