W.C.M.C. Kokke

Bio: W.C.M.C. Kokke is an academic researcher from Stanford University. The author has contributed to research in topics: Sterol & Zooxanthellae. The author has an hindex of 19, co-authored 24 publications receiving 874 citations. Previous affiliations of W.C.M.C. Kokke include Scripps Institution of Oceanography.

Recent progress in the marine sterol field

Abstract: This paper covers recent work much of it from the authors' laboratory dealing with novel 3-hydroxy marine sterols possessing unusual side chains, which have hitherto not been encountered in terrestrial sources. Aside from a description of the proof of structure and stereochemistry of these sterols, attention is also drawn to plausible models of biosynthesis and to the possible biological role in membrane function.

Sterol patterns of cultured zooxanthellae isolated from marine invertebrates: Synthesis of gorgosterol and 23-desmethylgorgosterol by aposymbiotic algae

Abstract: Quantitative sterol compositions of cultured zooxanthellae isolated from various Pacific and Atlantic invertebrate hosts: Zoanthus sociatus (a zoanthid), Oculina diffusa (a scleractian coral), Tridacna gigas (a giant clam), Melibe pilosa (a nudibranch), and Aiptasia pulchella (a sea anemone) are reported. The results clearly demonstrate large differences in sterol patterns of zooxanthellae and that there is no obvious relationship between the taxonomic affiliation of the host and the sterol pattern of its isolated symbiont. The sterols of the zooxanthellae of O. diffusa (Cnidaria) and T. gigas (Mollusca) are qualitatively equivalent. Based on the structures of the two major free sterols synthesized by each alga, the zooxanthellae from different hosts were separated into three distinct groups. It was also found that an aposymbiotic alga can synthesize the unique marine sterols gorgosterol and 23-desmethylgorgosterol. Most of the sterols were identified by using mass spectroscopy and 360-MHz proton magnetic resonance. Spectroscopic data are reported for four novel sterols—(23,24R)-dimethyl-5α-cholest-(22E)-en-3β-o l, 23-methyl-5α-cholest-22E-en-3β-ol, cholesta-5,14-dien-3β-ol, and 4α-methyl-5α-cholesta-8(14)-24-dien-3β-ol.

Relationship Between Petroleum Composition and Depositional Environment of Petroleum Source Rocks

Abstract: Crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters, as demonstrated with a sample suite of nearly 40 oils. A novel parameter based on the presence of C30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine-derived organic matter. A second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin. Sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions. Concentrations of high molecular-weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes. Certain algal-derived nonmarine oils may show little high molecular-weight paraffin response. Oils from carbonate sources (with a few exceptions) can be distinguished by having low pristane-phytane ratios, low carbon preference indexes, and high sulfur contents. Gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis.