Alkaline phosphatase in normal infants

Alkaline phosphatase was measured in plasma from children receiving vitamin D supplements in day nurseries in the London area, and from children exposed to sunlight in the West Indies. The distribution of values showed that there was no precise upper limit which could be used in the diagnosis of subclinical vitamin D deficiency. (AU)

Effect of malnutrition on activity of two enzymes concerned with aminoacid metabolism in human liver

Aminoacid-activating enzymes and argininosuccinase were measured in liver-biopsy samples from twenty-two malnourished and recovering Jamaican infants. Aminoacid-activating-enzyme levels were increased initially and fell on recovery; argininosuccinase activity was low initially and rose on recovery. It is suggested that these changes are part of the adaptation which takes place in aminoacid metabolism in the malnourished state. (AU)

The measurement of total lysine turnover in the rat by intravenous infusion of L-[U-14C] lysine

Rats were infused intravenously for periods up to 7 hr with L-[U-14C]lysine. After about 4 hr the specific activity of free lysine in the blood reached a plateau. From the value of the plateau specific activity it is possible to calculate the total lysine flux into or out of the blood stream. In normal rats the flux is equivalent to a total protein turnover of 25-30 g kg-1 day-1. In male, but not in female rats the total flux decreased significantly with increasing body weight or age. Six weeks of protein depletion caused a decrease of 30 percent in the flux. Alloxan diabetes in a small number of rats caused no significant change. After the first « hr of the infusion the specific activity of the mixed serum proteins increased almost linearly. From the rate of increase and the specific activity of the free lysine at plateau, an approximate estimate can be made of the renewal rate of the serum proteins. This estimate must be too low, because the specific activity of the free amino acid at the site of synthesis, e.g. in the liver cell, must always be lower than in serum. The validity of the continuous infusion method is discussed in relation to other methods of measuring total amino acid or protein turnover.(AU)

Observations on the mechanisms of adaptation to the low protein intakes

Experiments are described which attempt to throw light on the mechanism by which animals and man can adapt to low protein intakes. In the rat, studies by constant infusion of labelled amino acid have shown that in the protein depleted animal there is a small reduction in the total protein turnover: this, however, is not enough to account for the great reduction in urinary nitrogen output. Constant infusion and single injection experiments agree in showing that in rats on a low protein diet there is a change in the pattern of protein turnover: synthesis of carcass protein (muscle and skin) is reduced, while that of liver protein is well maintained. The preservation of synthesis in liver seems to depend partly on increased re-utilization of amino acids liberated by the catabolism of tissue protein. This economy may be brought about by adaptive enzyme changes -decreased activity of the urea cycle enzymes and increased activity of amino acid activating enzymes in the liver. These changes, previously described by others in the rat have been shown to occur in the human liver also. Studies in human infant with 75selenium-labelled methionine provide some support for the concept that when the protein intake is limited, turnover is preferentially maintained in the liver. However, not all liver-produced proteins behave in the same way; studies of albumin kinetics in infants show that when the protein intake is altered, there is a rapid change in the rate of albumine synthesis, together with a redistribution of albumin between intra and extravascular spaces. Later and more slowly occurs a change, presumably compensatory, in the rate of albumin catabolism. Hormonal changes may play a part in these adjustments. Increased cortisone and decreased insulin activity would have the effect of promoting amini acid uptake at the expense of muscle. It is concluded that the net nitrogen loss which occurs when the protein intake is reduced results simply from the time-lag before the adaptive mechanisms come into play, and therefore cannot logically be regarded as the loss of reserve protein. The practical implications of this concept are discussed (Summary)

The micro-measurement of lysine in the Cartesian diver

0.5-1.0ul. of solution containing lysine is mixed in silicone-coated divers (Waterlow & Borrow, 1949) with 2 ul. of a suspension of L-lysine decarbolylase (Sigma Chemical Co.). Evolution of CO2 is complete after 1 hr. By this method it is possible to estimate 0.01 uM lysine with an accuracy of about 5 percent. The method has been applied to the measurement of the turnover rate of free lysine in the rat during constant intravenous infusion with 14C-lysine. Serial blood samples are taken from the tail to give 100 ul. of plasma. After deproteinazation with picric acid the free amino acid extract is evaporated to dryness and taken up in 5 ul. of acetate buffer pH 5. This provides enough material for two duplicate measurements of lysine content and for measurement of radioactivity (AU)

Further observations of enzymes in the human liver in malnutrition

In malnourished liver, although simple enzyme systems are on the whole well maintained, more complex functions may be damaged. These functions are of obvious importance for the vitality of the cell. It is necessary first to confirm these findings, and then to study the mechanism. Decreased phosphatide formation might impair the integrity of the mitochondrial membrane, but so far the type of test that we have used has not confirmed this(AU)