W. Duane Brown

Catalysis of unsaturated lipid oxidation by iron protoporphyrin derivatives

Abstract Various derivatives of hemoglobin and myoglobin, including methemoglobin and metmyoglobin; imidazole hemoglobin hemichrome and imidazole myoglobin hemichrome; carbon monoxide hemoglobin; oxyhemoglobin; and nitric oxide hemoglobin were used as catalysts for unsaturated lipid oxidation. All were active catalysts, but there were induction periods with some of the ferrous forms. Experiments in which catalysts were extracted from oxidizing mixtures and examined spectrophotometrically indicated that the ferrous forms of the hematin compounds were converted to the ferric form at the time of extraction. Denatured methemoglobin and nitric oxide hemoglobin behaved similarly to the analogous native protein compounds.

γ-Irradiation of purified myoglobins: I. Effect on physicochemical properties☆

Abstract Solutions of purified sperm whale and yellowfin tuna myoglobins were subjected to γ-irradiation at levels of 0–500 krads in nitrogen atmospheres. Samples to be irradiated included, in most instances, individual fractions of the three myoglobins that can be isolated from both whale and tuna preparations free of other proteins. Irradiated myoglobins precipitated from solution as a function of dose and concentration; least precipitation occurred with concentrations between 7 and 10 mg per milliliter. All precipitates were insoluble in 6 M urea except for one whale fraction. The absorbancy of samples in the 280 mμ region increased considerably following irradiation; in some dilute solutions an absorption maximum appeared at about 240 mμ. Changes in absorbancy in the visible region suggest that oxymyoglobins are partially oxidized, and that metmyoglobins are converted to substances with spectra similar to oxymyoglobins. There was little change in sedimentation velocity of myoglobins as a result of irradiation. Deamination of the proteins was induced by irradiation, and there was splitting of small peptide fragments not yet identified. Electrophoretic behavior was altered by irradiation, with samples subjected to 500-krad levels not moving from the origin on cellulose acetate strips, except for one whale fraction. There was an apparent loss of the sulfhydryl group of tuna myoglobins that was proportional to radiation dose; however, dialysis of irradiated material prior to sulfhydryl assay increased the SH value. The SH group was without apparent effect on radiation susceptibility, since whale myoglobins, which have no SH groups, behaved similarly to tuna myoglobins in most cases.

Myosin from dystrophic and control chicken muscle: I. Preparation and preliminary characterization☆☆☆

Abstract Myosins have been isolated from superior pectoralis muscle of control and dystrophic chickens. Various extraction procedures were used, all followed by DEAES-ephadex chromatography. Myosins from either source showed the same chromatographic elution patterns (KCl-gradient in pyrophosphate buffer). Variation in ATPase activity was without regard to muscle type; values ranged from 4.7 to 7.0 units (μmoles P i /mg protein/5 minutes). Loss of activity on aging at 4 ° was similar for both types. Sedimentation coefficients for both types of myosin were determined over a wide concentration range. All values fitted a straight line plot of s 20, w versus concentration. Extrapolation to zero concentration showed s o 20, w values of 5.94 S for both myosins. Ultraviolet spectra of myosins from both sources coincided. All measurements suggest that myosins from control and dystrophic muscle are identical. However, there are substantial differences in extractability (i.e., yield) of myosin from the two types of muscle. About 25% as much crude myosin was obtained from dystrophic as from control muscle (wet weight basis; water content of both types about 75%).

Myoglobin in control and dystrophic chicken muscle

Abstract This study shows no differences in the character of myoglobin in muscles from control and genetically dystrophic chickens. Our data on cellulose chromatography, acrylamide gel electrophoresis, sedimentation velocities, spectra, isoelectric points, and amino acid analyses provide useful information on the first avian myoglobin to be added to the list of mammalian and fish myoglobins which have already been characterized.

Sulfhydryl content of tuna myoglobin.

Abstract A homogeneous preparation of myoglobin made from the red meat of yellowfin tuna ( Neothunnus macropterus ) resembled previously described myoglobins in solubility, absorption spectra, iron content, and sedimentation velocity, but, uniquely, contained one to two free sulfhydryl groups per assumed molecular weight of 16,000–17,000.

Myosin from dystrophic and control chicken muscle: II. Molecular weight, electrophoretic properties, salt sensitivity, aggregation, and amino acid composition☆

Abstract Myosins from muscle of control and genetically dystrophic chicken muscle have been isolated by conventional salt fractionation procedures and further purified by chromatography on DEAE-Sephadex. Purified myosins from both muscle sources appeared to have the same molecular weight (about 5.3 × 10 5 ) as determined by high-speed equilibrium centrifugation. They also exhibited similar electrophoretic behavior, with isoelectric points at pH 5.5. After incubation in 0.5 m KCl-0.01 m histidine (pH 6.8) at 26 ° for as long as 24 hours, some monomeric myosin remained. Incubation at 37 ° for 3 hours resulted in complete aggregation and loss of ATPase activity. Myosins from both muscle types were relatively stable at 0 ° for 30 days in the KCl-histidine buffer. The following solvent systems were equally satisfactory: tetramethylammonium chloride, histidine; tetraethylammonium chloride, histidine; and tetramethylammonium phosphate. ATPase activities of mysoins from either muscle type were similarly lowered by increasing concentrations of KCl. Amino acid compositions appeared to be the same. The present results, together with those from an earlier study, provide no evidence for any molecular alteration in myosin as a result of the dystrophic condition. In general, chicken myosin appears to retain enzyme activity better and be less subject to aggregation than myosin from rabbit and several species of fish.

Present Knowledge of Protein Nutrition, Part 2

Part 1 of this article, published last month, discussed various processes and factors involved in the transformation of dietary protein to tissue protein and considered some of the known nutritional effects on protein synthesis. Part 2 presents several approaches to the determination of both protein requirements and protein quality. Part 3 will be published next month.