BIOCHEMICAL MEDICINE 4. 408-417 ( 1Q70)

Studies of the AfFinity of Nuclear Material for Uroporphyrin

III. Histones, Nucleic Acid,s, and Bases’

EUGENIA DAVIS, IRENE HOSSENMAIER, G. R. HARTMANN, KEN MIYAGI, A. MOSCOWITZ, Z. J. PETRYKA, AND

C. J. WATSON

Department.s of Medicine and Chemistry, Vnizjersity of Minnesota, Minneapolis, Minnesota 55455, and Vnicersity Medical Research Unit, Northwestern

Ilospital, Minneapolis, Minnesota 55407

Received August 13, 1970

In papers I and II of this series the affinity of nuclei for uroporphyrin was described ( 1,2). In these studies Ehrlich ascites tumor (EAT) cells and phytohemagglutinin (PHA) stimulated lymphocytes were employed. As contrasted with “primary” fluorescence observed in untreated EAT cells, “secondary” fluorescence, after treatment with 0.1 N HCI glycerol pyridine or methanol ammonia, was more frequent and more intense than could be explained on the basis of a simple intensification of fluo-

rescence prior to their use. Thus it seemed likely that complexing had occurred between nuclear elements and the uroporphyrin (1). Since uroporphyrin is the most hydrophilic of the naturally occurring porphy- rins, it was not surprising that it readily cantered these cells and their nuclei.

In respect to the possibility of complexing with nuclear material it was of special interest that when nuclei were prepared from EAT cells of mice which had received uroporphyrin intraperitoneally 3 hours be- fore aspiration, the nuclei alone showed strong red fluorescence in ultra- violet light ( 1) but. more important, their chromosomes also fluoresced quite intensely after the many and various washings in the method of chromosome preparation which was used (3).

The present study, intended to obtain evidence for or against corn- plexing of nuclear materials with uroporphyrin, was divided into several parts, including spectral effects, dialysis, coprecipitation, and Sepha&x gel filtration of solutions containing uroporphyrin with various nuclear components.

‘Supported by Grants P402B from the American Cancer Society and the Mar- garet H. and James E. Kelley Foundation.

408

COMPLEXES OF UROPORPHYRIN AND NUCLEAR COMPONENTS

MATERIALS AND METHODS

409

Materials and Source. In the following all the various nuclear compo- nents which were used are listed, together with their source. Those which were employed in any given type of study are specified under Results and Discussion.

13ysine-rich histone (LRH) / Arginine-ric*h hisbonc CARHi * DNA i

hIirsky lyhine-ricah hist,one (LILRH) ’ Rlitsky arginine-rirh histone (MARH) t

Nucleohistone (NH) (Calbiochem, Los Angeles, Calif.‘l DNA (Sigma, St. Louis, hlo. and Calbiochem’l

RNA-from Baker’s yeast Type III (Sigma) RNA-from Baker’s yeast Type XI (Sigma\

I

Prepared from calf thymus by the method of hIirsky (4)

SlIpplied through the cour- tesy of Prof. A. E. Mirsky, Rockefeller University, New York, N. Y.

Molecular weight was un- known and could range from 12,000 to 140,000 (from correspondence with Sigma)

‘I’hymine (Sigmaj liracil (Sigmaj Cytosine (Sigma) Guanine (Sigma) Adenine (Sigma) Poly-tlysine (Miles Lab., Elkhart, Ind.) Poly-Lglutamic acid (Sigma) Human albumin-salt poor (Courtland Lab., Los Angeles, Calif.)

Uroporphyrin I-isolated as crystalline methyl ester from bovine por- phyria urine (5). This contains about 5% uroporphyrin III. Before use this was saponified on standing overnight in 7.5 N HCl. On adjusting the pH to 4.0 (acetic) the free porphyrin was precipitated, washed with dilute acetic, collected on a fine sintered glass funnel and dissolved in triple distilled water, pH 6.4. The amount of uroporphyrin in various fractions mentioned in the following was determined fluorimetrically in 1.5N HCl (6).

Spectral Effects. All of the absorption spectra were recorded in a Beckman DK spectrophotometer, in aqueous solution pH 6.4, unless otherwise indicated. Quartz cells of l-cm path length were used. Care must be taken to wash the cells out completely each time as the nuclear material and uroporphyrin tend to adhere strongly. Distilled water, with a pH as low as 5.6 (atmospheric CO,), was adjusted to pH 6.4 with 0.1 N I&OH or 0.1 N HCl. The present studies were carried out in

410 DAVIS ET Al..

water at pH 6.4 which was found to be optimal in respect to definition of spectral change for uroporphyrin in the presence of another compound, especially in the SOO-6OO-n111 region. The complex was more labile when in a more acidic or more basic solution.

