Comparison of the steroidogenic and melanotropic activities of corticotropin, alpha-melanotropin and analogs with their lipolytic activities in rat and rabbit adipocytes.

The ability of alpha-melanotropin and a series of synthetic peptides related to adrenocorticotropin (ACTH) to stimulate steroidogenesis in isolated rat adrenal cells, melanin dispersion in frog melanophores and lipolysis in rat and rabbit fat cells have been studied. It was found that the steroidogenic activity closely paralleled the lipolytic activity of these peptides in rat fat cells, whereas the melanocyte stimulating activity paralleled the lipolytic activity in rabbit fat cells. These results indicate that the structural requirements for stimulating steroidogenesis in isolated rat adrenal cells and lipolysis in isolated rat fat cells are quite similar. The structural features required for eliciting lipolysis in rabbit fat cells appear to be very similar to those necessary for stimulating frog melanophores. The possibility that regulation of lipid metabolism in the rabbit may be a new function acquired by melanotropin is discussed.     

The structure of monellin and its relation to the sweetness of the protein.

The sweet protein monellin [1-3] has been shown to consist of two non-identical subunits of 50 and 42 amino acid residues, which were separated electrophoretically and chromatographically. Automatic sequential Edman degradation gave the complete sequence of the longer subunit, and a partial sequency of the shorter one. It was found that the sweetness of monellin requires the undissociated molecule. The individual subunits were not sweet, neither did they block the sweet sensation of sucrose or monellin. Blocking of the single SH of monellin abolished its sweetness as did reaction of the single methionyl residue with CNBr. Since the cysteinyl and methionyl residues appear to be adjacent, it is suggested that this part of the molecule is essential for its sweetness.     

Amino-terminal sequences of indoleglycerol phosphate synthetase of Escherichia coli and Salmonella typhimurium.

The partial sequences of the first 40 residues of indoleglycerol phosphate synthetase of Escherichia coli and Salmonella typhimurium were determined, and three amino acid differences were observed among the 38 residues compared.     

Tracer flow,permeability, and partial conductance

Summary It is often not possible to evaluate a permeability coefficient for net flowP from the small flows produced by physiological gradients of concentration or electrical potential. The common use of a tracer permeability coefficientP ^x for this purpose, under the assumption thatP ^x =P, requires that the species be transported passively, and that there be no significant coupling between its flow and that of other chemical species, and between the flows of its tracer and abundant isotopes (isotope interaction). These conditions are often not satisfied. However, for passive transport in the absence of coupling of flows of different chemical species the measurement of tracer flow at two values of electrical potential difference evaluates (P ^x /P) and thusP. In the presence of coupling of flows of different chemical species, although these measurements no longer evaluateP, they evaluate the partial conductanceG. A graphical method of evaluating (P ^x /P),P andG is presented.     

Phosphoprotein phosphatase-catalyzed dephosphorylation of the 22,000 dalton phosphoprotein of cardiac sarcoplasmic reticulum.

The present study demonstrated the presence within the myocardium of phosphoprotein phosphatase activity which can account for dephosphorylation of a 22,000 dalton phosphoprotein of cardiac sarcoplasmic reticulum that has been associated with the stimulatory effects of adenosine 3':5'-monophosphate (cyclic AMP)-dependent protein kinase on calcium transport (Tada, M., Kirchberger, M. A., and Katz, A. M. (1975) J. Biol. Chem. 250:2640-2647). Dog cardiac microsomes, consisting mainly of fragmented sarcomplasmic reticulum, were phosphorylated by incubation with cyclic AMP-dependent protein kinase and [gamma-32P]ATP, and subsequently washed with trichloroacetic acid or buffered KCl. Phosphorylated microsomes contained approximately 1 nmole of 32P bound per mg of microsomal protein, 32P labeling occurring almost exclusively at the 22,000 dalton component. Soluble phosphoprotein phosphatases, isolated from the cytosol, catalyzed dephosphorylation of 32P-labeled microsomes. The existence of a phosphoprotein phosphatase that is associated with the microsomes was demonstrated by the ability of the microsomes to dephosphorylate 32P-histone. This membrane-associated phosphatase activity can also account for a rapid decrease in the amount of 32P-labeling of the 22,000 dalton protein. The dephosphorylation of the phosphorylated 22,000 dalton protein by phosphoprotein phosphatase satisfies an important requirement for the phosphorylation of the 22,000 dalton protein to serve a physiological role, namely, its reversibility.     

