Enzymes Involved in the Reversible Phosphorylation in Microvessels of the Brain

The Blood-Brain Barrier (BBB) of vertebrates is located in the microvessels of the brain. The endothelial cells coating these capillaries are sealed together by tight junctions to restrict any uncontrolled diffusion of water soluble substances across the BBB. The transport of polar substances including nutrients and waste products into and out of the brain is mediated by specific transport mechanisms. Brain capillaries have been shown to be very active in the reversible protein phosphorylation which led to the hypothesis of a rapid control of brain microvessel functions by protein kinases and phosphatases (Pardridge et al., 1985). There are hints that all groups of second messenger dependent protein kinases are present in the endothelial cells of these vessels (Olah et al., 1988).