Dialysis. Uroporphyrin was dissolved in phosphate buffer, pH 7.4, or water, pH 5.6. It was then subjected to dialysis with appropriate nuclear components (see Results) in water. After 12 hours the water solution was examined under UV light’ for red fluorescence. Dialysis tubes were again placed in water and the process was repeated after 24 and 48 hours. Great care was taken to avoid leaks.

Coprecipitations. These were’ carried out in all instances with a pri- mary aqueous solution of uroporphyrin and a given nuclear component (see Results). The solution was allowed to stand for 2 hours in the dark to exclude spontaneous precipitation after which it was diluted 1:lO with acetone and thoroughly mixed. Uroporphyrin alone is soluble in acetone in the concentrations used. Any precipitate was centrifuged and the uroporphyrin in the supernate determined. The precipitate was extracted three times with 10 ml portions of 1.5 s WC1 and the amount of uropor- phyrin was determined. Undissolved precipitate was dissolved in 0.5 ml of 10% NaOH, mixed with sufficient 3.0 N HCI to make a final concen- tration of 1.5 N and the uroporphyrin content determined.

Sephudex Gel Filtration. Sephadex G 200 in 0.0007 M phosphate buf- fer ( KzHPOa:KHzPO,) eluted with 0.0007 M phosphate buffer, pH 6.8 was applied on a column 44 mm in diameter and 50 cm long. The uropor- phyrin sample was dissolved in the buffer and mixed with the nuclear component being tested, kept at 4” for 24 hours, and then applied on the column. A control was run with uroporphyrin alone. Samples of eluant, about 15 ml, were collected from the column and absorption spectra were recorded with special reference to any changes at 250-280 and 390420 nm. The various nuclear components examined are given in the following under Results. Human serum albumin was also tested in this manner.

RESULTS AND DISCUSSION

Spectral Studies. In Fig. 1 the uroporphyrin spectrum is highly sensi- tive to pH changes. The extinction coefficients as well as band shapes and positions vary. Falk (7) h as g iven some information as to variations related to mono- and dication and neutral forms, a Soret and three visible bands, the Soret being at a shorter wavelength than that of the corresponding neutral porphyrin. The dication and dianion forms

’ M~~gndlux Black l.ight. Magnaflus Corp., Chicago. III.

COMPLEXES OF UNROPORPHYRIh’ AND ‘ZCLEAR COMPONENTS 411

FIG 1. Spectra of Uro- at different pl-I values. Left and middle panels show variation in Soret band shape and intensity; concn. 0.277 mg%. Panels at right show variations in spectra, 450-650 nm, concn. 0.9 mgP%.

reveal one distinct band with smaller bands and shoulders on either side to a total of four bands. The Soret band of the dication and dianion is displaced to a longer wavelength in relation to the corresponding neutral porphyrin.

The results of the spectral studies of mixtures of nuclear components and uroporphyrin are given in Table 1. Reproduction of the more signii?- cant absorption spectra is shown in Fig. 2. It is evident that a rather marked perturbation occurred with LRH, ARH, human albumin, and poly-L-lysine. With these components a definite shift of the Soret band is noted, as well as a reversal of the absorption intensity, also a signifi- cant shift of the 560 nm maximum to 572 nm. In contrast, poly-rcglu- tamic acid had no effect on the porphyrin spectrum. The perturbation by RNA was quite outspoken (Fig. 2). It was noted, however, that different molar proportions of RNA were required, depending on the type of RNA used (see Table 1). There was a slight or questionable perturbation by DNA, an example being shown in Fig. 2 and further data in Table 1. DNA obtained from Calbiochem and Sigma gave similar results. The small perturbation as noted in Fig. 2 required a mol/mol ratio which produced a gel-like solution; hence the physical conditions differed significantly, as with the uroporphyrin alone the measurement was made

TAB1

3 1

Rru.

73.u

. ~“

E~~I

~ILJ

LITJ

O~~

O

F UR

OPO

KPHY

R~N

UPOX

M

IST~

IIJC

w

ITI%

Y.

~l:to

ub

Kr:c

Lb:.i

i~

CO

MPV

SEST

~ --.

. ---

..-

----

-- -..

