The word cleave is defined as to split or sever. The word after in the sentence BrAAP activity which cleaves after branched-chain amino acids means that splitting occurs following the branched-chain amino acids meet with bacteria.

The branched amino acids is used by the organism in protein where the polypeptide chain should be branched, other than that i think they're more or less just involved in transamination reaction and aminoacid-biosynthesis

It's not what "is" but what are ibcaa's

And it's "Instantized Branched Chain Amino Acids"

Roya Riazi has written:

'Branched chain amino acid metabolism'

The 3 basicshapes of carbon molecules are ring, branched, and straight chain.