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Biomedical subjects

R G Jensen

Publications and source records attributed to R G Jensen.

At least 91 records · Page 5Linked to original sources
PubMed1981

Ribulose 1,5-bisphosphate and activation of the carboxylase in the chloroplast.

Ribulose 1,5-bisphosphate in the chloroplast has been suggested to regulate the activity of the ribulose bisphosphate carboxylase/oxygenase. To generate high levels of ribulose bisphosphate, isolated and intact spinach chloroplasts were illuminated in the absence of CO(2). Under these conditions, chloroplasts generate internally up to 300 nanomoles ribulose 1,5-bisphosphate per milligram chlorophyll if O(2) is also absent. This is equivalent to 12 millimolar ribulose bisphosphate, while the enzyme, ribulose bisphosphate carboxylase, offers up to 3.0 millimolar binding sites for the bisphosphate in the chloroplast stroma. During illumination, the ribulose bisphosphate carboxylase is deactivated, due mostly to the absence of CO(2) required for activation. The rate of deactivation of the ribulose bisphosphate carboxylase was not affected by the chloroplast ribulose bisphosphate levels. Upon addition of CO(2), the carboxylase in the chloroplast was completely reactivated. Of interest, addition of 3-phosphoglycerate stopped deactivation of the carboxylase in the chloroplast while ribulose bisphosphate accumulated. With intact chloroplasts in light, no correlation between deactivation of the carboxylase and ribulose bisphosphate levels could be shown.In contrast, incubation of purified ribulose bisphosphate carboxylase with ribulose bisphosphate irreversibly inhibited activation, especially in the absence of CO(2). Addition of the same amount of ribulose bisphosphate to lysed chloroplasts did cause some deactivation of the carboxylase in the extract, but full activation returned when the ribulose bisphosphate was consumed. The ribulose bisphosphate carboxylase in the chloroplast is not irreversibly inhibited by high levels of ribulose bisphosphate.

Journal Article↗
PubMed1980

Composition of the lipids in human milk: a review.

Recent publications on the composition of human milk are reviewed. The importance of proper sampling is discussed. Fat contents of 2.6-4.5% and cholesterol amounts of 200-650 mg/100 g fat were reported. The phytosterols in milk were increased by the consumption of these sterols. Phytosterols could contribute to the "total cholesterol" in milk if analyses are done colorimetrically. The fatty acid composition is remarkably uniform unless bizarre diets are consumed; the amounts of linoleic acid vary the most. Phospholipids contained more long chain polyunsaturated fatty acids than triacylglycerols.

Animals↗
PubMed1980

Effect of chronic ingestion of DDT on physiological and biochemical aspects of essential fatty acid deficiency.

Male weanling rats were fed semipurified diets with and without essential fatty acid (EFA) and DDT (150 ppm) for 14 weeks to determine the effects of the pesticide on physiological and biochemical aspects of EFA deficiency (EFAD). DDT did not affect EFAD-induced reduction in growth rate of final body weight, nor did the pesticide affect EFAD-induced changes in feed efficiency or skin dermatitis. The pesticide did increase liver/body mass ratios, but did not interact with EFAD, which also increased this ratio. The pesticide produced complex changes in total fatty acid composition of liver and tail skin; liver levels of 18:0, 18:2 and 20:3 omega 9 were increased, whereas levels of 12:0, 14:0 and 16:0 were decreased. In both tissues, DDT interacted with EFA to increase 18:2 levels. DDT did not change the total fatty acid 20:3 omega 9/20:4 omega 6 ratio in either tissue. In this study, although DDT did not exacerbate the physiological aspects of EFAD, DDT-induced changes in fatty acid composition of liver and tail skin indicated that 150 ppm DDT in the diets did alter lipid metabolism of the rats in an unexplained manner.

Animals↗
PubMed1979

Cholesteryl ester and triacylglycerol fatty acids in type V hyperlipidemia.

The fatty acid compositions of plasma cholesteryl esters (CF) and triacylglycerols (TG) from seven healthy individuals and five patients with type V hyperlipoproteinemia were determined. Very low density (VLDL), low density (LDL) and high density lipoproteins (HDL) wer isolated. The lipids were extracted from the lipoproteins and the triacylglycerols and cholesteryl esters separated for analysis. The fatty acid compositions of triacylglycerols from healthy and type V individuals were very similar. The cholesteryl esters from type V patients had increased contents of palmitic and decreased amounts of linoleic and arachidonic acids as compared to the normal individuals. The fatty acid composition of the cholesteryl esters from high density lipoproteins had the greatest deviation. The fatty acid compositions of the triacylglycerols from the two groups were similar. However, the triacylglycerols in all lipoprotein fractions contained more palmitic and oleic and less linoleic and arachidonic acids than the cholesteryl esters.

