Biochemical medicine最新文献

Most of the previous studies on the effects of iron deficiency on skeletal muscle respiratory capacity and work performance have been investigated in severe or moderate iron-deficiency anemia. We report here that even in mild iron deficiency where the hemoglobin concentration was 10 g/dl and the iron stores in livers and spleen were not completely depleted, a marked reduction in succinate dehydrogenase was observed in skeletal muscles but not in heart. Similarly, cytochrome oxidase activities were reduced. Although no significant change in glycerophosphate dehydrogenase was detected in the iron-deficient rats, exposure to cold in this group greatly reduced this enzyme activity. As cold acclimatization accelerates marrow erythropoiesis (20) which in turn, demands more iron, it seems that in the iron-insufficient state, this iron demand for marrow activity may persist at the expense of the tissue iron pool, resulting in a marked reduction in glycerophosphate dehydrogenase activities. Since succinate dehydrogenase plays a significant role in the impairment of mitochondrial function and early fatigue of iron-deficient muscle (11), the present study shows that even in mild iron deficiency, some loss of muscle functions could result as succinate dehydrogenase activities were greatly reduced.

In order to elucidate the effects of aging on insulin content in human pancreas, the immunoelectrophoretic analysis of insulin was applied. The pancreas of senile humans appears to contain less total immunoreactive insulin, because of the decrement of proinsulin fraction after overnight fasting. The results suggest the involvement of insulin biosynthesis according to the aging process.

Aminopeptidase from dysgerminoma was purified and characterized using l-leucine-β-naphthylamide as substrate. The enzyme was resistant to puromycine, methionine, amastatin, bastatin, and EDTA, and it was heat labile at 60°C. The enzyme showed the same electrophoretic mobility as pregnant-patient serum oxytocinase CAP₁ on polyacrylamide gel electrophoresis. K_m value against S-benzylcysteine-p-nitroanilide was 4.2 × 10⁻⁴m. Oxytocin and vasopressin competitively inhibited the enzyme activity. Molecular weight of the enzyme was estimated to be 80,000 by Sephadex G-200 column chromatography. These results suggest that aminopeptidase from dysgerminoma is an oxytocinase-like enzyme, a placenta-specific protein.

Sixty-three studies in healthy normal volunteers (n = 29), malnourished cancer (n = 8) or non-cancer patients (n = 9), and postoperative radical cystectomy patients (n = 17) were conducted to evaluate the primed constant infusion labeling technique for the estimation of whole-body protein turnover under a variety of dietary conditions. [¹⁵N]Glycine was used as the tracer with a prime to infusion ratio of 1300 to 3300 min and a continuous-infusion rate of 0.11 to 0.33 μg ¹⁵N · kg⁻¹ · min⁻¹ for 24 to 36 hr. The isotopic steady-state enrichment was reached in all subjects both in urinary urea and ammonia between 10 and 26 hr (mean 18 ± 2). During protein calorie fasting the attainment of isotopic steady state is much quicker (10 to 18 hr) with a primed constant infusion than with a constant infusion alone (≈38 hr). A $\text{P}\text{I}$ ratio greater or less than 1800 (min) usually resulted in a delay of plateau attainment without affecting the protein turnover values. Reliable estimates of protein kinetics in humans can be made in clinical conditions with a 26-hr infusion of glycine at the rate of 0.28 μg ¹⁵N · kg⁻¹ · min⁻¹ with a $\text{P}\text{I}$ ratio of 1800 min, collecting six urine samples every 2 hr from 16 hr and analyzing for both urinary urea and ammonia enrichments.

Bilirubin accumulates within, and induces loose coupling in, rat liver mitochondria. This state, characterized by a normal protonmotive force, but increased oxygen consumption and inner membrane conductance, could impair cellular energy metabolism. Loose coupling is observed at bilirubin concentrations (12–24 μm) attained in tissues of kernicteric animals.

Condensed tannins isolated from cotton bracts are potent platelet agonists. They promote the secretion of 5-hydroxytryptamine from washed bovine platelets with an EC₅₀ of 35 μg/ml. However, when platelet-rich plasma was used in lieu of washed platelets, the potency of tannin was decreased over 50-fold. Reconstitution experiments demonstrated that some component in the plasma was responsible for the diminished potency of tannin. Fractionation of platelet-poor plasma suggested that albumin may be the inhibitory plasma component. Confirmation of this hypothesis was obtained from the finding that purified serum albumin at physiologic concentrations inhibited the tannin-mediated release of platelet 5-HT by more than 70%. These data suggest that any activation of platelets which may occur in vivo by the tannins present in inhaled cotton dust would require higher tannin concentrations than would have been predicted from our previous studies using washed platelets.

