Pauwels S, Najdovski T, Dimaline R, Lee C M, Deschodt-Lanckman M
Department of Nuclear Medicine, University of Louvain, Brussels, Belgium.
Biochim Biophys Acta. 1989 Jun 13;996(1-2):82-8. doi: 10.1016/0167-4838(89)90098-8.
The degradation of human sulphated heptadecapeptide gastrin (G17s) by human endopeptidase 24.11 was studied in vitro. The products of degradation were characterized by HPLC, region-specific gastrin radioimmunoassay and amino acid analysis. The enzyme cleaved G17s at four sites, Trp4-Leu5, Ala11-Tyr12, Gly13-Trp14 and Asp16-Phe17. The patterns of fragments produced when sulphated and unsulphated G17s are hydrolysed by endopeptidase 24.11 indicate that the enzyme cleaves both substrates at the same four bonds. However, the sulphated G17 was 3-times less rapidly degraded than the unsulphated G17 (G17ns). In contrast, the rate of cleavage of the octapeptide cholecystokinin (CCK8) was faster when the peptide was sulphated. The kinetic data of endopeptidase 24.11 indicated similar Km values for sulphated or unsulphated gastrin and CCK; sulphated CCK8 exhibited a 2-fold higher kcat/Km value compared to unsulphated CCK8, whereas G17s exhibited a 2-fold lower kcat/Km value compared to G17ns. The results indicate that the presence of a sulphate group causes a marked reduction in the rate of hydrolysis of gastrin by endopeptidase 24.11, whereas sulphation enhances cholecystokinin degradation by the same enzyme. They also suggest that endopeptidase 24.11 may be responsible for the difference in metabolism of sulphated and unsulphated G17, previously observed in human circulation.
在体外研究了人内肽酶24.11对人硫酸化十七肽胃泌素（G17s）的降解作用。通过高效液相色谱法、区域特异性胃泌素放射免疫测定法和氨基酸分析对降解产物进行了表征。该酶在四个位点切割G17s，即Trp4-Leu5、Ala11-Tyr12、Gly13-Trp14和Asp16-Phe17。当硫酸化和未硫酸化的G17s被内肽酶24.11水解时产生的片段模式表明，该酶在相同的四个键处切割两种底物。然而，硫酸化的G17降解速度比未硫酸化的G17（G17ns）慢3倍。相反，当八肽胆囊收缩素（CCK8）硫酸化时，其切割速度更快。内肽酶24.11的动力学数据表明，硫酸化或未硫酸化的胃泌素和CCK的Km值相似；硫酸化的CCK8与未硫酸化的CCK8相比，kcat/Km值高2倍，而G17s与G17ns相比，kcat/Km值低2倍。结果表明，硫酸根的存在导致内肽酶24.11对胃泌素的水解速率显著降低，而硫酸化则增强了同一酶对胆囊收缩素的降解。它们还表明，内肽酶24.11可能是先前在人体循环中观察到的硫酸化和未硫酸化G17代谢差异的原因。
