Cleaves the beta-1,4-linkages between beta-D-galactose and alpha-L-3,6-anhydro-galactose residues in agarose. Cleaves agarose in a random manner with retention of the anomeric-bond configuration, producing beta-anomers that give rise progressively to alpha-anomers when mutarotation takes place. Hydrolysis of (1->4)-beta-D-galactosidic linkages in agarose, giving the tetramer as the predominant product. kcat is 150 sec(-1). Monomer. When cells are grown with the low sulfated agar. Proteolytically cleaved into mature beta-agarase A catalytic chain (AgaAc). Belongs to the glycosyl hydrolase 16 family.