Adult↗
PubMed1979

Measurement of ribulose 1,5-bisphosphate from spinach chloroplasts.

A technique has been developed for the rapid and simple measurement of ribulose 1,5-bisphosphate from isolated spinach chloroplasts. The endogenous ribulose bisphosphate was detected enzymically using (14)CO(2) and ribulose bisphosphate carboxylase/oxygenase released from the chloroplasts. Ribulose 5-phosphate kinase was inhibited with 0.4 to 0.6 millimolar 2,6-dichlorophenol-indophenol and 4 micromolar carbonyl cyanide m-chlorophenylhydrazone. Phosphoenolpyruvate carboxylase activity was low with washed chloroplasts and its labeled product, [(14)C]oxalacetate, was destroyed by heating with 1.0 n HCl at 90 C. The assay method was linear from 0.05 to 0.87 nanomoles ribulose bisphosphate per milliliter. The latter value was determined with chloroplast material having 44 micrograms of chlorophyll per milliliter. This technique was simple and direct, used less chloroplast material, yet provided results comparable to a previously described enzymic technique in which ribulose bisphosphate was determined after the precipitation of chloroplast proteins by perchloric acid.

Journal Article↗
PubMed1979

Photosynthesis and ribulose 1,5-bisphosphate levels in intact chloroplasts.

The response of ribulose 1,5-bisphosphate levels and CO(2) fixation rates in isolated, intact spinach chloroplasts to pyrophosphate, triose phosphates, dl-glyceraldehyde, O(2), catalase, and irradiance during photosynthesis has been studied. Within 1 minute in the light, a rapid accumulation of ribulose bisphosphate was measured in most preparations of intact chloroplasts, and this subsequently dropped as CO(2) fixation increased. Pyrophosphate, triose phosphates, and catalase increased CO(2) fixation and also the levels of ribulose bisphosphate. CO(2) fixation was inhibited by dl-glyceraldehyde and O(2) with corresponding decreases in ribulose bisphosphate. When the rate of photosynthesis decreased at limiting irradiances (low light), the level of ribulose bisphosphate in the chloroplast did not always decrease, suggesting that ribulose bisphosphate was not limiting CO(2) fixation under these conditions. When triose phosphates (fructose bisphosphate plus aldolase) were added to suspensions of chloroplasts at low irradiances, ribulose bisphosphate increased while CO(2) fixation decreased. These observations provide considerable evidence that high ribulose bisphosphate levels clearly are not solely sufficient to permit rapid rates of CO(2) fixation, but that factors other than ribulose bisphosphate concentration are overriding the control of photosynthesis.Isolated chloroplasts are capable of using carbon reserves to produce considerable ribulose bisphosphate. Upon illumination in the absence of CO(2) and O(2), intact chloroplasts produced up to 13 millimolar ribulose bisphosphate.

Journal Article↗
PubMed1978

Lipids of human milk and infant formulas: a review.

The amount of human milk ingested by the nursing infant is about 600 ml per day. The average lipid content of the mature ranges from 3.2 to 3.5% and the amount does not appear to be influenced by diet. About 98% of the lipid is triacylglycerol in which most of the secondary ester is palmitic acid, a unique structure possibly responsible for the relatively high absorbability of the fat. Small quantities of other lipids are present. Amounts of cholesterol reported, range from 200 to 564 mg per 100 g of lipid. While 167 fatty acids have been positively and tentatively identified as being present in human milk lipids, the major fatty acids are palmitic, stearic, oleic, and linoleic. The composition can be changed by diet, which linoleic acid contents of from 1.0 to 45.0% having been found. The "average" linoleic acid is about 10% and this amount is apparently adequate for the essential fatty acid requirements of the infant. The quantity of vitamin E also appears to be satisfactory. The hypothesis that a cholesterol challenge to the breast fed infant would enable the adult to more efficiently metabolize the sterol does not seem to be supported by available evidence, primarily, because the cholesterol content of human milks varies so markedly; 26 to 52 mg per 8 ounces. The compositions of most infant formulas currently in use in the United States are presented for comparison and convenience and a few possible problems associated with their consumption are discussed. We have suggested several areas where, in our opinion, additional research would provide useful information.

Animals↗
PubMed1977

Glycerol ester hydrolase activity in the pulp of unerupted calves' teeth.

The pulp from unerupted calves' teeth was found to contain low levels of glycerol ester hydrolase activity. Solutions in Tris buffer cleared tributyrylglycerol agar and hydrolyzed emulsified olive oil. The average quantity of free fatty acids released in five assays with olive oil was: 2.8, S.D.+/-1.4. Specific activities were: 0.25, S.D.+/-0.13, mkatals/kg protein.

