Studies on lactoferrin, a metal binding protein in human milk : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University

a copy to be downloaded by an individual for the purpose of research and

private study only. The thesis may not be reproduced elsewhere without

the permission of the Author.

STUDIES ON LACTOFERRIN,

A METAL BINDING PROTEIN IN HUMAN MILK

A T h e s i s p r e s e n t e d i n par t i al ful film e n t o f t h e requi reme n t s f o r t h e degree o f

Doc t o r o f Philo s o phy in Chemis t ry a t Mas s ey U n i ve rsi ty

Je ffrey Erne s t Pl o�m an 1 979

"It s a bit late in t he day to introduce the idea now , but almost any mammal's milk would be easi er to modi fy than co w's milk . Pig's milk i s ac tually nearest t o hum an milk.

Camel milk and mare's milk have a bet ter balance for humans . S heep's milk is OK and so is goat's . Reindeer milk would be a bit fat , dog1s milk a bit thin. Now, o t ter's milk could be just righ t . Perhaps we shoul d look into i t ."

M. Bateman ("Sunday Times" - London , 1 6 March 1 9 75)

( i i i )

ABSTRACT

Lactof errin ( L f) , iso l ated from human co lostrum , has b e en compl exed with a vari e ty o f transi t ion me tal i o ns . I n addi tion t o binding two iron ( III) o r c o pper ( I I) i ons i t strongly and s peci fically binds t wo cobal t ( I I I) ,

chromium ( I I I) and mangan ese ( I I I) i ons , i n the presence o f bicarbonat e. Such strong , speci fic binding o f co pper ( I I) t o lacto ferrin will not occur in t h e abse nce o f bicarbon­

a t e, ins t e ad only a weak int erac t i on i s o bserve d . L acto­

ferrin has also been shown to weakly bind mangan ese ( !!) , co bal t ( I I) , nickel ( I I), zi nc ( I I) , cadmium ( I I) , l e a d ( I I) and mercury ( I I) , t hough manganese ( !!) will und ergo aeri al o xidation in the prese nce o f t h e pro t ein and bind as

manganese ( I I I). These m e t al i o n pro t e in compl exes h ave b e en examined using the t echniqu es o f fluorescence ,

el ectronic , e . s . r . and Resonance Raman spectrosco py. The cl ose simi l ari ty be t�een the spectra o f the comp l exes Fe2L f , C u2L f , Co 2L f , Mn2L f an d Cr2L f wi th those o f trans f errin and ovo trans ferrin reinforce the postu l a t e that the me t al

binding si t es in all thre e prote ins are simi l ar . The si t es i n all t hre e pro t e i ns are essentially rhombic i n charact er and contain 2 - 3 tyrosyl resi dues and at l east o n e hist idyl r�sidu e. ^A distinc t h e t erogenei ty is evident from t h e e.s . r . spectrum o f Cr2 L f and me t al i on replace�en t stu d i es

i ndica t e that chromium in one si t e is more l abile t h an the o ther . In additi on t o t he s p eci fic si t es lact o fcrr i n

app8ars t o have a number o f non-speci fic si t es o n t h e o u t­

side o f t h e pro tein capabl e of weakly co ordinating m e t al ions such as chromium ( I I I) and cop p er ( I I). Di f ferences evid e n t in the non-speci fic si t es avail able to co p p e r when manganese ( II I) is bound t o l acto ferrin , to t hose avai lable wh en iron ( III) , co balt ( I I I) and chromium ( I I I) are bound , suggest t hat the stronger binding o f manganese ( I I I ) resu l ts

from i t induci ng a di f fere nt conformational change in the pro t e in t o those o ther m e tals and one t hat f avours t he higher st abili ty o f i ts m e t al-pro t e in comp l e x .

A serj_es o f small mo l ecul ar weight compl exes o f i ron ( I I I) wi th bi- , tri- , t e tra- and hexadenta te ligands , cont ain ing phenol a t e groups were prepared and examined by e l ectronic ,

e . s . r . and Mossb au e r spect ro s c o py . Compl exes o f c o p p e r ( I I ) wi th n i t rogen bns e s and c h l o ro- and bromo-subs t i t u t ed

phen o l a t e s we r e prepared and exami n e d by e l e c t ro n i c and e . s . r . spec t ro s c opy . R e su l t s from these s tu di es wou l d

favou r the i n v o l v e m e n t o f thr e e t y ro sy l r e sidu e s a n d t wo c i s hi s t idyl resi du e s i n the m e t al -binding si t e s o f l ac t o ­

ferrin and from studi e s on the c o pp e r c ompl exe s i t s e ems likely that o n e hi s t i dyl and one tyrosyl are axi ally c o ­ o rdinat ed t o t h e m e t al . Evide n c e from a singl e c ry s t a l x-ray s t ru c t u re i s prese n t e d whi c h woul d f avo u r t h e i n t e r­

ac t i o n o f bi c arbonate i o n wi th i ro n ( I I I ) via a s o l ven t ( wat e r ) mo l e c u l e.

