Further studies of the role of Ser-16 in the regulation of the activity of phenylalanine hydroxylase.

It was previously proposed that the activation of rat liver phenylalanine hydroxylase (EC 1.14.16.1) by cAMP-dependent protein kinase-mediated phosphorylation of Ser-16 is due to the introduction of the negatively charged phosphate group. To explore the validity of this proposal, we have applied site-directed mutagenesis to specifically replace Ser-16 with negatively charged amino acids, glutamic and aspartic; with polar uncharged amino acids, asparagine and glutamine; with the positively charged amino acid lysine; and with the nonpolar hydrophobic amino acid alanine. The wild-type and mutant enzymes were purified to homogeneity, and the importance of Ser-16 in the activation of phenylalanine hydroxylase was examined by comparing the state of activation of the phosphorylated form of the wild-type hydroxylase with that of the mutants. The kinetic studies carried out on the wild-type phosphorylated hydroxylase showed that all the activation could be accounted for by an increase in Vmax with no change in Km for either phenylalanine or the pterin cofactor. Replacement of Ser-16 with a negatively charged residue, glutamate of aspartate, resulted in the activation of the hydroxylase by 2- to 4-fold, whereas replacement with glutamine, asparagine, lysine, or alanine resulted in a much more modest increase. Further, lysolecithin was found to stimulate the phosphorylated hydroxylase and the mutant enzymes S16E and S16D by a factor of 6-7. In contrast, the mutants S16Q, S16N, and S16A all showed the same magnitude of activation as the wild-type with lysolecithin. Therefore, this study demonstrates that activation of the enzyme by phosphorylation of Ser-16 by cAMP-dependent protein kinase is due to the introduction of negative charge(s) and strongly suggests the involvement of electrostatic interaction between the regulatory and catalytic domains of the hydroxylase.     

次侧切术治疗期肛裂前后肛门直肠压力对比分析

目的 :探讨次侧切开内括约肌治疗肛裂术前、术后肛门直肌压力的变化。方法 :采用自行设计的次侧方内括约肌切开加双缘结扎术治疗 期肛裂 6 0例 ,测定手术前后肛门直肠压力 ,并与 6 0例正常人肛压比较 ,评价新术式治疗 期肛裂的临床疗效及其对肛门功能的影响。结果 :显示术后患者肛管静息压显著降低 ,与术前比较有显著性差异 (P <0 .0 1) ,与正常人比较无显著性差异 (P>0 .0 5 ) ;肛管最大收缩压与术前及正常人比较无显著性差异 (P>0 .0 5 )。结论 :次侧方内括约肌切开加双缘结扎术能有效地解除内括约肌痉挛 ,从根本上消除高肛压 ,从而彻底治愈肛裂 ,而且不影响肛门功能。     

亮菌多糖抗小鼠辐射损伤作用的研究

目的观察亮菌多糖（ATS）对辐射损伤的保护作用。方法将小鼠随机分为空白对照组（0．9％生理盐水）、辐射模型组、阳性对照组（参芪片）和ATS多糖不同剂量实验组（80、160和320mg／kg）。以γ射线照射小鼠全身，引起辐射损伤后观察各组小鼠30d存活率、白细胞（WBC）数、精子畸变率、骨髓微核（MN）细胞数、骨髓DNA含量和免疫器官重量及血清和肝组织中的超氧化物歧化酶（SOD）和丙二醛（MDA）含量等。结果ATS能提高受照小鼠存活率（P〈0．05）及SOD活性（P〈0．05）、升高WBC数（P〈0．05）和骨髓DNA含量（P〈0．05），抑制小鼠精子畸变率（P〈0．05）和骨髓MN细胞数的增加（P〈0．05），并使受照小鼠胸腺、脾脏重量回升（P〈0．05），还能增加内源性脾结节数（P〈0．05），降低MDA含量。结论ATS对γ射线所致小鼠辐射损伤有较好的保护作用。