Étude du transfert enzymatique de D‐[¹⁴C]mannose á partir de GDP‐[¹⁴C]mannose, sur un accepteur endogène dans les microsomes d'<i>Aspergillus niger</i>

Abstract

A glycoprotein‐mannosyltransferase, utilsing an endogenous acceptor found in Aspergillus niger is herein characterized. Data presented indicate that among the subcellulr fractions, only microsomers are active in the mannose transfer reactions. The enzyme catalising the transfer requires Mn ++ or Mg ++ (1–2 mM) and has an optimum pH of 6.8 and an optimum temperature of 22°. It exibits a K m of 0.2 μM for GDP‐mannose. The transfer is inhibited by ATP, CTP and also bt GTP or its structural analogue β‐γ‐methlene‐guanosine triphosphate, but AMP or GDP have only a slight inhibitory action. Triton X‐100 causes of 2‐ to 3‐fold enhancement of incorporation of mannose when a suitable detergent: protein ratio is applied. The efficiency of this enzyme‐aceptor system is discussed.