-

Abso

rptio

n ba

nds

(rim

]

Urop

orph

yrin

+ nu

clear

co

mpo

nent

ITro

porp

hyrin

al

one

MLR

H M

ARH

Hum

an

albu

min

Po

ly-L-

lysine

Po

ly-tg

luta

mic

acid

l)X\;A

(C

albioc

hem

)

1 )NA

(S

igm

a’

RNA-

Type

XI

_.--

Mola

r ra

tio

com

p/ur

o So

rer

407

1:l

395

1:l

395

1:l

395

1:l

395

ca5:

l 40

7

1:l

400

1:l

400

407

I II

.i;;o

54

0

505

540

a6

540

506

540

506

540

506

540

505

540

505

540

505

540

540

III

Orde

r of

56

0 in

tens

ity

560

III,II

,I

572

I,II,I

II 57

2 I,I

I,III

573

I,II,I

II 57

2 I,I

I,III

560

III,II

,I

360

II,III

,I

560

II,lII

,T

36X

II.11

1

- ..-

RNA-

Type

III

NH

MLR

H +

DNA

Aden

ine

Cyto

sine

1:l

1:l:l

200:

1

600:

1

399

505

540

567

407

50.5

34

0 56

0 40

7 50

5 54

0 56

0 40

6 0 -0

- n

540

567

406

505

540

563

II,III

,I

III,II

,I III

,II,I

LII,I

I,I

III,II

,I

hlol

. wt

W

~MJW

-I~,

het~

ce

myla

r ra

tios

coul

d no

t be

ca

lcnla

ted

(see

M

ater

ials)

Mola

r ra

t,io

is M

LRII:

L)NA

: Ur

o.

Pertu

rbat

ion

was

max

imal

at

mola

r ra

tio

show

n Pe

rturb

ation

wa

s m

axim

al :tt

m

da~

Thym

ine

600:

I*

40i

ratio

sh

own

505

540

560

III,II

,I 4 2 2

---__

__

%

* Ti

.ese

ra

tios

were

th

e hig

he>t

wh

ich

co11

1d

be

achie

ved

due

to

relat

ive

inso

hlbi

litp

of

the

pyrim

idine

ba

ses.

u z 9

414

FIG. 2. Spectra of Uro- alone and with DNA, RNA (Type XI), and LRH, at

pH 6.4 - Uro-; - - - Uro- +DNA; - - - - Uro- +RNA (Type XI); ---- Uro- +LRH. (See Methods and Table 1 for further details.)

in a simple liquid whereas with the DNA in the amount required, a solid solution was approached. Thus it may be assumed that the orien- tation of the molecules was altered and relatively fixed.

It is highly significant that NH did not produce any spectral pertur- bation of uroporphyrin despite its relatively high content of lysine- and arginine-rich histones, both of which alone produce definite perturbation. It was of interest that when MLRH was mixed with commercial DNA, the perturbation observed with MLRH alone disappeared. This indicates a preferential occupation of the histone’s activity binding sites by DNA as contrasted with uroporphyrin. This also explains why NH produces no spectral perturbation when mixed with DNA. The results with al- bumin and poly-L-lysine were entirely similar with those obtained with the lysine- and arginine-rich histones.

Of the pyrimidine bases only adenine and cytosine showed perturba- tion of the uroporphyrin spectrum (Table 1). This was maximum with cytosine at a 6OO:l molar ratio, and with adenine at a 2OO:L ratio. Guanine is insoluble in water at neutral pH but soluble in dilute alkali. At a molar ratio of guanine and uroporphyrin up to 6OO:l in dilute alkali no spectral perturbation was observed. Uracil and thymine were studied from a 4O:l up to 6OO:l base:uroporphyrin ratio and they showed no

COMPLEXES OF UROPORPXYRIN AND KUCLEAR COMPONENTS 415

spectral perturbation. The lack of any spectral shift of the Soret band and the adjacent band at 540 nm is in accord with usual experience that bands furthest in the red are the most affected. It should be noted that the 612-nm band is too weak for observation under our experimental conditions.

Several attempts were also made to see if the perturbing influence of DNA, RNA, or MLRH would manifest itself by inducing optical activity in the transitions of the uroporphyrin molecule. Such effects have been observed, for example, by the influence of polypeptides on acridine orange (8). However, under conditions similar to those for which per- turbations were observed in the absorption spectrum of uroporphyrin, no such optical activity could be seen. Since the requisite symmetry conditions were satisfied for the appearance of induced optical activity in the uroporphyrin bands, we conclude that manifestation of, for ex- ample, a uroporphyrin-MLRH complex through optical activity is below the sensitivity of our instrument (Cary 60 spectropolarimeter with CD attachment) under the conditions used.

Diulysis. In the dialysis experiments all of the histone samples, DNA, RNA of the two types, and NH prevented dialysis of the uroporphyrin, whereas uroporphyrin alone in water readily dialyzes out. A small pro- portion, however, fails to dialyze, probably because of aggregation of molecules. The possibility cannot be excluded that aggregation is en- hanced in the presence of the larger molecules of the nuclear component tested, and that this explains the lack of correlation of these results with those of the spectral perturbation or coprecipitation studies. It is not unlikely that with such large molecules trapping of the uroporphyrin without actual complexing might account for failure of dialysis.