(v)

ACKNOWLEDGEMENTS

I am mo s t gra t e ful to :

Dr E . W . A i n s c o u gh and Dr A. M. Bro d i e fo r t h e i r i n ­ valu abl e a s s i s t anc e , advi c e and e n c o u ragem e n t t h ro u gh all stage s o f t his pro j e c t.

Dr W. C . Tennan t , Dr D . G . M c Gavi n and Dr A . R . Gai ns f o rd o f Chemis t ry Divisi o n , D.S . I . R . , Pe t o n e , f o r t h e i r

as s i s t an c e i n running and a n aly s i n g e . s . r . a n d Mos s baue r spec tra and for t h e u s e o f t h e i r Mos s baue r sp e c t ro m e t e r .

Dr K . L . Bro wn o f C hemi s t ry Di vi sio n , D . S . I .R . , Pe t o n e , f o r t h e single c ry s t al x-ray s t ru c t u r al analys i s o f o n e o f my c ompo unds .

Pro fess o r N . F . Cu r t i s o f t h e C h emi s t ry De partm e n t , Vi c t oria U n i ve rsi ty , We l l i ngt o n , f o r the u s e o f h i s Faraday Bal anc e .

Pro fess o r A. D . C ampbell o f t h e C h e mistry D e partm e n t , Ot ago Universi ty , Du n e din , for mic roannly s e s .

Pro fesso r T. M. Lo ehr o f Oregon Graduat e C e n t r e ,

Beave r t o n , Orego n , for run ning and a nalysi ng spec t r a o f some met al - l ac to fe r rin so l u t i o n s.

Dr A . W. Addi son o f the Chemist ry D e partme n t , Drexel Universi t y , Phi l ad e l phia for s uppl y i ng two o f t he l igands u s e d i n Chapt er 2 .

Dr s. V . Rumball , Dr E . N . Bak e r , Dr G . G . Midwi n t e r , Mr A . Trow , Mr S . J. Blo o r and o th e rs o f t h e C hemis t ry/

Bi o c h emist ry /Bio p hysi c s D e partm e n t , I�las s e y Uni ve rs i ty , for t h e i r assi s t ance and a d vi c e .

Mrs L . Reid f o r typing t hi s t hesi s and Mrs J . Tro w f o r pre para t i o n o f s o m e o f t h e d i agram s.

TABLE OF CONTENTS

Page

Abstract . . . . . . . . iii

Acknowl edgements .. . . ^V

Tabl e o f Contents . . . . vi

List o f Figures . . . . vii

List o f T ables . . X

Introduction 1

Chapter 1 Lacto fe rrin

1 . 1 Intro duction 1 0

1 . 2 Experim ental 1 0

1 . 3 Resu l ts and Discussion 1 9

1 . 4 Conclusion 58

Chapter 2 Small Hol ecul e Complexes o f I ron

2 . 1 Intro duction ^{• •} . . 60

2 . 2 Experim ental .. 62

2 . 3 Results and Discussion 68

2 . 4 Conclusion . . . . . . 87

Chapte r 3 Smal l t-1olecu l e Complexes o f Coppe r and Manganese

3 . 1 Introduction . . . . 90

3 . 2 Exp e rimental .. . . 92

3 . 3 Results and Discussion 93

3 . 4 Conclusion ^{• •} 1 1 0

Appendix Publications arising from this Thesis 1 1 4

Re ferences 1 1 5

Figure 1

1.1

1 • 2 ( a)

L IST OF FIGURES

Pro posed st ru c ture o f t h e iron binding sit e o f l ac t o fe rrin, trans ferrin and ovo trans fe rrin.

CM-Sephadex C-50 c h romat ography o f t h e supernat ant prepared from human milk . SDS polyacry l amide ge l e l e c t rophoresis

two bands eluted from a CM-S ephad e x C-50 c o l umn .

( b) SDS po lyacrylamide ge l e l e c t ropho resis 1.3

1.4

1 . 5

1 .6

1 . 7

1.8

1.9

1 . 10

1 . 11

o f l a c t o fe rrin .

