Synthesis of phenylalanine and production of other related compounds from phenylpyruvic acid and phenylacetic acid by ruminal bacteria, protozoa, and their mixture in vitro.

Abstract

Phenylalanine (Phe) synthesis and the production of other related compounds by mixed ruminal bacteria (B), protozoa (P), and a combination of the two mixture (BP) in an in vitro system were quantitatively investigated using phenylpyruvic acid (PPY) and phenylacetic acid (PAA) as substrates. Rumen microorganisms were collected from fistulated goats fed lucerne cubes (Medicago sativa) and a concentrated mixture twice a day. Microbial suspensions were anaerobically incubated at 39°C for 12 h. Phe and some other related compounds in both supernatants and microbial hydrolysates of the incubations were analysed by HPLC. A large quantity of Phe was produced from both PPY and PAA not only in B but also in P. In B suspensions, free Phe also accumulated in the medium only when PPY was used as a substrate. The ability of B to synthesize Phe from both PPY and PAA (expressed as unit 'per microbial nitrogen') was 5.1 and 24.8% higher than P, respectively. Phe production from PPY in B and P was 43.5 and 55.2% higher than that from PAA. Large amounts of PAA (17-27%) were produced from PPY in all microbial suspension and production amounts were similar in B and P. Small amounts of benzoic acid (BZA) were produced from PPY and PAA in B, P, and BP, and higher BZA production was observed in P as compared to B. Phenylpropionic acid (PPR) was produced in B from both PPY and PAA, but not in P or BP. A trace amount of phenyllactic acid (PLA) was detected only from PPY in B. Higher concentrations of an unknown compound from PPY and PAA were found to be accumulated in the body protein of B and also in the medium of P, and production of the compound from both PPY and PAA was also higher in B than P.Key Words benzoic acid; phenylacetic acid; phenylalanine synthesis; onic acid; phenylpyruvic acid; rumen bacteria; rumen protozoa phenyllactic acid; phenylpropiIn phenylalanine (Phe) anabolism by rumen bacteria, phenylacetic acid (PAA) has been observed to be reductively carboxylated to form phenylpyruvic acid (PPY) and then transaminated to form Phe (Allison, 1965;Allison et al., 1984;Kristensen, 1974). Bacteria identical with the ruminal organisms that use PAA in Phe biosynthesis (Allison, 1966;Allison and Robinson, 1967a;Allison et al., 1984;Gehring and Daniel, 1971) have been found in other anaerobic environments (E3rown and Moore, 1960). A similar metabolic mechanism by the rumen bacteria for other aromatic amino acids like tryptophan (Allison and Robinson,

Tryptophan biosynthesis and production of other related compounds from indolepyruvic acid by mixed ruminal bacteria, protozoa, and their mixture in vitro.

“…In the B suspension, large amounts of Trp were produced from IPA in the supernatants after 6-and 12-h incubations (Table 1). A small portion of Trp produced from IPA was incorporated into bacterial protein in 6-and 12-h incubations (Table 1), different from the results concerning Trp production from IND and serine (N. Mohammed et al, 1999) and Phe production from phenylpyruvate (PPY) and PAA reported by Amin and Onodera (1997). In total, 23.3 and 33.4% of IPA were converted to Trp after 6-and 12-h incubations, respectively.…”

“…The continuous engulfment of bacteria by protozoa can lower the number of bacteria and decrease the total bacterial activity to synthesize Trp from IPA. In this connection, Amin and Onodera (1997) also reported the same effect during the production of Phe from PPY and PAA by B, P, and BP suspensions.…”

Effects of salinomycin and vitamin B6 on in vitro metabolism of phenylalanine and its related compounds by ruminal bacteria, protozoa and their mixture.

“…The large amounts of PAA produced from PPY and the production of PAA in the B, P and BP suspensions with and without SL and B 6 are shown in Table 1. PAA production from PPY was almost similar to a result reported previously (Amin and Onodera, 1997b).…”

“…PAA was converted mainly to Phe, and the production of Phe in B, P and BP suspensions with and without SL and B 6 is shown in Table 2. The production of Phe from PAA was almost similar to results reported previously (Amin and Onodera, 1997b). In B suspensions without additives, 174 and 240 µmol/g MN (168 and 231 µM) of PAA were converted to Phe, while the production of Phe with SL tended to be inhibited, though not significantly, by 12.1 and 3.8% during the 6 and 12 h incubation periods.…”

“…PPY was converted mainly to Phe and the production of it in B, P and BP suspensions with and without SL and B 6 is shown in Table 1. The production of Phe from PPY was almost similar to the results reported previously (Amin and Onodera, 1997b). In the case of PPY metabolism, only the values during the 6 h incubation period have been taken into consideration for discussion, because PPY was completely utilized by all the microbial suspensions during the 12 h incubation period.…”