Histidine metabolism in experimental protein malnutrition in rats

1. The activities of the enzymes histidase, urocanase and histidine-pyruvate transaminase were studied in rats under conditions of protein malnutrition. Urocanase and histidase activities in liver were markedly lowered in experimental protein malnutrition, but the activity of histidine-pyruvate transaminase was unaffected. There is a metabolic control in vivo of the enzymes involved in the catabolism of histidine. 2. Significant changes in the urinary excretion of histidine, composition of liver and serum were apparent in the protein-malnourished rat. 3. The changes in the activities of the enzymes and other parameters were of a reversible nature and dependent on the nature of the dietary protein. 4. The significance of these findings is discussed in relation to abnormal histidine metabolism in kwashiorkor.

Hepatic pyridine nucleotides content in rat--a better indicator for determining available niacin values of food

After 10 days depletion period with niacin free diet, weanling rats were repleted with either reference diets containing niacin at four levels (2, 4, 8 and 12 mg/kg diet) or test diets containing test material at two levels as source of niacin. Gains in body weight and hepatic pyridine nucleotides content increased with increase in niacin intake. The correlation coefficient for hepatic pyridine nucleotides content and niacin intake was 0.98, whereas for weight gain and niacin intake was 0.89. Dried skim milk and pearl millet were taken as test materials. Dried skim milk with most of its niacin in free form showed 98% niacin equivalent to be bioavailable whereas in pearl millet niacin was in bound form and bioavailability equivalent was only 48 per cent.

Influence of milk factors on riboflavin uptake by rat intestinal everted sac

The uptake of riboflavin was measured in Krebs' medium and a system consisting of riboflavin-free dialyzed milk (providing milk factors) equalized to Krebs' medium with respect to different salt concentration and pH. The final riboflavin concentration in the medium ranged between 0.1 and 0.5 microM. Total riboflavin incorporation was greater in the milk system and the increase ranged between 120 and 134% in comparison with Krebs' medium (100%). The Michaelis-Menten constant (Km) and Vmax for labelled riboflavin uptake were calculated by Lineweaver-Burk plotting of data. Km value decreased from 1.23 microM for Krebs' medium to 0.75 microM in the presence of milk factor(s). Vmax values were 62 and 60 pmol/100 mg tissue/min for Krebs' and milk systems, respectively. It was concluded that milk factor(s) enhanced intestinal uptake of riboflavin.

The effect of the digestion products of lactose (glucose and galactose) on its intraintestinal, in vivo hydrolysis by exogenous microbial beta-D-galactosidase

Exogenous, microbial beta-D-galactosidases are capable of effecting hydrolysis of lactose in situ in the gastrointestinal tract of lactase-deficient subjects when given as replacement therapy at mealtime. As its digestion products-glucose and galactose-are known to inhibit lactose hydrolysis in vitro, the effect of adding excess monosaccharide to milk on the hydrolytic efficiency of a beta-galactosidase from Aspergillus niger in adult lactose-malabsorbers was tested. Subjects were studied with 360-ml volumes of milk containing 18 g of carbohydrate. This was administered as intact milk, as lactose-prehydrolyzed milk, and as milk to which 399 mg of Lactase N was added within 5 minutes of consumption. This latter Lactase N-treated milk was administered alone and with graded levels of glucose-9, 18, and 36 g-and with similar doses of galactose. The Lactase N enzyme alone at mealtime reduced breath H2 production by 68% as compared to intact milk. The addition of monosaccharides produced no change in the apparent hydrolytic efficiency of the Lactase N in situ. Thus, product inhibition is unlikely to be the basis for the limited efficiency of intraintestinal hydrolysis of milk lactose by the enzyme from A niger.