Table 1. Overview of Lysosomal Enzymes with pH Optima at Approximately pH 4.0–4.8 and Other Components as Recorded by Tappel, Adapted from ref (30).

enzyme family	enzyme	substrate specificity	pH optima	experimental substrate/enzymic source	major natural substrates
nucleases	acid deoxyribonuclease	phosphodiester linkages of DNA	4.5	DNA/spleen	DNA
phosphatases	acid pyrophosphatase	flavin adenine dinucleotide, ATP	4.0	ATP and flavin adenine dinucleotide/liver lysosomes	flavin adenine dinucleotide and ATP
enzymes hydrolyzing the carbohydrate chains of glycoproteins and glycolipids	β-N-acetyl hexosaminidase	β-N-acetyl glucosaminides	4.0–4.6	nitrophenyl-β-N-acetyl glucosaminide/liver lysosomes	β-N-acetyl hexosaminides in glycoproteins and glycolipids
		β-N-acetyl galactosaminides
	α-N-acetyl hexosaminidase	α-N-acetyl glucosaminides	4.5	nitrophenyl-α-N-acetyl glucosaminide/testis	heparan sulfate
		α-N-acetyl galactosaminides
	α-mannosidase	α-mannosides and related glycosides	4.6–5.0	not recorded	α-mannosides in glycoproteins
	sialidase	sialic acid derivatives	4.0–4.4	sialyllactose and glycoprotein/liver and kidney lysosomes	glycoproteins and glycolipids
	O-seryl-N-acetyl-galactosaminide glycosidase	seryl acetyl galactosaminide	4.4	submaxillary gland glycoprotein/kidney and liver lysosomes	seryl acetyl galactosaminide in glycoproteins
enzymes degrading glycosaminoglycans	β-glucuronidase	all aliphatic and aromatic β-d-glucosiduronic acids	4.5–5.2	phenolphthalein β-glucuronide/liver lysosomes	polysaccharides, mucopolysaccharides, and steroid glucuronides
	arylsulfatase A	nonspecific, aryl sulfates	4.9	nitrocatechol sulfate/liver	aryl and cerebroside sulfates, chondroitin 4-sulfate
enzymes degrading lipids	triglyceride lipase	triglycerides	4.2	glycerol tridecanoate/liver and kidney lysosomes	triglycerides
	phospholipase	phospholipids	4.5	lecithin, lysolecithin, and phosphatidyl ethanolamine/liver lysosomes	lecithin, lysolecithin, and phosphatidyl ethanolamine
	esterase	fatty acid esters	3.6–4.0	fatty acid esters of p-nitrophenol/liver and kidney lysosomes	fatty acid esters