Document:

<PAGE>   1
                                                                    EXHIBIT 4.16

                       ASSIGNMENT AND ASSUMPTION AGREEMENT

                                       to

                               GUARANTEE AGREEMENT

                                     between

                         AMERICAN MUTUAL HOLDING COMPANY

                                       and

                           AMERUS LIFE HOLDINGS, INC.

                            Dated September 20, 2000

<PAGE>   2

                       ASSIGNMENT AND ASSUMPTION AGREEMENT

     This ASSIGNMENT AND ASSUMPTION AGREEMENT ("Agreement"), dated as of
September 20, 2000, is entered into by and between AMERICAN MUTUAL HOLDING
COMPANY, an Iowa mutual insurance holding company ("AMHC") and AMERUS LIFE
HOLDINGS, INC., an Iowa insurance holding company ("AmerUs").

                                   WITNESSETH:

     WHEREAS, AmerUs and Wilmington Trust Company, a banking corporation duly
organized and existing under the laws of Delaware, as trustee (the "Property
Trustee" or "Guarantee Trustee"), entered into a Trust Agreement, dated as of
October 4, 1996 (the "Original Trust Agreement"), to establish a business trust
pursuant to the Delaware Business Trust Act;

     WHEREAS, AmerUs, the Property Trustee, the Administrative Trustees named
therein, and several Holders as defined therein entered into an Amended and
Restated Trust Agreement (the "Trust Agreement"), dated as of February 3, 1997,
to provide for, among other provisions, the issuance and sale of the Capital
Securities by the Trust;

     WHEREAS, AmerUs and the Guarantee Trustee, for the benefit of the Holders
from time to time of the Capital Securities, executed and delivered a Guarantee
Agreement, dated as of February 3, 1997 (the "Guarantee Agreement"), whereby
AmerUs irrevocably and unconditionally agreed, to the extent set forth in the
Guarantee Agreement, to pay to the Holders the Guarantee Payments and to make
certain other payments on the terms and conditions set forth in the Guarantee
Agreement;

     WHEREAS, AMHC has executed a Plan of Conversion, dated as of December 17,
1999, pursuant to which AMHC will convert from a mutual insurance holding
company into a stock holding company;

     WHEREAS, AMHC and AmerUs have entered into an Agreement and Plan of Merger,
dated December 17, 1999, pursuant to which AmerUs will merge with and into AMHC,
with AMHC as the surviving company (the "Merger");

     WHEREAS, AMHC desires to assume AmerUs' obligations under the Guarantee
Agreement;

     WHEREAS, this Agreement is being executed pursuant to Section 8.01 of the
Guarantee Agreement;

     WHEREAS, as required by Section 8.01 of the Guarantee Agreement, the Merger
is permitted under Article Eight of the Indenture;

<PAGE>   3

     NOW, THEREFORE, the parties agree as follows:

SECTION 1.   Assignment.  Upon the execution of this Agreement by the parties
             hereto, AmerUs does hereby assign and transfer all of its
             obligations under the Guarantee Agreement to AMHC, as its
             successor.

SECTION 2.   Assumption. Upon the execution of this Agreement by the
             parties hereto, AMHC does hereby absolutely and irrevocably
             accept the foregoing assignment and hereby assumes to be
             solely responsible for and to perform, as successor, AmerUs'
             obligations under the Guarantee Agreement.

SECTION 3.   Definitions. For all purposes of this Agreement, except as
             otherwise herein expressly provided, the definitions, terms
             and expressions used herein shall have the same meanings as
             corresponding definitions, terms and expressions used in the
             Guarantee Agreement.

SECTION 4.   Effectiveness.  This Agreement shall become effective as of the
             Effective Time (as defined in the Agreement and Plan of Merger
             referred to above) of the Merger.

SECTION 5.   Binding Effect; Assigns.  This Agreement shall be binding upon,
             and shall enure to the benefit of, the parties thereto and their
             respective successors and assigns.

SECTION 6.   Counterparts.  This Agreement may be executed in two or more
             counterparts, each of which will be deemed to be an original, but
             all of which together will constitute one and the same agreement.

SECTION 7.   Governing Law.  This Agreement will be governed by and
             interpreted in accordance with the internal laws of the State of
             New York, without giving effect to principles of conflicts of
             laws.

     IN WITNESS WHEREOF, the parties hereto have executed and delivered this
Agreement as of the date set forth above.

                                            AMERICAN MUTUAL HOLDING COMPANY

                                            By: /s/ Roger K. Brooks
                                                -------------------------------
                                                Name:  Roger K. Brooks
                                                Title: Chairman, President and
                                                       Chief Executive Officer

<PAGE>   4

                                            AMERUS LIFE HOLDINGS, INC.

                                            By: /s/ Roger K. Brooks
                                                -------------------------------
                                                Name:  Roger K. Brooks
                                                Title: Chairman, President and
                                                       Chief Executive Officer<PAGE>   1
                                                                   EXHIBIT 4.17

                                FIRST SUPPLEMENT

                                       to

                                    INDENTURE

                                      among

                        AMERICAN MUTUAL HOLDING COMPANY,

                           AMERUS LIFE HOLDINGS, INC.

