Comparison of 15N-labelled glycine, aspartate, valine and leucine for measurement of whole-body protein turnover

Whole-body protein turnover was measured in rats by constant infusion of 15N-labelled glycine, aspartate, valine and leucine and measuring the enrichment of hepatic and renal urea and ammonia nitrogen. The values obtained with [15N] glycine were comparable with values reported with methods based on different assumptions. [15N] Aspartate gave rise to an increased enrichment of urea and ammonia and hence to lower protein-turnover rates. [15N] Valine and [15N] leucine gave low enrichments of nitrogenous end products and hence to high protein-turnover rates. All 15N-labelled amino acids are not equally suitable for measuring whole-body protein turnover by the end-product method. The relative amounts of 15N going to the end products can be prodicted from the known individual metabolism of aspartate and the branched-chain amino acids (AU)

Haemoglobin Spanish Town alpha27 Glu replaced by Val (B8)

A new alpha chain variant Hb Spanish Town, a27 Glutamic acid-Valine, awas detected in the cord blood of a Jamaica Negro infant. In the mother the adult component (a2 Spanish TownB2) has an electrophoretic mobility between haemoglobins S and F at alkaline pH and measures 11.0-12.0 percent of the total haemoglobin. (Summary)

The catabolism of valine in the malnourished rat: studies in vivo and in vitro with different labelled forms of valine

1. The catabolism of valine was estimated in vivo by measurement of the production of labelled CO2 for 2 h after the oral administration of either [U-14C] valine. It was also estimated in vitro in homogenates of liver and muscle incubated with labelled valine. Experiments were performed in rats given diets providing either 215 g (HP) or 25 g (LP) protein per kg diet. 2. The proportion of [U-14C] valine excreted as 14 CO2 was not reduced in rats given the LP diet for 16 d but the excretion of 14 CO 2 from [1-14C] valine was reduced by 40 percent in these animals. When rats were transferred from the HP diet to the LP diet there was a reduction in the excretion of 14CO2 from [1-14C] valine; when the diet was changed from LP to HP output of 14CO2 increased to control values. 3. Homogenates of muscle and liver catabolized valine to CO2. Both liver and muscle from rats fed on the LP diet catabolized less [1-14C] valine than tissues from control animals. 4. Valine aminotransferase activity was higher in muscle than in liver, and did not change in tissues from rats fed on the LP diet. In these animals 2-ketoisovaleric acid dehydrogenase activity was reduced in both liver and muscle. 5. The production of 14CO2 was lower with [U-14C] valine as the substrate than with [1-14C]-valine and there was no difference between tissues from rats fed on the HP and LP diets. 6. The results with [1-14C] valine suggest that both liver and muscle from protein-depleted rats catabolize valine at a reduced rate. The reason for the discrepancy between these results and those with [U-14C] valine is not clear. It is concluded that the results with [U-14C] valine in vitro are affected by dilution of the label before the formation of 14CO2, but that this does not hold in vivo (AU)

The catabolism of valine in the rat. The effects of protein calorie malnutrition in vivo and in vitro

A striking and consistent finding in the malnourished child is the very low level of valine in the plasma. It has been proposed that unaltered or increased catabolism of valine by skeletal muscle might account for this large reduction in the plasma valine concentration. In support of this hypothesis is the finding that the proportion of uniformly labelled valine (U-1 to 4th power C-valine) which is excretes as CO2 is the same in control and malnourished rats. Much of the label from U-1 to 4th power C-valine has to enter the Krebs cycle in order to be metabolised to CO2 and the results above may reflect the activity of this metabolic pathway. The formation of the labelled CO2 from valine labelled in the carboxylic acid group (1-1 to 4th power C-valine) reflects the activities of the first two enzymes in the catabolic pathway for valine. Malnourished rats excrete a lower proportion of a dose of 1-1 4th power C valine than do control rats. This result suggests that the specific part of the catabolic pathway of valine