Animals↗
PubMed1977

Pregastric esterase and other oral lipases--a review.

The secretion of pregastric esterase and other oral lipases has been detected in 13 species. Research on secretion by the human, calf, kid goat, lamb, and rat of pregastric esterase has been significant. Secretion by calves is little affected by age or diet but is greater when calves are nipple fed than when pail fed. Whole milk sham-fed to calves exhibits immediate, sharp decreases in pH and rennet coagulation time resulting from liberation of free fatty acids by pregastric esterase. Bacterial counts in sham-fed products are higher than in control (nonfed) products, but during subsequent incubation bacterial numbers increase less rapidly in sham-fed products. Calf pregastric esterase is a major fat digestive enzyme in young calves but gradually becomes subsidiary to pancreatic lipase as secretion of the latter develops with age. Calf, kid goat, and lamb pregastric esterase exhibits optimum activity on milk fat but is capable of splitting other dietary fats. Data on oral and "gastric" lipases in calves, humans, and rats suggests that gastric lipase is oral lipase. Data on pH and temperature optima as well as activation and inhibition of oral lipases is contradictory but appears to vary considerably between species. Calf pregastric esterase exhibits a unique specificity for fatty acids 4:0 to 10:0 and preferentially hydrolyzes the primary ester position of glycerin. Preparations of calf, kid goat, and lamb pregastric esterase are used commercially to impar typical flavors to Italian-type and Feta cheeses and to accelerate flavor development in other cheeses and cheese-like products. Butterfat modified by pregastric esterase is utilized to impart dairy flavor character to a wide range of processed foods. Treatment with pregastric esterase of calf scours and human malabsorption of syndrome also has been reported.

Abomasum↗
PubMed1975

Effect of diet on fatty acids in the lipoprotein cholesteryl esters of type IIa and normal individuals.

Four normal and two individuals with type IIa hyperlipoproteinemia were placed on the National Heart and Lung Institute Type IIa Diet (less than 300 mg of cholesterol per day, high polyunsaturated, low saturated fat diet) for 1 week and on a normal diet the following week. Plasma samples were obtained and the cholesterol contents of plasma and of very low density, low density and high density lipoproteins determined. The cholesteryl esters in one type IIa and two normal individuals were identified. The cholesteryl esters in type IIa very low density lipoproteins from blood drawn 45 min after the last meal in each dietary period, contained less 18:2 than from the normal. After the first dietary period, the very low density lipoprotein cholesteryl ester 18:2 content for the type IIa was 37.2M% and for the normals, 54.7M%. After the second dietary period, the corresponding values were 49.7M% and 56.7M%. Fasting samples had lower 18:2 contents in the low density lipoproteins from the Type IIa subject following both dietary periods and in the high density lipoproteins following the Type II diet.

Cholesterol↗
PubMed1975

Effects of diet and type IIa hyperlipoproteinemia upon structure of triacylglycerols and phosphatidyl cholines from human plasma lipoproteins.

Four normal and two individuals with Type IIa hyperlipoproteinemia were placed on the National Heart and Lung Institute Type IIa diet (low cholesterol, smaller than 300 mg/day, high polyunsaturated, low saturated fat diet) for 1 week and on a normal diet the following week. Plasma samples were obtained and the triacylglycerols, phospholipids, and cholesterol contents of plasma and of very low density lipoproteins, low density lipoproteins, and high density lipoproteins determined. Triacyglycerol fatty acid composition was determined and stereospecific analyses of triacglycerols and phosphatidyl cholines performed. Structural determinations were limited to one normal and one Type IIa individual. In normal and Type IIa individuals, chylomicrons contained twice the amount of 18:0 as did the very low density lipoproteins, low density lipoproteins, or high density lipoproteins. The structure of the triacyglycerols from the very low density lipoproteins and low density lipoproteins was asymmetric with at least 50M% 16:0 in the sn-1 position and mostly 18:1 in positions sn-2 and 3. There was a marked difference in the distribution of 18:2 in low density lipoproteins of the normal and Type IIa individuals. The control contained equal amounts of 18:2 in the sn-1 and sn-3 positions, whereas IIa low density lipoprotein was asymmetric with 26% of the 18:2 in position sn-1 and 3% in the sn-3 position. Very low density lipoprotein was asymmetric with regard to 18:2 in control and IIa samples with an average of 5% of the 18:2 in position sn-1 and 40% in position sn-3. The phosphatidyl cholines contained predominantly 16:0 and 18:0 in position sn-1, whereas the acids in position sn-2 were unsaturated with very little difference between lipoprotein classes. Neither the short dietary periods nor source of plasma affected the structure of the phosphatidyl cholines.

Dietary Fats↗