ABSTRACT
Although it has been known at least from the beginning of this century that enzymes are present in human milk, and that more than 20 different enzyme activities have now been demonstrated in milk 1–4 (Table 1), no extensive study of the full spectrum of enzymes in milk has yet been made. Hence, the number of enzymes in milk is probably underestimated. With a few exceptions, our knowledge is based on a single or a few reports on each enzyme, often merely demonstrating the presence of the respective enzyme activity in a limited number of milk samples. However, recent studies, e.g., of the lipases in human milk (see Chapter 16) have shown that enzymes secreted in milk may function in the recipient infant. In this chapter we have tried to summarize some of the current knowledge on enzymes in human milk, excluding the lipases. In doing so we have preferred to emphasize some general aspects rather than to discuss each enzyme presently known to be a component of milk. Enzymes Demonstrated to be Present in Human Milk<xref ref-type="fn" rid="fntab6_1_1"> <sup>a</sup> </xref> https://www.niso.org/standards/z39-96/ns/oasis-exchange/table">
Enzyme
E.C.#
MW
N-Acetyl-β-hexosaminidase
3.2.1.4
141,000
Acid phosphatase
3.1.3.16
85,000
Adenosine triphosphate
3.6.1.3
620,000
Alanine aminotransferase
2.6.1.2
115,000
Aldolase
4.1.2.13
120,000
Alkaline phosphatase
3.1.3.1
86,000
α-Amylase
3.2.1.1
96,000
β-Amylase
3.2.1.2
202,000
Aspartate aminotransferase
2.6.1.1
78,600
Catalase
1.11.1.6
232,000
Cholinesterase
3.1.1.8
315,000
Elastase, anionic
3.4.21.11
25,900
Glucose phosphate isomerase
5.3.1.9
145,000
β-Glucuronidase
3.2.1.31
280,000
γ-Glutamyl transpeptidase
2.3.2.2
3,000,000
Glutathione peroxidase
1.11.1.9
95,000
Inorganic pyrophosphate
3.6.1.1
71,000
Lactate dehydrogenase
1.1.1.27
140,000
Lactose synthase
2.4.1.22
60,000
Lipase, bile-salt stimulated
3.1.1.3
107,000
Lipoprotein lipase
3.1.1.3
42,000
Lysozyme
3.2.1.17
15,000
Malate dehydrogenase
1.1.1.37
54,000
Myeloperoxidase/lactoperoxidase
1.11.1.7
93,000
Plasmin
3.4.21.7
75,000
Ribonuclease
4.7.7.16
13,800
Sulfhydryl oxidase
85,000
Superoxide dismutase
1.15.1.1
32,000
Trypsin, anionic
3.4.21.4
24,000
Xanthine oxidase
1.2.3.2
181,000
Compiled from References 1 to 6.
