The effect of temperature on a reaction catalysed by lactose synthetase<i>A</i> protein

Kitchen, Barry J.; Andrews, P.

doi:10.1016/0014-5793(72)80605-7

Cited by 13 publications

(2 citation statements)

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“…Studies of such vesicles in crude and in purified preparations have shown that they contain soluble a-lactalbumin in contact with a galactosyltransferase (EC 2.4.1.22) that is attached to the membrane with its active site facing the lumen (Brodbeck & Ebner, 1966a;Coffey & Reithel, 1968a,b;Jones, 1972;Kuhn & White, 1975, 1977. Separate experiments with the soluble galactosyltransferase of bovine and human milk have shown that a-lactalbumin is essential for the galactosylation of glucose but is generally unnecessary, or in certain cases even inhibitory, for the galactosylation of N-acylglucosamines (Brodbeck & Ebner, 1966b;Brew et al, 1968;Schanbacher & Ebner, 1970; Kitchen & Andrews, 1972;Kuhn et al, 1980). When the substrates glucose and UDPgalactose are added to suspensions of vesicles they apparently penetrate the membrane to reach the active site of the enzyme, but the product lactose is mostly retained within the lumen.…”

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confidence: 99%

Effects of phlorrhizin and thiol reagents on the galactosyltransferase activity of Golgi membrane vesicles of lactating rat mammary gland

Kuhn¹,

White²

1980

Biochemical Journal

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1. The ability of phlorrhizin to inhibit the galactosylation of glucose was re-examined with Golgi membrane vesicles purified from rat mammary gland, and extended to the galactosylation of several glucose analogues and N-acylglucosamines. 2. The inhibition is ascribed, contrary to previous conclusions, to a general annealing of leaky membranes comprising a minority of the vesicles. 3. Three thiol reagents were able to inhibit the galactosylation of N-acylglucosamines with less, or no, inhibition of galactosylation of glucose. This demonstrates the existence of a Golgi membrane carrier that distinguishes between glucose and N-acylglucosamines.

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confidence: 99%

Effects of phlorrhizin and thiol reagents on the galactosyltransferase activity of Golgi membrane vesicles of lactating rat mammary gland

Kuhn¹,

White²

1980

Biochemical Journal

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“…Lactose synthase enzyme activity has been studied for a long time, which revealed that the appropriate temperature for the galactosyltransferase was lower than is usual for enzymes. The maximum activity of this enzyme was at 24 °C (Kitchen and Andrews, 1972). However, it is widely known that the appropriate temperature for the lactose synthesis enzyme is 37 °C (Watkins and Hassid, 1962).…”

Section: Mammary Gland Functionmentioning

confidence: 98%

Akt expression and lactose synthesis during heat exposure in Saanen goat

Saipin¹,

สายปิ่น²,

Thammacharoen³

et al.

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In tropical countries, high ambient temperature (HTa) is a fundamental factor that cause a decline in the mammary gland function in dairy animals. Dairy animals fed under HTa decreased milk yield (MY) as well as milk compositions. The current study focuses on the effect of HTa to decrease milk synthesis from natural and in vitro HTa condition. The first experiment was performed to investigate the effect of HTa from the natural condition in early lactating Saanen goat, 2-4 weeks of postpartum (2 PP-4 PP). Five animals were investigated during the winter season as control ambient condition. Six animals as the natural HTa group was conducted during summer. The environmental conditions, rectal temperature (Tr), respiratory rate (RR), dry matter intake (DMI) and MY were measured everyday throughout the experiment. At the end of 2 PP and 3 PP, blood and milk samples were collected to measure blood glucose, oxidative stress status, and milk composition. In addition, the milk cells were isolated from milk sample to evaluate gene expression. The second experiment was performed using mammary epithelial cells (MECs) culture isolated from goat milk to investigate the effect of HTa on lactose synthesis and oxidative stress status of MECs culture. The cells were allocated into two temperature groups that were 37 ºC as the control and 39 ºC as the HTa group. After 1- and 48-hour incubation the culture medium was collected for measured lactose concentration and MECs were harvested to determine gene expression, respectively. In the first experiment, the average ambient temperature (Ta), relative humidity (RH), temperature humidity index (THI), and RR were significantly increased in summer when compared with the winter season. In both seasons Tr in the afternoon and evening was significantly higher than that in the morning. However, Tr from summer was not significantly different from winter. Whereas, DMI and MY during the winter group showed significantly higher than that from the summer group. In the present study, during summer, plasma glutathione peroxidase (GPx) activity in the afternoon were significantly higher than that in winter. Whereas, plasma cortisol in the afternoon was significantly higher than that in the morning in both seasons. Moreover, the relative gene expressions of α-lactalbumin (α-LA) and heat shock protein 70 (HSP70) gene were higher in summer when compared with the winter season. However, there were no differences between the season on the relative expression of β-1,4-galactosyltransferase (β-GALT1) and Akt genes. The results suggested that the natural ambient condition from the present experiment showed high temperature and humidity index especially during the afternoon in both winter and summer months. The effect of HTa on milk synthesis might be related to an increase in antioxidative capacity of the goats and expression of HSP70 gene but this effect is not related to Akt expression. In the second experiment, the results of the relative gene expression of HSP70 increased significantly after 1 hour HTa incubation when compared with the control. At 1 or 48 hours incubation, HTa condition could not affect β-GALT1 and α-LA genes expression as well as Akt. In addition, there was no difference in lactose concentration between control and HTa group. These results showed that HTa did not influence lactose synthesis gene expression of MECs. In conclusion, the effect of HTa on MY and MECs culture apparently related with increasing expression of HSP70 from both natural and in vitro study. However, HTa did not affect the expression of β-GALT1, α-LA and Akt genes.

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Lactose Synthetase

Hill

Brew

1975

Advances in Enzymology - And Related Areas of Molecular Biology

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The effect of temperature on a reaction catalysed by lactose synthetaseA protein

Cited by 13 publications

References 10 publications

Effects of phlorrhizin and thiol reagents on the galactosyltransferase activity of Golgi membrane vesicles of lactating rat mammary gland

Effects of phlorrhizin and thiol reagents on the galactosyltransferase activity of Golgi membrane vesicles of lactating rat mammary gland

Akt expression and lactose synthesis during heat exposure in Saanen goat

Lactose Synthetase

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