Heme synthesis in Crithidia deanei: influence of the endosymbiote.

The activity of the following enzymes involved in the biosynthesis of porphyrins was determined in endosymbiote-free and endosymbiote-containing Crithidia deanei grown in a chemically defined medium: succinyl Coenzyme A synthetase (Suc.CoA-S), 5-aminolevulinate synthetase (ALA-S), 4,5-dioxovaleric acid transaminase (DOVA-T), 5-aminolevulinate dehydratase (ALA-D), porphobilinogenase (PBGase), deaminase and heme synthetase (Heme-S). The amount of 5-aminolevulinic acid (ALA) and porphobilinogen, porphyrins and heme was also determined. ALA and PBG were detected in C. deanei. The levels of free porphyrins was low. Heme concentration was nil. The activity of ALA-D, deaminase and PBGase was not detected in C. deanei. The activity of Suc.CoA-S and ALA-S were twice higher in symbiote-containing than in aposymbiotic C. deanei. Aposymbiotic cells had a higher activity of DOVA-T than symbiote-containing cells. The level of Heme-S, measured using protoporphyrin as substrate, was twice as high in symbiote-containing than in symbiote-free cells.

2. ALA and PBG were detected in C. drunei. The levels of free porphyrins was low. Heme concentration was nil.
3. The activity of ALA-D, deaminase and PBGase was not detected in C. deanei.
4. The activity of Suc.CoA-S and ALA-S were twice higher in symbiote-containing than in aposymbiotic C. deanri. Aposymbiotic cells had a higher activity of DOVA-T than symbiote-containing cells.
5. The level of Heme-S. measured using protoporphyrin as substrate, was twice as high in symbiotecontaining than in symbiote-free cells. -

INTRODUCTION
Crithidia deanei, a flagellated trypanosomatid protozoan, isolated from the hemipteran Zelus leucogramus and harboring endosymbiote (Mundim er al., 1974) was made aposymbiotic with high doses of chloramphenicol (Mundim and Roitman, 1977). A chemically defined medium supports growth of both normal and aposymbiotic strains (Roitman et ul., 1972). Such intracellular symbiotes are integrated into the physiology of the host cell (McGhee and Cosgrove, 1980). It was shown that the presence of the endosymbiote influenced significantly the composition of carbohydrates exposed on the cell membrane and slightly the surface anionic groups of C. deanei (?da et al., 1984).
Nutritional studies carried out in flagellate trypanosomatids have clearly demonstrated that heme compounds, including hemin, hematin or hemoglobin, are essential growth factors (Lwoff, 1951). Possibly such nutritional requirements are associated with their inability for heme biosynthesis (Roitman et al., 1972;Chang and Sassa, 1975 such as Blastocrithidia culicis, Crithidia oncopelti and C. deanei-bearing symbiote do not require heme substances for growth (Mundim and Roitman, 1977;Chang and Sassa, 1975). Presumably the bacterial symbiotes supply the host trypanosomatids with heme biosynthetic capability (Chang and Sassa, 1975). However, how the presence of symbiote may regulate the enzyme activities in the flagellate heme biosynthetic pathway is not completely understood. Taking into account the currently accepted porphyrin pathway (Fig. I), we have investigated several enzymic activities in the heme biosynthetic chain in symbiote-bearing and symbiote-free strains of C. deunei. The results obtained in C. deanei suggest that the presence of the endosymbiote increases the activity of some enzymes and early porphyrin precursors of the heme biosynthetic pathway.