Po lyac rylamid e gel e l e c t ro pho resis o f lac t ofe rrin at pH 2.9.

Up t ak e o f iron c ompl exes by citrate­

t r e a t e d apolacto fe rrin and apol ac to­

ferrin .

The in flu ence on the u p take o f 1:1 iron- citrate by apolac t o f e rrin o f o ther metal ions .

Visibl e abso rp tion ope c t ra o f Fe2L f and cu2L f , ·in phosphat e bu f fer p H 7 . 6 , 0 . 01M .

Visibl e abso rption s p e c t r a o f c o2L f and Mn2L f, in 'I'ris bu f fe r pH 7.lt, 0.05M .

Visi bl e abso rption spe c trum o f Cr2L f, in Tris buf fer pH 7.4, 0 . 0 5M.

Transition metal compl exes o f Mn2L f , Co 2L f, Fe2L f, Cu2Lf and Cr2L f .

E. S . R. spe c t r a at - 160°C o f ( a) Fe 2L f in phosphat e bu f fer, pH 7. 6, 0 . 01M,

and Fe 2Lr in phosphate bu f fer titrat e d t o p H 2.0 wit h ( b) citric acid and ( c)

phosphoric acid . /

E . S.R. spectra at -160°C o f a so lution

( vii)

Page

7

12 14

15

21

24

31

32

33

34

38

39

1 . 12

1. 13

1.

14

1.

15

1.

16

2 . 1 2 . 2 2 . 3

2 . 4

2 . 5

containing 1 mole o f ferric perchlor­

ate and 3 moles o f ci tric acid at ( a ) pH 2 . 0 , ( b ) pH 4 . 1 and ( c ) pH 4 . 7.

E . S . R . spec tra at -160°C i n phosphat e bu f fer 0.01M , pH 7 . 6 o f ( a) cu2Lf , ( b ) 2 molar equivalents o f copper(II )

added to Fe2Lf and ( c ) bic arbonate­

free copper-lac to ferrin .

E . S . R . spec tra at -160°C o f ( a ) c opper ( I I ) i n Tri s bu f fer , pH 7.4 , 0 . 05M and 2 molar equivalen t s o f

c opper ( I I ) added t o ( b ) Mn2L f and ( c ) Cr2Lf i n Tris bu f fer .

E . S.R . spec tra at - 1 60°C o f ( a) and ( b) Cr2Lf in Tris bu ffer and ( c )

cr2L f after the addi tion o f one molar equivalen t o f iron ( III ) .

Resonanc e Raman spectra o f ( a) Fe2L f , ( b) Cu2Lf , ( c ) Co2Lf , ( d ) Mn2Lf and (e ) Cr2Lf .

Resonance Raman exci tati o n pro files o f ( a ) Co2Lf , ( b ) Cu2Lf and ( c ) Fe2Lf.

Nomenclature and struc ture o f the ligands c omplexed with iron ( III ) . The molecular con formation of

[Fe (IIIa) 2( MeOH ) 2]No3. MeOH . Visible absorption spec tra o f

( Fe (IIIa) 3 ] 1iH20 and [ Fe ( IIIa) 2 ( MeOH ) 2 ] No3 . 2H20 in methanol , and di f fuse

re flec t ance spec trum o f [Fe (IIIa) ( HeOH ) 4 ] 2+ .

E . S.R . spec tra at -160°C o f ( a) [Fe ( IIIa) .J 1;1-H20 and ( b) [Fe( I I Ia) 2 ( MeOH ) � No3 . 2H20 in Acetone , and ( c )

[Fe ( IV) 3]1tH20 in CH2Cl2 •

E . S . R. spec tra

^at

- 1 60°C o f ( a)

42

43

46

53

56 61 71 76

80

81

2 . 6

2 . 7 2 . 8

3 . 1 3 . 2

3 . 3

3 . 4

3 . 5

3 . 6

[ Fe ( VIIa) J PF 6 in Acetone and ( b) [ Fe ( VIIb) ] PF6 i n HeOH .

E . S . R . spe c tra at -160°C i n MeOH o f ( a) a 1: 1 solu tio n o f Fe ( Cl04) 3 and VIII, ( b ) a 1:1: 1 solution o f

Fe ( Cl04) 3 , VIII and imidazole and ( c ) excess imidazole added to ( b) .

