Ochromonas malhamensis

Fig. 1. Typical growth curve in thiamine assay with Ochromonas malhamensis [Baker et al. (B15)].

Knowledge of the coenzyme forms of vitamin Bi2 has increased steadily. The first coenzyme of Bi2 isolated from bacteria had similarities to pseudovitamin Bi2 it contained adenylic acid instead of 5,6-dimethyl-benzimidazole, but differed in lacking cyanide and having an extra molecule of adenine which was assumed to be bound to the cobalt atom by the coordination site, often occupied by cyanide (B24). This coenzyme, adenylcobamide, was completely inactive for Ochromonas malhamensis, but active for Escherichia coli 113-3. 

Ochromonas malhamensis responds to vitamin Bi2, but not to pseudovitamin Bi2 E. coli responds to both forms. Later other coenzymes were isolated (B25). One contained benzimidazole (BC), the other... 

F2. Ford, J. E., Microbiological assay of vitamin B12. The specificity of the requirement of Ochromonas malhamensis for cyanocobalamin. Brit. J. Nutrition 7, 299-306 (1953). 

Kl. Kamikubo, J., and Oguni, Y., Microbiological determination of vitamin B12 with Ochromonas malhamensis. J. Vitaminol. 5, 51-60 (1959). 

Squalene 2,3-epoxide (2) was converted into cycloartenol (3) in 22% yield by a microsomal fraction from Ochromonas malhamensis (an alga). Retention of configuration at C-19 (the cyclopropyl carbon) is observed. 

The possibility exists that the C-20 carbonium ion formed initially could be neutralized not as just indicated but by water at an anionic enzyme center to yield a protosterol (3-A) which could then reorient on the enzyme and lose water to yield cycloartenol (2-A) indeed, (3-A) is effectively incorporated into poriferasterol (4-B) by Ochromonas malhamensis (Palmer ef al., 1978). 

Lactobacillus leichmannii, E. coli, Ochromonas malhamensis, and Euglena gracilis. 

As with euglenoids, the Bis requirement is probably phyletic. Although the strains tested are an infinitesimal sampling of the total number of species, the tests have included members of several of the diverse groups within the chrysomonads. These studies have not yet gone beyond demonstration of the need for cyanocobalamin. Poteriochromonas stipitata resembled Ochromonas malhamensis in not responding to Bis-like compounds active for E. coli and Lactobacillus leichmannii (Barber et al., 1953). 

This compound is probably unique among the naturally occurring vitamin Bu-like compounds so far known in that it is active against pernicious anemia and for the chick (Bernhauer, 1955) and the flagellate Ochromonas malhamensis (Table II) (a microorganism which, as mentioned earlier, displays a specificity for vitamin Bw similar to that of birds and mammals (Ford, 1953)) as well as for E. coli and L. leichmannii. The chromatographic and ionophoretic properties illustrated in Fig. 1, with the other physical properties given by Friedrich and Bernhauer (1953), clearly differentiate Factor III from the cobalamins and from the other vitamin Bir-like factors. Its chemical relationship to these other compounds has not yet been established. 

Despite its biological importance, the mechanism of transport of the thioether in the cell has been investigated only in fe ar instances. A saturable transport system has been described in the protozoan Ochromonas malhamensis the apparent K value calculated for MTA is 0.30 mM, significantly lower than the K of Ado-Met and methionine,thus indicating a specificity of the system towards MTA. 

The labeled oxidosqualene (XXIII) was incorporated very well by a microsomal fraction from the chosen organism Ochromonas malhamensis to give in good yield a labeled cycloartenol (XXIV). 

Many studies have been conduded on the biosynthesis of sterols in Ochromonas malhamensis and Sarcinochrysis sp., which it is not possible to cover within the framework of this introduction (Smith, Goad, and Goodwin, 1972 Tsai, Adler, and Patterson, 1975 Knapp et cd., 1977 Nicotra et al, 1980, 1984, 1985). The order Ochromonales is charaderized by the major presence of 24-ethyl-cholesta-... 

Knapp, F.F., Creig, J.B., Goad, L.J., and Goodwin, T.W. (1977) The conversion of 24-ethylidene-sterols into poriferasterol by Ochromonas malhamensis. Phytodiemistry, 16,1683-1688. 

Nicotra, F., Ronchetti, F., Russo, G., Toma, L., Gariboldi, P., and Ranzi, B.M. (1984) Stereochemistry of hydride migration from C-24 to C-25 in the biosyntiiesis of poriferasterol in Ochromonas malhamensis. J. Chem. Soc. Chem. Common., 383-384. 

Tsai, L.B., Adlec J.H., and Patterson, G.W. (1975) Metabolism of 24-dihydrolanosterol in Ochromonas malhamensis and Chlordla elUpsoides. Phytodiemistry, 14,2599—2600. 

---