Zur Verdauungsphysiologie des Säuglings

Freudenberg, E.

doi:10.1007/bf02225516

Cited by 25 publications

(4 citation statements)

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“…Conversely, our pK, values of 8.33 and 8.40 agree with that calculated from the data of Jubelin and Boyer olX.31, but not with that calculated from the data of Hernell and Olivecrona of ca. 10.6. In a more recent publication, Hernell [I] noted that at pH > 9 there is induced some destruction of the enzyme and so this last value must be viewed with caution.…”

Section: Ionization Of' Esseti T I D Rrsiduesmentioning

confidence: 99%

Studies in bile salt solutions

O’Connor

Wallace

1984

European Journal of Biochemistry

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The pseudo-first-order rate constants of hydrolysis of p-nitrophenylacetate, catalyzed by human milk lipase, have been measured in solutions of 0.01 mol dm-3 Bistris(2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-propane-l,3-diol) buffer at 310.5 K , containing a range of concentrations of sodium taurocholate and sodium cholate, at pH 8.00 and of sodium cholate at pH 6.5. The effect of pH on the activity of the enzyme has been investigated and the stimulation factors of taurocholate and cholate ions and of cholic acid have been calculated to be equal to 5.3. 3.7 and 10.7, respectively. The essential residues for catalytic activity of the enzyme have ionization constants equal to 6.45 -6.46 for pK, and 8.33 -8.40 for pK,. The former value is attributed to the presence of a histidine imidazolium group but the identity of the residue leading to pK, is not proven.Human milk lipase comprises 1 % of the protein in human milk and is inactive against milk fats in the breast. In the presence of bilc salts in the small intestine, its lipolytic activity is stimulated to a degree which is dependent upon the identity and concentration of the substrate [I -121. Because of this property the enzyme has also been called bile-salt-stimulated lipase and bile-activated lipase. Recent studies have implicated human milk lipase as a novel microbicidal agent, capable of rapidly killing Giurdiu lumbilci, a common pathogenic intestinal parasite of humans, by exposure to normal human milk in uitro [13]. Thus human milk may play a protective role in infants exposed to this parasite.Human milk lipase has been shown to survive pH and enzymatic conditions approximating passage through an infant's stomach [l,5]. The optimal activity range has been determined as pH 6 -8 for human milk lipase unstimulated hydrolysis of tributylglyceride and ca. pH 9.5 in the presence of 6 mM sodium taurochloate and between pH 7.5 and 8.5 for both stimulated (3 mM sodium taurocholate) and unstimulated hydrolysis of p-nitrophenylacetate [5], while an optimal pH of ca. 8 has been noted for stimulated (10 mM sodium taurocholate) human milk lipase for both trioleylglyceride and tributylglyceride [I 41.Under favorable circumstances, pH studies can yield useful information to distinguish between the often complex effects of pH variation on enzyme-catalyzed reactions. Such studies led to useful deductions about the nature of the binding between bile salts and porcine pancreatic lipase [I 51. But if the data are to be easily interpreted it is essential that only a limited number of interactions be affected by the change in pH. Previous investigations [5,14] have shown that use of the oilphase-soluble substrate trioleylglyceride has produced two activity/pH profiles of quite difrerent appearance and in the presence of rat pancreatic non-specific lipase [16] it was found that insoluble substrates gave different values of K , and V , for This is part 3 in a series; part 2 appeared elsewhere [l].Abbreuiution. Bistris, 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl-propane-l,3...

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Section: Ionization Of' Esseti T I D Rrsiduesmentioning

confidence: 99%

Studies in bile salt solutions

O’Connor

Wallace

1984

European Journal of Biochemistry

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“…5, No . 4,1986 aci d pr oduced by th e pathway du e to cat alysis by th e un st imulated enzy me inc reases . Source s of substrate that thi s un stimulated enzy me co uld hydrol yze in milk would be the va rious retinol es te rs (29), sho rt-cha in tri acylglycerols (30,3 I) , and longchain di-and mono-oleylglycerol (32,33).…”

Section: Discussionmentioning

confidence: 99%

“…5, No. 4,1986 the surface of the enzyme in its original conformation, even under conditions where another region (i.e., the esterolytic site) undergoes an inactivating conformational change. Others have found that the binding (or template) effect of bile salts exerts a stabilizing influence (37).…”

Section: Discussionmentioning

confidence: 99%

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Inactivation of Bile‐Salt‐Stimulated Human Milk Esterase

O'Connor,

Longbottom,

Walde

1986

J. pediatr. gastroenterol. nutr.

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SummaryThe activity of bile‐salt‐stimulated esterase was monitored in human milk during storage at room temperature, in a refrigerator (4°C), in a freezer (‐ 19°C), and in milk that had been freeze dried and rehydrated after storage of the lypophilized milk at 4°C and ‐ 19°C. In all cases, there was some loss of activity, independent of measurement in the presence or absence of sodium taurocholate, and the loss was highest in milk stored at room temperature, approximating a 50% loss in 1–2 days. Activation and inactivation of solutions of the purified enzyme have been identified by measuring its esterase activity against a variety of 4‐nitrophenylalkanoate esters at pH 7.3 within the temperature range 5–46.5°C. The optimum temperature was 42°C. The presence of bile salt partially serves to maintain the conformation of the bile‐salt‐binding site as the esterolytic binding site becomes inactivated at 50°C. Bile salts thus exert a positive template effect on the enzyme.

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Über die Spezifität der Cholin‐esterase‐Hemmung durch Tri‐o‐kresyl‐phosphat

Hottinger

Bloch

1943

Helvetica Chimica Acta

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Zur Verdauungsphysiologie des Säuglings

Cited by 25 publications

References 5 publications

Studies in bile salt solutions

Studies in bile salt solutions

Inactivation of Bile‐Salt‐Stimulated Human Milk Esterase

Über die Spezifität der Cholin‐esterase‐Hemmung durch Tri‐o‐kresyl‐phosphat

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