Comparative properties of microsomes from cow's milk and from mammary gland. 1. Enzymic activities

Bailie, Margot J.; Morton, R. K.

doi:10.1042/bj0690035

Cited by 68 publications

(9 citation statements)

References 21 publications

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“…Although they consist 99% of triglyceride (11), the fat globules in the milk are stable in a water medium because of the presence of interfacial or membranous material. This material has been isolated and identified as "lipoprotein" (11), and it was given (1,19) the designation of "milk microsomes." Patton et al (20) corroborated these findings and suggested that the milk globule membrane is derived from microsomes which are similar to cellular microsomes.…”

Section: Discussionmentioning

confidence: 99%

Lipid Synthesis, Intracellular Transport, and Secretion

Stein

1967

The Journal of Cell Biology

123

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In the mammary glands of lactating albino mice injected intravenously with 9, 10-oleic acid-3 H or 9,10-palmitic acid-5 H, it has been shown that the labeled fatty acids are incorporated into mammary gland glycerides. The labeled lipid in the mammary gland min after injection was in esterified form ( > 95%), and the radioautographic reaction was seen over the rough endoplasmic reticulum and over lipid droplets, both intracellular and intraluminal. At 10-60 min after injection, the silver grains were concentrated predominantly over lipid droplets. There was no concentration of radioactivity over the granules in the Golgi apparatus, at any time interval studied. These findings were interpreted to indicate that after esterification of the fatty acid into glycerides in the rough endoplasmic reticulum an in situ aggregation of lipid occurs, with acquisition of droplet form. The release of the lipid into the lumen proceeds directly and not through the Golgi apparatus, in contradistinction to the mode of secretion of casein in the mammary gland or of lipoprotein in the liver. The presence of strands of endoplasmic reticulum attached to intraluminal lipid droplets provides a structural counterpart to the milk microsomes described in ruminant milk INTRODUCTION

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Section: Discussionmentioning

confidence: 99%

Lipid Synthesis, Intracellular Transport, and Secretion

Stein

1967

The Journal of Cell Biology

123

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“…The origin of de-molybdo-xanthine oxidase was investigated. FAD/Mo ratios show that it is present not only in enzyme purified by conventional methods but also in 'milk microsomes' (Bailie & Morton, 1958) and in enzyine samples prepared without proteolytic digestion. We conclude that it is secreted by cows together with the active enzyme and we discuss its occurrence in the preparations of other workers.…”

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confidence: 98%

“…'Microsomes' were isolated from this by the method given in Fig. 2 of Bailie & Morton (1958) except that the washing and suspension medium was 0.15M-NaCl containing 1 mmsodium salicylate. The procedure was taken to stage 'Ml and M2' of their method.…”

mentioning

confidence: 99%

The composition of milk xanthine oxidase

Hart

McGartoll

Chapman

et al. 1970

Biochemical Journal

163

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The composition of milk xanthine oxidase has been reinvestigated. When the enzyme is prepared by methods that include a selective denaturation step in the presence of sodium salicylate the product is obtained very conveniently and in high yield, and is homogeneous in the ultracentrifuge and in recycling gel filtration. It has specific activity higher than previously reported preparations of the enzyme and its composition approximates closely to 2mol of FAD, 2g-atoms of Mo and 8g-atoms of Fe/mol of protein (molecular weight about 275000). In contrast, when purely conventional preparative methods are used the product is also homogeneous by the above criteria but has a lower specific activity and is generally comparable to the crystallized enzyme described previously. Such samples also contain 2mol of FAD/mol of protein but they have lower contents of Mo (e.g. 1.2g-atom/mol). Amino acid compositions for the two types of preparation are indistinguishable. These results confirm the previous conclusion that conventional methods give mixtures of xanthine oxidase with an inactive modification of the enzyme now termed ;de-molybdo-xanthine oxidase', and show that salicylate can selectively denature the latter. The origin of de-molybdo-xanthine oxidase was investigated. FAD/Mo ratios show that it is present not only in enzyme purified by conventional methods but also in ;milk microsomes' (Bailie & Morton, 1958) and in enzyme samples prepared without proteolytic digestion. We conclude that it is secreted by cows together with the active enzyme and we discuss its occurrence in the preparations of other workers. Studies on the milks of individual cows show that nutritional rather than genetic factors determine the relative amounts of xanthine oxidase and de-molybdo-xanthine oxidase. A second inactive modification of the enzyme, now termed ;inactivated xanthine oxidase', causes variability in activity relative to E(450) or to Mo content and formation of it decreases these ratios during storage of enzyme samples including samples free from demolybdo-xanthine oxidase. We conclude that even the best purified xanthine oxidase samples described here and by other workers are contaminated by significant amounts of the inactivated form. This may complicate the interpretation of changes in the enzyme taking place during the slow phase of reduction by substrates. Attempts to remove iron from the enzyme by published methods were not successful.

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“…Figure 2 demonstrates the vesicular structure of the PLP, a morphology characteristic of liposomes. Addition of the surfactants, Triton X-100 or Tween 80, produced the same increase in enzyme activity ascribable to the rupture of the liposomal membrane and subsequent release of the entrapped enzyme (13). Addition of the surfactants, Triton X-100 or Tween 80, produced the same increase in enzyme activity ascribable to the rupture of the liposomal membrane and subsequent release of the entrapped enzyme (13).…”

Section: Milk Fractions Illustrated Inmentioning

confidence: 86%