Arginine residues replacement

The bcny.odiazepinc recognition. site is in the extracellular N terminus of the ai. aj, of), and subunits. GABA receptors with or subunits do not respond to benzodiazepines. 04 and Of, subunits have an arginine residue replacing histidine at position 101 of the extracellular N-terminal domain O) subunits are required fur sedative and hypnotic effects, and to a lesser extent, anticonvulsant effects of ben-ro(liazcpinc.s subunits are required for the anxiolytic ef-... 

Fig. 12. Tryptic map of it-PA (mol wt = 66,000) showing peptides formed from hydrolysis of reduced, alkylated rt-PA. Separation by reversed-phase octadecyl (C g) column using aqueous acetonitrile with an added acidic agent to the mobile phase. Arrows show the difference between A, normal, and B, mutant rt-PA where the glutamic acid residue, D, has replaced the normal arginine residue, C, at position 275.

Histones are small, basic proteins required to condense DNA into chromatin. They have been first described and named in 1884 by Albrecht Kossel. There are five main histones HI, H2A, H2B, H3 andH4. An octamer of core histones H2A, H2B, H3 andH4 is located inside a nucleosome, the central building block of chromatin, with about 150 base pairs of DNA wrapped around. The basic nature of histones, mediated by the high content of lysine and arginine residues, allows a direct interaction with the acidic phosphate back bone of DNA. The fifth histone HI is located outside at the junction between nucleosomes and is referred to as the linker histone. Besides the main histones, so-called histone variants are known, which replace core histones in certain locations like centromers. 

Oxytocin, a peptide which initiates uterine contractions during labour is identical in structure to ADH except at position 8 where a leucine residue replaces arginine. The close structural similarity but radically different biological functions, illustrate how specific some hormone receptors are in recognising only their own signal . 

Isolation of alkaline phosphatase from Escherichia coli in which 85% of the proline residues were replaced by 3,4-dehydro-proline affected the heat lability and ultraviolet spectrum of the protein but the important criteria of catalytic function such as the and were unaltered (12). Massive replacement of methionine by selenomethionine in the 0-galactosidase of E. coli also failed to influence the catalytic activity. Canavanine facilely replaced arginine in the alkaline phosphatase of this bacterium at least 13 and perhaps 20 to 22 arginyl residues were substituted. This replacement by canavanine caused subunit accumulation since the altered subunits did not dimerize to yield the active enzyme (21). Nevertheless, these workers stated "There was also formed, however, a significant amount of enzymatically active protein in which most arginine residues had been replaced by canavanine." An earlier study in which either 7-azatryptophan or tryptazan replaced tryptophan resulted in active protein comparable to the native enzyme (14). 

Replacement of amino acid residues in a polypeptide chain still is achieved most easily by isolating mutant proteins from bacteria, but Laskowski, Jr. and his colleagues at Purdue University have developed a method for enzymatically removing an essential arginine residue from the reactive site of soybean trypsin inhibitor (Kunitz) and replacing it with a lysine residue (84). 

Their gene mutation causes the histidine residue in this position to be replaced by an arginine residue. The side chain of arginine is... 

Replacement of Cys-430 of the E. coH W aspartase gene with a tryptophan residue has been shown to enhance aspartase activity threefold at pH 6.0, but only slightly at pH 8, the optimum for the wild-type enzyme [40]. Limited proteolysis of the mutated protein completely inactivates the enzyme, showing that truncation activation and the Cys-430 mutation are not additive. Substitution of Lys-126 to an arginine residue of the E. coH AS. 881 aspartase causes a fivefold enhancement in specific activity at pH 8.5 with a concomitant increase in the thermostability... 

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