Symbiote-bearing
Crithidiu deunei (ATCC 30255) was maintained by weekly transfers in a chemically defined medium (Roitman PI al., 1972). without hemin. distributed in 5-ml volumes in screw-capped tubes. The aposymbiotic strain required nicotinamide (3 mg%) and hemin (I pg%) which was added to the same defined medium.
For the experiments, cells were grown in 3 I. flasks containing 1.5 1. of the defined medium referred to above. The medium was autoclaved at 120 C for 20 min. The inoculum consisted of 30 ml of 48-hr culture; about 6 x IO' cells were inoculated per flask. After 48 hr of incubation the cells were collected by centrifugation (2OOOg for IOmin) at 4 C and were washed 2 times in cold 25 mM Tris+HCl buffer. 250 mM sucrose, 5 mM KCI, pH 7.0; glass powder (5 g/g cells, wet weight) was added to the washed pellet, and the mixture was ground in a mortar for Smin at 4 C. This procedure resulted in a complete breakage of the cells, as  A calibration curve was obtamed following the method described by Porra and Jones (1963). Hemin was measured by the same procedure in the 580 g supernatant of C clcrrrrc,l. . Samples were incubated anacrobically with gentle agitation at 37 C in the presence of light (2500 lx). The reaction was stopped by addition of I ml of 10% TCA. ALA synthesized was assayed in the supernatant according to Mauzerall and Granick (1956) and the remaining DOVA following the method of Milligan and Baldwin (1967).
. ~-Ami,lok~,l,u/inu~~, &h,vc/rtr/~~w~ (ALA -D ). This was ahsayed in the supernatant in 0.05 M. Tris HCI buffer (pH 7.4) following: (a) the procedure described by Tigier PI ul. (1970): (b) ALA-D activity was also measured using the same incubation mixture as in (a)  of FeSO, from the side arm of the tube and further incubated for I hr with constan shaking. The final volume was 4.2 ml. The reaction was stopped by opemng the tube and adding I .O ml of pyridine. then 0.5 ml of I N NaOH and I .O ml of iodoacetamide.
The rcsultmg mixture was equally divided between two cuvcttes: 2 mg of solid Na&O, was added to one cuvette and 0.05 ml of 3 mM K, Fe(CN), to the other. Heme formed was calculated using the equation of Porra and Jones (1963) One unit of enzyme activity was dclincd as the amount of enzyme which catalyzes the formation of I nmol of product and or the consumption