Genetics of acheiropodia (the handless and footless families of Brazil). VII. Population dynamics.

Since carriers of the acheiropodia gene cannot be distinguished from noncarriers, parents and normal sibs of affected individuals have been used to estimate the fitness of heterozygotes. No significant difference in biologic fitness (viability and fertility) between normal sibs and the general population could be detected. A comparison between acheiropods and their normal sibs showed the following: (1) a nonsignificant difference in stillbirth rate; (2) a higher mortality rate of acheiropods in the first 5 years of life; (3) a relative viability not larger than .7; (4) a relative fertility no greater than .14, due to "cosmetic effects"; and (5) a fitness of .10 or lower. The total number of acheiropodia genes in Brazil has been calculated as 25,000 in the 1970s. The data are compatible with an extremely low mutation rate and a very stable locus. It is suggested that all Brazilian acheiropods can be traced to a single mutation. A conservative estimate of the number of acheiropods to appear in the future in Brazil is 14,000 with an extinction time of no less than 2,300 generations or almost 70,000 years. A variety of other parameters have been calculated.     

高、低氮浓度对2株真眼点藻的生长和油脂积累的影响

【目的】研究氮浓度对真眼点藻纲(Eustigmatophyceae)的2株高产油微藻大真眼点藻(Eustigmatos magnus,EM)和波氏真眼点藻(Eustigmatos polyphem,EP)的细胞形态、生长、总脂含量、脂质组成和脂肪酸组成与含量的时序变化规律。【方法】利用高氮(18.0 mmol/L NO3?-N)和低氮(3.6 mmol/L NO3?-N)浓度培养微藻。【结果】形态观察结果表明,大真眼点藻(E. magnus)和波氏真眼点藻(E. polyphem)营养细胞具有1个周生的裂叶状叶绿体,细胞质中有液泡,内含能够振动的颗粒物,以及一个较为明显的红色色素体;生殖方式通过形成2个D形或4个四角形的似亲孢子;随着培养周期的延伸和营养盐的消耗,细胞中油体逐步形成,其数量不断增加,体积不断增大。实验结果表明,初始氮浓度对2种微藻的总脂积累及生长均有显著影响(P<0.05),低氮浓度下2种微藻的生物质浓度分别为9.0 g/L和8.5 g/L,均低于高氮浓度下的生物质浓度。而低氮浓度下2种微藻的总脂、中性脂和总脂肪酸的含量以及总脂、中性脂与总脂肪酸的单位体积产率均明显高于高氮浓度组,其最高值分别为：59.10%、51.90%、46.95%和0.28、0.24、0.22 g/(L·d) (EM);64.20%、56.80%、50.01%和0.32、0.28、0.25 g/(L·d) (EP)。脂肪酸分析结果表明,两种微藻的脂肪酸主要成分均为棕榈酸(C16:0)、棕榈油酸(C16:1)、油酸(C18:1)和二十碳五烯酸(C20:5,EPA),四者的总含量(占总脂肪酸)分别达到85.83%和85.48%,其中棕榈油酸的含量最高。【结论】低氮浓度胁迫有利于大真眼点藻和波氏真眼点藻细胞内油脂的积累,两种微藻均为适合于生产生物柴油的油脂生产藻株。     

乳粉中嗜热菌污染研究进展

嗜热菌是乳粉中的常见污染菌,是影响乳粉品质的一个重要因素。本文综述乳粉中嗜热菌的种类、污染源对乳品工业的危害及其控制手段的研究进展,为国内相关领域研究提供参考。