Untransformed diploid skin fibroblasts from eight normal adults, aged 24 to 74 years, catabolized several ¹⁴C-labeled substrates less effectively than cells from ten normal male infants. ¹⁴C-labeled substrate metabolism was quantitated either by measuring the evolution of ¹⁴CO₂ from the ¹⁴C-labeled compounds or the incorporation of ¹⁴C into cellular protein via transamination of tricarboxylic acid cycle intermediates derived from the ¹⁴C-labeled substrates. With these methods, adult cells catabolized [1-¹⁴C]butyrate, [1-¹⁴C]octanoate, and 1-[2-¹⁴C]leucine at rates 44 to 64% of those found in infant cells. The oxidation of [1,4-¹⁴C]succinate and [U-¹⁴C]malate was identical in both infant and adult cells, while [2,3-¹⁴C]succinate catabolism was mildly decreased in adult cells (65–80% of control). These observations parallel those made in rat tissues and confirm that the same phenomenon occurs in cultured human fibroblasts.

Human skeletal muscle acylphosphatase was purified by immunoaffinity chromatography using anti-horse muscle acylphosphatase antibodies. The three forms of the enzyme present in human muscle are very similar to those found in muscles of other animal species. The two main forms, Hu 1 and Hu 3, were also characterized with respect to molecular weight and some kinetic properties. Levels of acylphosphatase activity were measured in specimens of muscle from normals and from patients with various forms of muscular dystrophies and other myopathies. Acylphosphatase activity appears to be lower in all myopathic forms considered than in controls, and seems to be correlated with percentage of Ca²⁺ activation of (Ca²⁺ + Mg²⁺)-ATPase.

Riboflavin binding by plasma proteins from healthy human subjects was examined by equilibrium dialysis using a physiological concentration of [2-¹⁴C]riboflavin (0.04 μm). Binding ranged from 0.080 to 0.917 pmole of riboflavin/mg of protein (with a mean ± SD of 0.274 ± 0.206), which corresponded to 4.14 to 49.4 pmole/ml of plasma (15.5 ± 11.0) (N = 34). Males and females yielded similar results. Upon fractionation of plasma by gel filtration, the major riboflavin-binding components eluted with albumin and γ-globulins. Albumin was purified and found to bind riboflavin only very weakly (K_d = 3.8 to 10.4 mm), although FMN and photochemical degradation products (e.g., lumiflavine and lumichrome) were more tightly bound. Binding in the γ-globulin fraction was attributed to IgG and IgA because the binding protein(s) and immunoglobulins copurified using various methods were removed by treatment of plasma with protein A-agarose, and were coincident upon immunoelectrophoresis followed by autoradiography to detect [2-¹⁴C]riboflavin. Differences among the plasma samples correlated with the binding recovered with the immunoglobulins. Binding was not directly related to the total IgG or IgA levels of subjects. Hence, it appears that the binding is due to a subfraction of these proteins. These findings suggest that riboflavin-binding immunoglobulins are a major cause of variations in riboflavin binding in human circulation, and may therefore affect the utilization of this micronutrient.

The amino acid contents of tumor cells that are either sensitive or resistant to treatment with l-asparaginase were measured. These amino acid concentrations were measured as a function of incubation time with l-asparaginase or as a function of the l-asparaginase dose. The cell types compared were the mouse leukemia lines L5178Y (sensitive to l-asparaginase treatment) and L5178Y/l-ASE (resistant to l-asparaginase treatment). Upon l-asparaginase treatment both cell lines lost most of their cellular asparagine but, whereas the resistant cells exhibited the ability to rebound to about 50% of initial values, the sensitive cells did not. While previous work had suggested that asparagine-dependent glycine synthesis was essential for sensitive cells (but not in resistant cells), we found no difference in the glycine content of either of the two cell lines as a function of either time or dose that would support this hypothesis. Major differences between the two cell lines were seen in the content of the essential amino acids before treatment with l-asparaginase. After incubation without l-asparaginase the contents of the two cell lines became similar. These results are discussed in terms of possible mechanisms of l-asparaginase sensitivity and resistance.