Coprecipitatim. The results of the coprecipitation studies accord re- markably well with those related to spectral perturbation (Table 2). The experiments with RNA (Types III and XI) were unsatisfactory due to solubility in the 1O:l acetone mixture. On addition of more RNA it still failed to precipitate but formed a gel-like collection at the bottom of the tube which fluoresced rather strongly in contrast with the super- nate although the latter still contained uroporphvrin. An accurate quantitative determination proved impossible.

In general, however, the results of the coprecipitation experiments reinforce those of the spectral perturbation studies. Thus it is seen in Table 2 that large amounts of uroporphyrin precipitated with LRH, ARH, and albumin, the compounds which produced the most marked spectral perturbation, while with DNA and NH with questionable or no spectral change, the coprecipitation was relatively small and may not relate to actual complexing.

416 DAVIS ET AL.

TABLE: 2 ~~OPRECIPITATIOi%S OF hOI’OHPHYRIS WITH ~UCLISAK (‘OMPONKhT5

ANLI OTIIER COMPOUNDS .___-

’ ;, Total recovered uroporphyriti prehc~li ill :

(1 1 I’recipilarr

Human albumin DNA (Sigma) NH MLRH MARH Poly-L-glutamic acid Poly-Llysine RNA-Type III RNA-Type XI

100

2::

2s. :J,

80 5

ti9. ti 0

Did not precipitate or~t 110 not yield well defined precipitates

hllt gels settled which fluoresced rather strongl>

-

Poly-L-glutamic acid which produces no spectral perturbation showed no fluorescence in the precipitate in the coprecipitation experiment. We could not compare this with poly-L-lysine which produces spectral changes, since it did not precipitate out in the acetone-water mixture.

The coprecipitation method was unsatisfactory with the pyrimidine bases, due to their solubility both in acetone-water and other solvent systems which were tried. These included ethanol-water, 60% ammonium sulfate in water, cyclohexane-water, and cyclohexanone-water two phase systems.

Sephadex Gel Filtration. No evidence of complexing was observed when solutions of uroporphyrin with NH, DNA (Calbiochem and Sigma), both types of RNA, LRH, or poly-L-lysine were subjected to Sephadex gel filtration. Human albumin, however, shows complexing with uroporphyrin on Sephadex gel filtration. This difference is believed due to a stronger complex of uroporphyrin with albumin than with the former compounds.

SUMMARY AND CONCLUSIONS

A series of studies have been carried out to determine the occurrence and relative strength of complexing of uroporphyrin with various nuclear components, including NH, DNA, RNA, lysine- and arginine-rich his- tones, poly+lysine, poly-L-glutamic acid, and five pyrimidine bases. Human serum albumin was also studied in this respect. Significant spectral perturbation of uroporphyrin was noted with both LRH and ARH, poly-L-lysine and RNA. With DNA the perturbation was slight

COMPLEXES OF UROPORPHYRIN AND NUCLEAR COMPONENTS 417

or questionable, but absent with NH. Minor perturbation was noted with adenine and cytosinc, none with thymine, uracil, or guanine. Copre- cipitation studies yielded results in agreement with those of spectral perturbation, large proportions of the porphyrin precipitating with the two histones and albumin but not with DNA, NH, or poly-L-glutamic acid. Due to solubility in acetone-water and other solvent systems, coprecipitation could not be studied satisfactorily with the pyrimidine bases. Lack of evidence of complexing on Sephadex gel filtration, except with serum albumin, is believed due to differential competition with the weaker complexes of uroporphyrin with tho histones, RNA, and poly-L-lysine.

REFERENCES

1. MIYAGI, K., HARTMANN, G. R., RUNGE, W., AND WATSON, C. J., Biochem. Med. 4, 391 ( 1970).

2. HARTMANN, G. R.,, AND WATSON, C. J., B&hem. Med. 4, 403 (1970). 3. CANTOR, K. P., AND HEARST, J. E., Proc. Nat. Acad. Sci. U. S. A. 55, 642 ( 1966). -1. MIRSKY, A. E., BIJRDXCK, C. J., DAVIDSON, E. H., AND LITTAU, V. C., Proc. Nat.

Acad. Sci. U. S. A. 61, 592 (1968). 5. CARDINAL, R., BOSSENMAIER, I., PETRYKA, Z. J., JOHNSON, I,., AND WATSON, C.

J., J. chromutogr. 38, 100 (1968). 6. SCHWARTZ, S., BERG, M. H., BOSSENMAIER, I., AND DINSMORE, H., in “Methods

of Biochemical Analysis” (David Click, ed. ), Vol. 8, p. 221. Interscience, New York, 1960.

7. FALK, J. E., “Porphyrins and Metalloporphyrins,” Vol. 2, BBA Library. Elsevier, New York, 1964.

8. BLOUT, E. R., BioPolymers Symposia No. 1, 1964, p. 397.