Substantial increase of protein stability by multiple disulphide bonds

Disulphide bonds can significantly stabilize the native structures of proteins. The effect is presumed to be due mainly to a decrease in the configurational chain entropy of the unfolded polypeptide. In phage T4 lysozyme, a disulphide-free enzyme, engineered disulphide mutants that crosslink residues 3-97, 9-164 and 21-142 are significantly more stable than the wild-type protein. To investigate the effect of multiple-disulphide bonds on protein stability, mutants were constructed in which two or three stabilizing disulphide bridges were combined in the same protein. Reversible thermal denaturation shows that the increase in melting temperature resulting from the individual disulphide bonds is approximately additive. The triple-disulphide variant unfolds at a temperature 23.4 degrees C higher than wild-type lysozyme. The results demonstrate that a combination of disulphide bonds, each of which contributes to stability, can achieve substantial overall improvement in the stability of a protein.     

美国学校数学课程演化的历史观(1900-2006)

通过对100多年来美国学校数学课程演化的分析与思考,旨在提供一种认识美国数学课程的历史观,并从中窥探美国数学课程演化的艰巨性、曲折性和发展性,以启示如何更有效地进行数学课程改革.     

Thyrotropin-releasing hormone does not inhibit lysine vasopressin-induced growth hormone secretion in normal men

Summary In order to establish whether thyrotropin-releasing hormone (TRH) inhibits lysine-vasopressin (LVP)-induced growth hormone (GH) release, six normal men were tested with LVP alone or in combination with TRH. LVP strikingly increased serum GH levels; this response was not altered by TRH. These results indicated that in man TRH is not involved in the control of GH secretion in response to LVP.     

Host tree unsuitability recognized by pine shoot beetles in flight

Summary In spring, the landing rate of flying European pine shoot beetles,Tomicus piniperda L., on injured Scots pine diminishes as colonization continues. This is due to olfactory cues that indicate progressive host degradation. Verbenone was shown to play a role in the beetle's recognition of this unsuitability of a formerly suitable host, since the compound was increasingly released from colonized tree sections as they aged, but not from uninfested sections. Also, the release of verbenone at natural rates in the forest inhibited the attraction of beetles to host monoterpenes.     

Rate of tryptophan hydroxylation in vivo in brain nuclei of genetically hypertensive rats of the Lyon strain

The rate of tryptophan hydroxylation in vivo is unaltered in brain areas of 5, 9 and 21 week-old Lyon genetically Hypertensive (LH) rats as compared to both Lyon Normotensive (LN) and Low Blood Pressure (LL) rats, except for a decrease in the C1 area of the medulla oblongata in 9 week-old animals.     

Modulation of single Ca2+-dependent K+-channel activity by protein phosphorylation

There is considerable evidence that cyclic AMP can modulate the electrical activity of excitable cells and that protein phosphorylation by the catalytic subunit (CS) of cAMP-dependent protein kinase is a necessary step in these modulatory effects. In analogy to alterations in enzyme activities following phosphorylation, it seems possible that direct phosphorylation of ion-channel proteins may alter their gating properties, giving rise to the observe changes in electrical activity. However, the results obtained so far do not indicate whether it is ion channels themselves that are phosphorylated, or whether phosphorylation is simply an early step in some cascade of events which leads ultimately to modulation of channel activity. The development of single-channel recording techniques has provided a way to investigate this question. Here we describe effects of CS on the activity of individual CA2+-dependent K+ channels from the nervous system of the land snail Helix measured in isolated membrane patches and in artificial phospholipid bilayers. The results demonstrate that cAMP-dependent protein phosphorylation produces long-lasting changes in the activity of individual channels, and indicate that the relevant phosphorylation site is closely associated with the channel.