Room temperature Mossbauer spec t ra o f ( a ) Na [ Fe ( Va) ] 4H20 and ( b ) [ Fe ( II ) 3 ] . Room t emperature Mossbauer spe c t ra o f

( a) [ Fe ( IIIa) 3] l iH20 , ( b) [ Fe (IIIa) 2 ( }1eOt02] No3 . 2H20 , ( c ) [Fe ( IIIb) ;J 4H20

and [Fe ( IV3 ) ] 1tH20.

Nomenclature and struc tures o f the ligands c ompl exed wi th c opper(II ) . Visible absorption spec t ra o f [ cu ( tbp ) 2( en )] and [ cu ( tbp ) 2 ( py ) 2 ] in ethanol .

E . S . R . spec tra at -194°C of

^(a)

[ cu ( tbp) 2 ( py ) 2 ] in ethano l and ( b ) [cu ( cyc l am ) (pc p ) 2 ] in dm f�

E . S.R . spe c t ra at - 1 94°C o f ( a )

[ cu ( pc p ) 2 ( coll idine )] i n ac etone and ( b ) [ cu ( pc p ) 2] i n methanol .

Visible abso rption spec trum o f

[Mn (SALENH4 ) ( Ac etato )] (Acetone ) 17H2o in EtOH .

Proposed c o o rdination sphere o f iron ( III ) i n the binding site o f lac to ferrin , trans ferrin and o va­

trans ferrin based on the evidence presented i n this thesis.

/

Cix)

82'

85 86

9 1 99 106

1 07

1 1 1

1 1 3

Table 1

^•

2.

1 . 1

1 . 2 1 . 3

1 . 4

1 . 5 1 . 6

LIST OF TABLES

Concentration of lac tofe rrin in various mam­

malian milks .

Approximate concentration of l ac toferrin i n various secretions .

Times required to hal f satur ate-Apolac to­

ferrin and Apotransferrin with Iron ( III ) and Copper ( II) .

Fluorescence Quenching o f Apolac toferrin by Dival ent and Trivalent Metal Ions .

Binding of l1anganese ( I I ) and Cobal t (II ) by Apolac toferrin after the addi tion o f

Hydrogen Peroxide .

Binding of Manganese ( !! ) and Cobal t ( I I ) to Apolac tofe rrin in the absence of Hydrogen Peroxide.

Binding of two I ron ( I I I ) Equi valen t s by Me tal-Lac toferrin Complexes.

El e c t roni c Spec t ral Dat a for Human Lac to­

ferrin Complexes .

Page 2 2 22

26 28

28

29

30

1 . 7 Electroni c Spectral Data for Cr ( III ) Complexes. 36 1 . 8 Charac terisation

^of

Iron ( III ) High Spin 40

E . S.R . Spe c tra . 1 . 9

1 . 10

L 1 1

1 . 12 1 . 1 3

E . S . R . Spectra o f Complexes of Iron ( III ) wi th Lactoferrin .

E.S . R . Spec tra of Complexes o f Chromium ( II I ) with Lac toferrin and NTA .

E.S . R . Spec tra of Complexes of Copper (II ) wi th Lac toferrin and Copper (!! ) i n Buf fer Solutions .

E.S . R . Spec tra of Copper (II ) added to Fe2L f , cr2L f and Mn2L f .

Bond Lengths o f Manganese (II I ) Complexe s .

44 45 48

48

51

1 . 14 2 . 1

2 . 2

2 . 3

2 . 4

2. 5

3 . 1 3 . 2

3 . 4

3 . 5

Raman Spec tral Data for Native and Metal­

Substi tu t ed Human Lac toferrin .

Analytic al Data of Small Molecular Weight Ferric Ion Complexes .

Condu c ti vities and Magnet i c Susceptibi li t­

ies of Small Molecular Weigh t Ferric Ion Complexes .

El ectronic Spectra of Small Molecular Weight Ferri c Ion Complexes .

Elec tron Spin Resonanc e Spec tra of Small Molecular Weight Ferric Ion Complexes . Mossbauer Spec tral Data o f Small Molecular Weight Ferric Ion � omplexes .

Colours and Analytical Dat a for the Copper Phenolate Complexes .

Conduc tivities and Magnetic Moments for the Copper Phenolate Complexes .

Diffuse RGflec t ance Spec tra of the Copper Phenolate Compl ex e s .

Electronic Solution Spec tra o f the Copper Phenolate Complexes .

Electron Spin Resonanc e Spec tra of the Copper Phenolate Compl exes .

(

xi

⁾

54 66

67

74 79

84

94 9 5

100

101

108