Movement of the ligand/receptor complex in rhodopsin (Rh) has been traced. Bleaching of diazoketo rhodopsin (DK-Rh) containing 11- cis -3-diazo-4-oxo-retinal yields batho-, lumi-, meta-I-, and meta-II-Rh intermediates corresponding to those of native Rh but at lower temperatures. Photoaffinity labeling of DK-Rh and these bleaching intermediates shows that the ionone ring cross-links to tryptophan-265 on helix F in DK-Rh and batho-Rh, and to alanine-169 on helix D in lumi-, meta-I-, and meta-II-Rh intermediates. It is likely that these movements involving a flip-over of the chromophoric ring trigger changes in cytoplasmic membrane loops resulting in heterotrimeric guanine nucleotide–binding protein (G protein) activation.

One of the most interesting groups of substances of marine origin, from structural and pharmacological points of view are polyether toxins, which generally pre-sent a great diversity in size and potent biological activities. The subject of this review is limited to okadaic acid (OA). It was the first example of a group of polyether toxins produced by marine microalgae, which is responsible for the natural phenomena known as Diarrhetic Shellfish Poisoning, DSP red tides. These toxins are accumulated in the digestive glands of the shellfish with a disastrous effect upon the shellfish industry in many parts of the world. Thus, it has been demonstrated that OA is a highly selective inhibitor of protein phosphatases type 1 (PP1) and 2A (PP2A), subsequently that it causes dramatic increases in phosphorylation of numerous proteins as well as being a potent tumour promoter. For that reason, OA is an extremely useful tool for studying the cellular processes that are regulated by reversible phosphorylation of proteins as signal transduction, cell division and memory.

The study of marine natural products for their bioactive potential has gained strength in recent years. Oceans harbor a vast variety of organisms that offer a biological and chemical diversity with metabolic abilities unrivalled in terrestrial systems, which makes them an attractive target for bioprospecting as an almost untapped resource of biotechnological applications. Among them, there is no doubt that microalgae could become genuine “cell factories” for the biological synthesis of bioactive substances. Thus, in the course of inter-laboratory collaboration sponsored by the European Union (7th FP) into the MAREX Project focused on the discovery of novel bioactive compounds of marine origin for the European industry, a bioprospecting study on 33 microalgae strains was carried out. The strains were cultured at laboratory scale. Two extracts were prepared for each one (biomass and cell free culture medium) and, thus, screened to provide information on the antimicrobial, the anti-proliferative, and the apoptotic potential of the studied extracts. The outcome of this study provides additional scientific data for the selection of Alexandrium tamarensis WE, Gambierdiscus australes, Prorocentrum arenarium, Prorocentrum hoffmannianum, and Prorocentrum reticulatum (Pr-3) for further investigation and offers support for the continued research of new potential drugs for human therapeutics from cultured microalgae.