[Cytidine monophosphatase (CMPase), a transport hydrolase of membrane-bound glycoconjugates]

Membrane bound glycoconjugates (glycoproteins, -lipids and proteoglycans) of the plasmalemmaa and of the cytoplasmic membrane tube system are responsible for essential cell function. Accordingly it is necessary to keep them in a proper functional state. Our results indicate a possible involvement of cytidine monophosphatase (CMPase) in these events. Study is published by Novikoff (1967) and Clermont et al. (1981) the CMPase being a hydrolase which participates to a major part in the sequestration process and vesicular packaging from the GERL system. The enzyme is carried on towards the cell surface bound to the membrane of transport vesicles. Our observations suggest a possible incorporation of glycoconjugates in the plasmalemm by involvement of CMPase. In addition, the enzyme takes part in the endocytotic reuptake of glycoconjugates having lost their complete function with recycling and rebuilding in the GERL and Golgi apparatus. By using antigen provoked mononuclear and neutrophilic leucocytes the membrane bound response of CMPase is seen to be very distinct. The same is true for enterocytes exposed for a short-time ischemia. A strictly localized appearance of the CMPase in close vicinity to the couplings of short-time ischaemic muscle fibres in apparently of relevancy fr restructuring and availability of membrane bound glycoconjugates. This suggest a direct influence on the mechanism of excitation-contraction couplings of skeletal muscle fibres.