Efficacy of phase-feeding in supporting growth performance of broiler chicks during the starter and finisher phases.

A feeding regimen has been developed that uses regression equations to predict amino acid requirements over time. Phase-feeding (PF) of broilers was tested to evaluate its efficacy compared with feeding broilers NRC or Illinois ideal chick protein (IICP) recommendations. In Experiment 1, NRC or IICP requirements for lysine, sulfur amino acids, and threonine were fed from 0 to 21 d, whereas PF was tested using a series of three diets (0 to 7, 7 to 14, and 14 to 21 d). No differences (P > 0.05) in weight gain, feed intake, feed efficiency, digestible amino acid intake, or gain per unit digestible amino acid intake were noted among chicks fed NRC, IICP, or PF diets. In Experiment 2, NRC or IICP requirements were fed from 40 to 61 d, whereas PF was tested using a series of three diets (40 to 47, 47 to 54, and 54 to 61 d). No differences (P > 0.05) in weight gain or feed intake were observed, but the feed efficiency of birds fed the IICP diet was decreased (P < 0.05). The IICP and PF diets resulted in decreased (P < 0.05) digestible lysine and threonine intake; gain per unit digestible lysine and threonine intake was increased (P < 0.05) by PF. No differences (P < 0.05) in breast meat, wing, or leg yield were noted among treatments. Economic analysis indicated that PF may facilitate reduced dietary costs without sacrificing growth performance or carcass yield.

Modification of sulfhydryl groups of creatine kinase by urate.

The catalytic activity of rabbit skeletal muscle creatine kinase is diminished in solutions of sodium urate. The rate of inactivation follows first-order kinetics and is dependent upon urate concentrations. During the course of inactivation, only partial reactivation can be obtained by exposure to thiol agents. Reduction in the number of reactive sulfhydryl groups from eight per dimer to four accompanies inactivation of the enzyme, but no alteration in electrophoretic mobility is detectable.

Defluorination of methoxyflurane by a glutathione-dependent enzyme.

Partial purification from rat liver of an enzyme which catalyzes defluorination of methoxyflurane is described. Fractionation of liver homogenates by protamine sulfate and ammonium sulfate precipitation and by Sephadex G-100 chromatography results in a 10-fold purification with 53% recovery. The enzyme requires glutathione for activity, and other sulfhydrhyl compounds cannot be substituted. The enzyme appears to be a glutathione S-transferase, possibly one of several which have recently been characterized.

Creatine kinase activity in serum and uric acid solution.

Skeletal muscle creatine kinases from man and rabbit, activated to measured specific activities by thiol agents, were inactivated in human serum and in uric acid solution, and the extent of their subsequent reactivation by dithiothreitol was determined. Both enzymes were completely reactivated from uric acid solution but were only 60-70% reactivated from serum. No inactivation occurred within 14 days if serum samples contained dithiothreitol (0.01 M) and were stored at -17 degrees C.

Identification of a creatine kinase inhibitor in human serum.

Human skeletal muscle creatine kinase is inhibited by a dialyzable factor in human serum. The inhibitor was fractionated from other serum components by ultrafiltration and chromatography on Sephadex G-10 and was identified as uric acid by spectral, chromatographic, and kinetic methods. Its quantitative kinetic properties are identical to those of uric acid, both as a substrate for uricase and as an inhibitor of creatine kinase. Inhibition of creatine kinase by the natural inhibitor and by known uric acid is completely reversible by addition of thiol compounds.