Pravastatin is a tissue-selective inhibitor of HMG-CoA reductase, a key enzyme in cholesterol biosynthesis. This compound was obtained by the microbial hydroxylation of mevastatin(ML-236B). Pravastatin was primarily discovered in the urine of dog as a minor active metabolite of mevastatin. Various fungi were tested for their transformation capability to find some Zygomycetes Mucor hiemalis converted mevastatin mainly to pravastatin. These fungi, however, were found to not tolerate increase in the amount of mevastatin added to the culture broth. Amycolata autotrophica of actinomycetes, the isolates from the soil sample collected in Australia, were found to have strong transformation activity with by-product in spite of its tolerance to the substrate. After further energetic screening for fresh isolates of actinomycetes, Streptomyces carbophilus was discovered as a potent converter with a limited amount of by-product. S. carbophilus was also tolerable to a higher amount of mevastatin in the culture broth. In this way, Streptomyces carbophilus having capability of industrial- scale production of pravastatin were isolated from soil sample collected in Australia. The hydroxylation of mevastatin to pravastatin in Streptomyces carbophilus was catalyzed by a cytochrome P-450sca monooxygenase system. The P-450sca system had turned out to exist in the soluble fraction and to be composed of only two components, P-450sca and flavoprotein. Therefore, a novel character of P-450sca system in prokaryote was suggested.
Isolation of actinomycetes is an indispensable step in the screening programs of industrially useful strains as well as in the ecological study of microorganisms. During the past 10 years, the author and his co-workers have studied the selective isolation methods of soil actinomycetes. A new medium and a variety of new methods were developed for the preferential isolation of the general and particular genera of actinomycetes. In addition, some ecological factors related to the distribution of these organisms in soils were clarified.
Dr. Shinobu was awarded for his distinguished contributions by the Society for Actinomycetes, Japan. This paper outlines the personal history and actinomycete researches of Dr. Shinobu, consisting of 1) personal history, 2) starting point of studying actinomycetes, 3) studies on establishment of criteria for the identification of actinomycetes species, 4) summary of the studies on actinomycetes.