Protein catabolism, calcium

A wide range of plasma phosphorus concentration has been observed by other workers in primary hyperparathyroidism (C7) and explained in terms of diet and renal excretion. Unlike the calcium concentration, which is normally very constant regardless of dietary intake and urinary excretion, the concentration of inorganic phosphate in plasma is the resultant of the rate of phosphorus absorption from the gut and protein catabolism, on the one hand, and of renal excretion, on the other. Although the parathyroid hormone promotes phosphorus excretion, this is only one of the factors governing plasma phosphate concentration. Plasma phosphate in cases of hyperparathyroidism on a relatively high phosphorus intake may therefore not be distinguishable from that in normal subjects on a lower intake. 

Calcium/calmodulin-dependent protein kinase II (CaM kinase II) is a mediator of synaptic and cytoskeletal function as well as neurotransmitter release. The reduced CaM kinase II activity observed following normothermic ischemia is not seen under conditions of intraischemic hypothermia (57,110). Ubiquitin, a small protein involved in the catabolism of other abnormal proteins, is decreased following ischemia this may lead to an accumulation of abnormal proteins that affect cell function. Intraischemic hypothermia induces a significant restitution of ubiquitin compared to the normothermic condition (111). 

The mechanism by which dietary protein induces an increase in urinary calcium is not clear, The effect has been attributed, in part, to the catabolism of sulfur-containing amino acids to yield sulfate. Elevated levels of plasma sulfate can form a complex with calcium. The complex passes into the renal tubule, where it is poorly reabsorbed, resulting in its excrehon in the urine. The mechanism by which phosphate reverses the hypercalciuric effect of protein is also not dear. 

Free sulfate occurs in the plasma at concentrations of 1 to 2 mAf, The sulfate in the plasma and glomerular filtrate has been a concern for those interested in calcium status. Consumption of high-protein diets leads to increases in urinary calcium levels. This effect has been attributed, in part, to the catabolism of sulfur amino adds to yield free sulfate. The sulfate forms a complex with the calcium in... 

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