RESULTS
As shown in Fig. 2 ALA and PBG were detected in both symbiote-containing and symbiote-free C. deanei. However, these porphyrin precursors were increased in symbiote-containing flagellates. The levels of free porphyrins was very low. Heme concentration was nil. The activities of Suc.CoA-S, ALA-S, DOVA, ALA-D, PBGase, deaminase and Heme-S activities are shown in Fig. 3. The SucCoA-S activity was more than twice higher in the symbiote-containing than in the symbiote-free flagellates. Similar results were observed with the ALA-S activity. The level of ALA-D was very low: this enzyme activity was not markedly altered even in the presence of Zn2+ ions, Also, in both strains of C. deanei the PBGase activity was negligible whereas some functionality was detected in the symbiote-free strain, when evaluated by the PBG consumed.
A similar pattern was observed with deaminase activity, but the enzyme functionality, measured as PBG consumed, was increased in the symbiote-containing C. deanei as compared with symbiote-free cells. Heme-S was active in C. deanei cells as evaluated by meso and protoheme formed. However, in the later case the enzyme activity was markedly increased in the symbiote-bearing flagellates. When the enzyme activity was measured as deuteroheme formed a certain Heme-S functionality was detected only in the symbiote-free cells.
In the present work WC demonstrate that the bacterial symbiotes increase the activity of several enzymes associated with the heme biosynthetic pathway of C. &unei. Extracts of both symbiote-free and symbiotecontaining C. deanei showed the presence of ALA and PBG. However, in symbiote-bearing flagellates the concentration of ALA and PBG was markedly increased. Since both porphyrin precursors are not components of culture medium they were synthesized by the cells. Previous nutritional studies revealed that Leishmuniu turentolae (Gaugham and Krassncr, 1971), B. culicis and C. oncolpelti (Chang and Sassa, 1975) are unable to utilize ALA and PBG. In addition it was demonstrated that at least radioactive ALA enter readily into hemoflagellates (Gaugham and Krassner, 1971). These nutritional studies. the low amount of porphyrins and nil heme concentrations observed in the present work and previously in T. cm5 (Salzman et al.. 1982) and the results reported in both symbiote-containing and symbiotefree trypanosomatids (Chang and Sassa. 1975) suggest that hemoflagellates may be in general incapable of adequate tetrapyrrole pathway biosynthesis. It is well established that succinyl CoA participates in the committed step of porphyrin biosynthesis in animals and bacteria: its condensation with giycine produces aminolevulinic acid (ALA). Therefore Suc.CoA-S can be involved in the tetrapyrrolc pathway (Batlle clt al.. 1975. The Suc.CoA-S activity was significantly higher in the symbiotc-containing C. dearzri as compared with symbiote-free flagellates. A similar finding has been rcportcd carlicr with B. culi(,i.s and C. oncqx~lfi: the rate of incorporation of carbon from glycinc was greater for symbiotecontaining trypanosomatids than for those without symbiotcs (Chang and Sassa, 1975).
Two routes for ALA formation have been proved to exist together in the same cell: the direct synthesis Both ALA pathways were looked for. L-Alanine-4,5-dioxovalcric acid transaminase (DOVA-T) utilizes L-alaninc as the amino donor and 4.5-dioxovaleric acid as the amino acceptor (Varticovski c/ (11.. 1980). The reaction products are ALA and pyruvatc.
The study of DOVA-T has revealed that the activity of this enzyme is nearly six times higher in the symbiotc-free C. tkmci cells. when the activity was cxpresscd as a function of ALA formed. In contrast, the DOVA-T activity was highest in C. deunei when evaluated by the amount of DOVA consumed.
However, it is known that DOVA might be metabolized via other routes and in this case only the amount converted to ALA could be relevant. ALA-S. which catalyzes the condensation of Suc.CoA with glycine with the production of ALA, the first product of the biosynthetic chain of heme. was significantly higher in the symbiote-containing strain than in the symbiote-free cells. Therefore, we concluded that in c'. tkunpi harboring cndosymbiote ALA is synthesized via ALA-S. while in the symbiote-free cells its synthesis occurs via DOVA-T. thus once indicating the contribution of the bacterial symbiote for the heme biosynthetic pathway. ALA-S was equally active in strains of Euglenu grucilis (Beale et rd., 198 I) and in T. cruzi (Salzman et (I/., 1982). 5-Aminolevulinic acid dehydratase (ALA-D) catalyzes the condensation of 5-aminolevulinic acid into porphobilinogen (PBG). As previously observed in T. cruzi (Salzman et al.. 1982). it was also difficult to detect ALA-D activity in C. deunei extracts in either the symbiote-containing or symbiote-free cells under the optimal conditions: its level was almost negligible. The enzyme was also measured by supplementing the incubation mixture with a known activator such as Zn'+ ions (Brocklehurst et ul., 1980). Nevertheless the enzyme activity did not increase markedly in any of the extracts under study.
The PBGase and deaminase activities could not be detected either in the symbiote-bearing or the symbiote-free C. deunei. However the specific activity of uroporphyrinogen I synthetase (deaminase) was increased in symbiotei-ontaining flagellates (Chang and Sassa, 1975). Such different results may be attributed to the use of different trypanosomatids.
In T. cruzi PBGase and dcaminase activities were also absent or inactive (Salzman PI ill.. 1982).
Heme-synthetase (Heme-S) catalyzes the addition of iron to different porphyrins. and particularly to protoporphyrin, in the formation of heme. This enzyme has a specific requirement for Fe" but not for the porphyrin substrate: either meso or dcuteroporphyrins may function as substrates but, in the cell, only protoporphyrin would be available. In our experiments the activity was always measured by using proto, mcso and deuteroporphyrin as substrate. There could not be detected an actual ditrerencc in the Heme-S activity of both strains of C. dcwmei when mesoporphyrin was the substrate. When the activity was expressed as the amount of dcuterohemc formed only the symbiote-free strain showed a certain functionality.
However, the level of Heme-S activity. measured with protoporphyrin as substrate. was significantly higher in the symbiote-containing cells suggesting that the bacterial symbiotes endow the host flagellates with an adequate heme biosynthetic capability.
It is interesting that in C. rkunri the activity of the enzymes usually confined to the cytosol of most cells including ALA-D, PBGase and deaminase is low, while that of the particulate enzymes such as Suc.CoA, ALA-S, DOVA-T and heme synthetase is readily detectable.
A comparable finding was previously noted in T. cruzi (Salzman et al., 1982). These results would suggest that Trypanosomatidae have lost part of their heme biosynthetic ability. In conclusion, the fact that C. deunei harboring endosymbiote does not require hemin in its culture medium, suggest that the presence of the bacterial endosymbiote increases a certain limited heme biosynthetic capacity in the flagellates supplying them with certain enzymes and early porphyrin precursors of this pathway. Also, the present work confirms, as suggested earlier (Esteves ef al., 1982), that C. denner is an excellent experimental model for study of the symbiote-host interactions.