                                       and

                      FIRST UNION NATIONAL BANK, as Trustee

                          Date as of September 20, 2000

<PAGE>   2

                          FIRST SUPPLEMENTAL INDENTURE

     This FIRST SUPPLEMENTAL INDENTURE (this "First Supplemental Indenture") is
made as of the 20th day of September, 2000, among AMERICAN MUTUAL HOLDING
COMPANY, an Iowa mutual insurance holding company ("AMHC"), AMERUS LIFE
HOLDINGS, INC., an Iowa insurance holding company (the "Company"), and FIRST
UNION NATIONAL BANK, as Trustee (the "Trustee").

                                   WITNESSETH:

     WHEREAS, the Company and the Trustee executed and delivered an Indenture,
dated as of July 27, 1998 (the "Indenture"), providing for the issuance by the
Company of its unsecured and subordinated debentures, notes or other evidences
of subordinated indebtedness;

     WHEREAS, AMHC has executed a Plan of Conversion, dated as of December 17,
1999, pursuant to which AMHC will convert from a mutual insurance holding
company into a stock holding company;

     WHEREAS, the Company and AMHC have executed and delivered an Agreement and
Plan of Merger, dated December 17, 1999, pursuant to which the Company will
merge with and into AMHC, with AMHC as the surviving company (the "Merger") and
AMHC will thereafter change its name to AmerUs Group Co.;

     WHEREAS, AMHC desires to assume the obligations of the Company under the
Indenture;

     WHEREAS, this First Supplemental Indenture is being executed pursuant to
the requirements of Article Seven of the Indenture, as authorized by Article
Eight of the Indenture and without the consent of the Holders;

     WHEREAS, the execution and delivery by the Company of this Supplemental
Indenture have been duly authorized by Board Resolution and all other action
required to make this First Supplemental Indenture a valid and binding
instrument has been duly taken and performed; and

     WHEREAS, concurrently with the execution and delivery of this First
Supplemental Indenture, the Company is delivering to the Trustee an Officers'
Certificate and an Opinion of Counsel, each stating that the Merger and this
First Supplemental Indenture comply with this Indenture and that all conditions
precedent to the consummation of the Merger under this Indenture have been met.

     NOW, THEREFORE, the parties agree as follows:

<PAGE>   3

                                   ARTICLE ONE
                                   ASSUMPTION

     SECTION 1.01. AMHC hereby assumes the due and punctual payment of the
principal, premium, if any, interest, if any, and any Additional Amounts, with
respect to all of the Securities and the performance or observance of every
covenant under this Indenture and the Securities on the part of the Company to
be performed under the Securities, the coupons and this Indenture.

                                   ARTICLE TWO
                                  MISCELLANEOUS

     SECTION 2.01. Definitions. For all purposes of this First Supplemental
Indenture, except as otherwise herein expressly provided, the definitions, terms
and expressions used herein shall have the same meanings as corresponding
definitions, terms and expressions used in the Indenture.

     SECTION 2.02. Continuance of Indenture. This First Supplemental Indenture
supplements the Indenture and shall be a part of and subject to all the terms
thereof. The Indenture, as supplemented and amended by this First Supplemental
Indenture, is in all respects ratified and confirmed, and the Indenture and this
First Supplemental Indenture shall be read, taken and construed as one and the
same instrument.

     SECTION 2.03. Concerning the Trustee. The Trustee accepts the amendment of
the Indenture effected by this First Supplemental Indenture and agrees to
execute the trust created by the Indenture, as hereby amended, but only upon the
terms and conditions set forth in the Indenture, as hereby amended, including
the terms and provisions defining and limiting the liabilities and
responsibilities of the Trustee, which terms and provisions shall in like manner
define and limit its liabilities in the performance of the trust created by the
Indenture, as hereby amended.

     SECTION 2.04. Governing Law. This First Supplemental Indenture shall be
governed by and construed in accordance with the laws of the State of New York
without regard to the principles of conflicts of laws.

     SECTION 2.05. Counterparts. This First Supplemental Indenture may be
executed in any number of counterparts, each of which when so executed shall be
deemed to be an original, and all of such counterparts shall together constitute
one and the same instrument.

<PAGE>   4

                                  ARTICLE THREE
                                     NOTICE

     Section 1.05 of the Indenture shall be amended to delete the Trustee's
notice address and insert the following notice in lieu thereof:

                  401 South Tryon Street
                  12th Floor
                  Charlotte, NC  28288-1179

     IN WITNESS WHEREOF, the parties hereto have caused this Indenture to be
duly executed, and their respective corporate seals to be hereunto affixed and
attested, all as of the day and year first written above.

                                            AMERICAN MUTUAL HOLDING COMPANY

                                            By: /s/ Roger K. Brooks
                                                -------------------------------
                                                Name:  Roger K. Brooks
                                                Title: Chairman, President and
                                                       Chief Executive Officer

                                            AMERUS LIFE HOLDINGS, INC.

                                            By: /s/ Roger K. Brooks
                                                -------------------------------
                                                Name:  Roger K. Brooks
                                                Title: Chairman, President and
                                                       Chief Executive Officer

                                            FIRST UNION NATIONAL BANK

                                            By: /s/ Shawn K. Bednasek
                                                -------------------------------
                                                Name:  Shawn K. Bednasek
                                                Title: Vice President

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00017-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00017-of-00352.parquet"}]]