Type III Pyridoxal 5-phosphate (PLP)-Dependent Enzyme Alanine Racemase-like 1. This subfamily is composed of uncharacterized bacterial proteins with similarity to bacterial alanine racemases (AR), which are fold type III PLP-dependent enzymes containing an N-terminal PLP-binding TIM-barrel domain and a C-terminal beta-sandwich domain. AR exists as homodimers with active sites that lie at the interface between the TIM barrel domain of one subunit and the beta-sandwich domain of the other subunit. It catalyzes the interconversion between L- and D-alanine, which is an essential component of the peptidoglycan layer of bacterial cell walls. Members of this subfamily may act as PLP-dependent enzymes.

Exostosin family. The EXT family is a family of tumour suppressor genes. Mutations of EXT1 on 8q24.1, EXT2 on 11p11-13, and EXT3 on 19p have been associated with the autosomal dominant disorder known as hereditary multiple exostoses (HME). This is the most common known skeletal dysplasia. The chromosomal locations of other EXT genes suggest association with other forms of neoplasia. EXT1 and EXT2 have both been shown to encode a heparan sulphate polymerase with both D-glucuronyl (GlcA) and N-acetyl-D-glucosaminoglycan (GlcNAC) transferase activities. The nature of the defect in heparan sulphate biosynthesis in HME is unclear.