scholarly journals Kinetics of liver microsomal cholecalciferol 25-hydroxylase in vitamin D-depleted and -repleated rats

1978 ◽  
Vol 172 (3) ◽  
pp. 417-422 ◽  
Author(s):  
E E Delvin ◽  
A Arabian ◽  
F H Glorieux
Keyword(s):  
Vitamin D ◽  
Rat Liver ◽  
Vitamin D Intake ◽  
No Inhibition ◽  
Normal Vitamin ◽  
Kinetics Of ◽  
Cytochrome P 450 ◽  
Generating System

Kinetics of vitamin D-depleted and -repleted rat liver microsomal cholecalciferol 25-hydroxylase were studied. Anaerobiosis, CO, omission of a NADPH-generating system and addition of detergents all decreased the activities, showing that the hydroxylase behaves like a cytochrome P-450-dependent enzyme. An apparent Km of 0.18 micrometer and Vmax. of 32pmol/min per g of tissue were found for vitamin D-deficient animals. Although both apparent Km and Vmax. were significantly altered in vitamin D-repleted animals no inhibition of the enzyme was elicited. These latter results show that at normal vitamin D intake, rat liver cholecalciferol 25-hydroxylase is not feedback-inhibited.

Reduction kinetics of purified rat liver cytochrome P-450. Evidence for a sequential reaction mechanism dependent on the hemoprotein spin state

Biochemistry ◽  
1984 ◽  
Vol 23 (20) ◽  
pp. 4526-4533 ◽  
Author(s):  
Paul P. Tamburini ◽  
G. Gordon Gibson ◽  
Wayne L. Backes ◽  
Stephen G. Sligar ◽  
John B. Schenkman
Keyword(s):  
Reaction Mechanism ◽  
Rat Liver ◽  
Spin State ◽  
Reduction Kinetics ◽  
Sequential Reaction ◽  
Liver Cytochrome ◽  
Kinetics Of ◽  
Cytochrome P 450

Vitamin D - From Essentiality to Functionality

2012 ◽  
Vol 82 (5) ◽  
pp. 321-326 ◽  
Author(s):  
Heike Bischoff-Ferrari
Keyword(s):  
Vitamin D ◽  
Vitamin D Deficiency ◽  
Serum Levels ◽  
Vitamin D Status ◽  
Hydroxyvitamin D ◽  
Vitamin D Intake ◽  
Severe Deficiency ◽  
Normal Vitamin ◽  
25 Hydroxyvitamin D ◽  
Muscle Health

Vitamin D is essential in bone and muscle health. Severe deficiency (25-hydroxyvitamin D serum levels < 25 nmol/l) can result in rickets and osteomalacia, fractures, myopathy and falls. All recent recommendations on vitamin D agree that children and adults should reach a target 25-hydroxyvitamin D range of at least 50 nmol/l (threshold for normal vitamin D status) and 50 % of the population may be below that threshold. A vitamin D intake of 600 to 800 IU per day as recommended today will prevent about 97 % of children and adults from vitamin D deficiency. Notably, a higher 25-hydroxyvitamin D threshold of more than 60 nmol/l is needed for optimal functionality, fall and fracture in adults age 65 and older.

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